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1.  Halococcus qingdaonensis sp. nov., a halophilic archaeon isolated from a crude sea-salt sample 
A Gram-negative, extremely halophilic, coccoid archaeal strain, CM5T, was isolated from a crude sea-salt sample collected near Qingdao, China. The organism grew optimally at 35–40 °C and pH 6.0 in the presence of 20 % (w/v) NaCl. Its colonies were red in colour and it could use glucose as a sole carbon source for growth. The 16S rRNA gene sequence of CM5T was most closely related to those of Halococcus species. Its pattern of antibiotic susceptibility was similar to those of other described Halococcus species. Biochemical tests revealed no sign of H2S production or gelatin liquefaction. The main polar lipids of strain CM5T were phosphatidylglycerol, phosphatidylglycerol methylphosphate and sulfated diglycosyl diether. No phosphatidylglycerol sulfate was present. The DNA G+C content of strain CM5T was 61.2 mol% and it gave DNA–DNA reassociation values of 33.7, 57.1 and 29.6 %, respectively, with Halococcus salifodinae DSM 8989T, Halococcus dombrowskii DSM 14522T and Halococcus morrhuae ATCC 17082T. Based on its morphological and chemotaxonomic properties and phylogenetic analysis of 16S rRNA gene sequence data, we propose that CM5T should be classified within a novel species, Halococcus qingdaonensis sp. nov., with strain CM5T (=CGMCC 1.4243T=JCM 13587T) as the type strain.
doi:10.1099/ijs.0.64673-0
PMCID: PMC3182530  PMID: 17329792
2.  A First Record of Obligate Halophilic Aspergilli from the Dead Sea 
Indian Journal of Microbiology  2011;52(1):22-27.
The isolation of obligate halophilic aspergilli from the Dead Sea and the range of salt tolerance of halophilic fungi isolated, are reported here for the first time. The mycobiota of the Dead Sea isolated in this study, was dominated by Aspergillus and Penicillium species; Cladosporium were found in lesser numbers. All three genera were obtained from the water sample; however, Aspergillus was the only genus obtained from the sediment. There was significant difference in growth of each isolate at different salt concentrations and intraspecies analysis revealed dissimilarity in response of strains to different salt concentrations in the growth medium The isolates were euryhaline, with halotolerance up to 20–25% solar salt, Aspergillus and Penicillium species showing a higher level of halotolerance, as compared to that of Cladosporium. Halophilic fungi were found in greater numbers in the sediment sample as compared to that in the water sample. Penicillium and Cladosporium species were exclusively facultative halophiles, while some species of Aspergillus were facultative halophiles. All the obligate halophiles isolated, belonged to the genus Aspergillus and were identified as A. penicillioides and A unguis, the latter being a first record of the species from the Dead Sea.
doi:10.1007/s12088-011-0225-z
PMCID: PMC3298590  PMID: 23449273
Dead Sea; Obligate halophile; Aspergillus; Penicillium; Cladosporium
3.  Identification of polyhydroxyalkanoates in Halococcus and other haloarchaeal species 
Polyhydroxyalkanoates (PHAs) are accumulated in many prokaryotes. Several members of the Halobacteriaceae produce poly-3-hydroxybutyrate (PHB), but it is not known if this is a general property of the family. We evaluated identification methods for PHAs with 20 haloarchaeal species, three of them isolates from Permian salt. Staining with Sudan Black B, Nile Blue A, or Nile Red was applied to screen for the presence of PHAs. Transmission electron microscopy and 1H-nuclear magnetic resonance spectroscopy were used for visualization of PHB granules and chemical confirmation of PHAs in cell extracts, respectively. We report for the first time the production of PHAs by Halococcus sp. (Halococcus morrhuae DSM 1307T, Halococcus saccharolyticus DSM 5350T, Halococcus salifodinae DSM 8989T, Halococcus dombrowskii DSM 14522T, Halococcus hamelinensis JCM 12892T, Halococcus qingdaonensis JCM 13587T), Halorubrum sp. (Hrr. coriense DSM 10284T, Halorubrum chaoviator DSM 19316T, Hrr. chaoviator strains NaxosII and AUS-1), haloalkaliphiles (Natronobacterium gregoryi NCMB 2189T, Natronococcus occultus DSM 3396T) and Halobacterium noricense DSM 9758T. No PHB was detected in Halobacterium salinarum NRC-1 ATCC 700922, Hbt. salinarum R1 and Haloferax volcanii DSM 3757T. Most species synthesized PHAs when growing in synthetic as well as in complex medium. The polyesters were generally composed of PHB and poly-ß-hydroxybutyrate-co-3-hydroxyvalerate (PHBV). Available genomic data suggest the absence of PHA synthesis in some haloarchaea and in all other Euryarchaeota and Crenarchaeota. Homologies between haloarchaeal and bacterial PHA synthesizing enzymes had indicated to some authors probable horizontal gene transfer, which, considering the data obtained in this study, may have occurred already before Permian times.
Electronic supplementary material
The online version of this article (doi:10.1007/s00253-010-2611-6) contains supplementary material, which is available to authorized users.
doi:10.1007/s00253-010-2611-6
PMCID: PMC2895300  PMID: 20437233
Polyhydroxybutyrate; Haloarchaea; Halococcus; Halobacterium; Haloalkaliphile
4.  Growth Potential of Halophilic Bacteria Isolated from Solar Salt Environments: Carbon Sources and Salt Requirements 
Eighteen strains of extremely halophilic bacteria and three strains of moderately halophilic bacteria were isolated from four different solar salt environments. Growth tests on carbohydrates, low-molecular-weight carboxylic acids, and complex medium demonstrated that the moderate halophiles and strains of the extreme halophiles Haloarcula and Halococcus grew on most of the substrates tested. Among the Halobacterium isolates were several metabolic groups: strains that grew on a broad range of substrates and strains that were essentially confined to either amino acid (peptone) or carbohydrate oxidation. One strain (WS-4) only grew well on pyruvate and acetate. Most strains of extreme halophiles grew by anaerobic fermentation and possibly by nitrate reduction. Tests of growth potential in natural saltern brines demonstrated that none of the halobacteria grew well in brines which harbor the densest populations of these bacteria in solar salterns. All grew best in brines which were unsaturated with NaCl. The high concentrations of Na+ and Mg2+ found in saltern crystallizer brines limited bacterial growth, but the concentrations of K+ found in these brines had little effect. MgSO4 was relatively more inhibitory to the extreme halophiles than was MgCl2, but the reverse was true for the moderate halophiles.
PMCID: PMC241517  PMID: 16346609
5.  Low-pass sequencing for microbial comparative genomics 
BMC Genomics  2004;5:3.
Background
We studied four extremely halophilic archaea by low-pass shotgun sequencing: (1) the metabolically versatile Haloarcula marismortui; (2) the non-pigmented Natrialba asiatica; (3) the psychrophile Halorubrum lacusprofundi and (4) the Dead Sea isolate Halobaculum gomorrense. Approximately one thousand single pass genomic sequences per genome were obtained. The data were analyzed by comparative genomic analyses using the completed Halobacterium sp. NRC-1 genome as a reference. Low-pass shotgun sequencing is a simple, inexpensive, and rapid approach that can readily be performed on any cultured microbe.
Results
As expected, the four archaeal halophiles analyzed exhibit both bacterial and eukaryotic characteristics as well as uniquely archaeal traits. All five halophiles exhibit greater than sixty percent GC content and low isoelectric points (pI) for their predicted proteins. Multiple insertion sequence (IS) elements, often involved in genome rearrangements, were identified in H. lacusprofundi and H. marismortui. The core biological functions that govern cellular and genetic mechanisms of H. sp. NRC-1 appear to be conserved in these four other halophiles. Multiple TATA box binding protein (TBP) and transcription factor IIB (TFB) homologs were identified from most of the four shotgunned halophiles. The reconstructed molecular tree of all five halophiles shows a large divergence between these species, but with the closest relationship being between H. sp. NRC-1 and H. lacusprofundi.
Conclusion
Despite the diverse habitats of these species, all five halophiles share (1) high GC content and (2) low protein isoelectric points, which are characteristics associated with environmental exposure to UV radiation and hypersalinity, respectively. Identification of multiple IS elements in the genome of H. lacusprofundi and H. marismortui suggest that genome structure and dynamic genome reorganization might be similar to that previously observed in the IS-element rich genome of H. sp. NRC-1. Identification of multiple TBP and TFB homologs in these four halophiles are consistent with the hypothesis that different types of complex transcriptional regulation may occur through multiple TBP-TFB combinations in response to rapidly changing environmental conditions. Low-pass shotgun sequence analyses of genomes permit extensive and diverse analyses, and should be generally useful for comparative microbial genomics.
doi:10.1186/1471-2164-5-3
PMCID: PMC331400  PMID: 14718067
6.  A traditional Japanese-style salt field is a niche for haloarchaeal strains that can survive in 0.5% salt solution 
Saline Systems  2007;3:2.
Background
Most of the haloarchaeal strains have been isolated from hypersaline environments such as solar evaporation ponds, salt lakes, or salt deposits, and they, with some exceptions, lyse or lose viability in very low-salt concentrations. There are no salty environments suitable for the growth of haloarchaea in Japan. Although Natrialba asiatica and Haloarcula japonica were isolated many years ago, the question, "Are haloarchaea really thriving in natural environments of Japan?" has remained unanswered.
Results
Ten strains were isolated from a traditional Japanese-style salt field at Nie, Noto Peninsula, Japan by plating out the soil samples directly on agar plates containing 30% (w/v) salts and 0.5% yeast extract. They were most closely related to strains of three genera, Haladaptatus, Halococcus, and Halogeometricum. Survival rates in 3% and 0.5% SW (Salt Water, solutions containing salts in approximately the same proportions as found in seawater) solutions at 37°C differed considerably depending on the strains. Two strains belonging to Halogeometricum as well as the type strain Hgm. borinquense died and lysed immediately after suspension. Five strains that belonged to Halococcus and a strain that may be a member of Halogeometricum survived for 1–2 days in 0.5% SW solution. Two strains most closely related to Haladaptatus possessed extraordinary strong tolerance to low salt conditions. About 20 to 34% of the cells remained viable in 0.5% SW after 9 days incubation.
Conclusion
In this study we have demonstrated that haloarchaea are really thriving in the soil of Japanese-style salt field. The haloarchaeal cells, particularly the fragile strains are suggested to survive in the micropores of smaller size silt fraction, one of the components of soil. The inside of the silt particles is filled with concentrated salt solution and kept intact even upon suspension in rainwater. Possible origins of the haloarchaea isolated in this study are discussed.
doi:10.1186/1746-1448-3-2
PMCID: PMC1828056  PMID: 17346353
7.  Lysis of Halobacteria in Bacto-Peptone by Bile Acids 
All tested strains of halophilic archaebacteria of the genera Halobacterium, Haloarcula, Haloferax, and Natronobacterium lysed in 1% Bacto-Peptone (Difco) containing 25% NaCl, whereas no lysis was observed with other strains belonging to archaebacteria of the genera Halococcus, Natronococcus, and Sulfolobus, methanogenic bacteria, and moderately halophilic eubacteria. Substances in Bacto-Peptone which caused lysis of halobacteria were purified and identified as taurocholic acid and glycocholic acid. High-performance liquid chromatography analyses of peptones revealed that Bacto-Peptone contained nine different bile acids, with a total content of 9.53 mg/g, whereas much lower amounts were found in Peptone Bacteriological Technical (Difco) and Oxoid Peptone. Different kinds of peptones can be used to distinguish halophilic eubacteria and archaebacteria in mixed cultures from hypersaline environments.
PMCID: PMC202585  PMID: 16347619
8.  Studies on the Biodiversity of Halophilic Microorganisms Isolated from El-Djerid Salt Lake (Tunisia) under Aerobic Conditions 
Bacterial and archaeal aerobic communities were recovered from sediments from the shallow El-Djerid salt lake in Tunisia, and their salinity gradient distribution was established. Six samples for physicochemical and microbiological analyses were obtained from 6 saline sites in the lake for physico-chemical and microbiological analyses. All samples studied were considered hypersaline with NaCl concentration ranging from 150 to 260 g/L. A specific halophilic microbial community was recovered from each site, and characterization of isolated microorganisms was performed via both phenotypic and phylogenetic approaches. Only one extreme halophilic organism, domain Archaea, was isolated from site 4 only, whereas organisms in the domain Bacteria were recovered from the five remaining sampling sites that contained up to 250 g/L NaCl. Members of the domain Bacteria belonged to genera Salicola, Pontibacillus, Halomonas, Marinococcus, and Halobacillus, whereas the only member of domain Archaea isolated belonged to the genus Halorubrum. The results of this study are discussed in terms of the ecological significance of these microorganisms in the breakdown of organic matter in Lake El-Djerid and their potential for industry applications.
doi:10.1155/2009/731786
PMCID: PMC2804050  PMID: 20066169
9.  Recent studies in microbial degradation of petroleum hydrocarbons in hypersaline environments 
Many hypersaline environments are often contaminated with petroleum compounds. Among these, oil and natural gas production sites all over the world and hundreds of kilometers of coastlines in the more arid regions of Gulf countries are of major concern due to the extent and magnitude of contamination. Because conventional microbiological processes do not function well at elevated salinities, bioremediation of hypersaline environments can only be accomplished using high salt-tolerant microorganisms capable of degrading petroleum compounds. In the last two decades, there have been many reports on the biodegradation of hydrocarbons in moderate to high salinity environments. Numerous microorganisms belonging to the domain Bacteria and Archaea have been isolated and their phylogeny and metabolic capacity to degrade a variety of aliphatic and aromatic hydrocarbons in varying salinities have been demonstrated. This article focuses on our growing understanding of bacteria and archaea responsible for the degradation of hydrocarbons under aerobic conditions in moderate to high salinity conditions. Even though organisms belonging to various genera have been shown to degrade hydrocarbons, members of the genera Halomonas Alcanivorax, Marinobacter, Haloferax, Haloarcula, and Halobacterium dominate the published literature. Despite rapid advances in understanding microbial taxa that degrade hydrocarbons under aerobic conditions, not much is known about organisms that carry out similar processes in anaerobic conditions. Also, information on molecular mechanisms and pathways of hydrocarbon degradation in high salinity is scarce and only recently there have been a few reports describing genes, enzymes and breakdown steps for some hydrocarbons. These limited studies have clearly revealed that degradation of oxygenated and non-oxygenated hydrocarbons by halophilic and halotolerant microorganisms occur by pathways similar to those found in non-halophiles.
doi:10.3389/fmicb.2014.00173
PMCID: PMC4005966  PMID: 24795705
hypersaline environments; biodegradation; oxygenated and non-oxygenated hydrocarbons; halophilic and halotolerant bacteria and archaea; molecular mechanism of degradation
10.  Properties of Halococcus salifodinae, an Isolate from Permian Rock Salt Deposits, Compared with Halococci from Surface Waters 
Life : Open Access Journal  2013;3(1):244-259.
Halococcus salifodinae BIpT DSM 8989T, an extremely halophilic archaeal isolate from an Austrian salt deposit (Bad Ischl), whose origin was dated to the Permian period, was described in 1994. Subsequently, several strains of the species have been isolated, some from similar but geographically separated salt deposits. Hcc. salifodinae may be regarded as one of the most ancient culturable species which existed already about 250 million years ago. Since its habitat probably did not change during this long period, its properties were presumably not subjected to the needs of mutational adaptation. Hcc. salifodinae and other isolates from ancient deposits would be suitable candidates for testing hypotheses on prokaryotic evolution, such as the molecular clock concept, or the net-like history of genome evolution. A comparison of available taxonomic characteristics from strains of Hcc. salifodinae and other Halococcus species, most of them originating from surface waters, is presented. The cell wall polymer of Hcc. salifodinae was examined and found to be a heteropolysaccharide, similar to that of Hcc. morrhuae. Polyhydroxyalkanoate granules were present in Hcc. salifodinae, suggesting a possible lateral gene transfer before Permian times.
doi:10.3390/life3010244
PMCID: PMC4187196  PMID: 25371342
Halococcus species; Halococcus salifodinae; haloarchaea; Permian salt deposit; cell wall polymer; polyhydroxyalkanoate; prokaryotic evolution
11.  Genomic and phenotypic attributes of novel salinivibrios from stromatolites, sediment and water from a high altitude lake 
BMC Genomics  2014;15(1):473.
Background
Salinivibrios are moderately halophilic bacteria found in salted meats, brines and hypersaline environments. We obtained three novel conspecific Salinivibrio strains closely related to S. costicola, from Socompa Lake, a high altitude hypersaline Andean lake (approx. 3,570 meters above the sea level).
Results
The three novel Salinivibrio spp. were extremely resistant to arsenic (up to 200 mM HAsO42−), NaCl (up to 15%), and UV-B radiation (19 KJ/m2, corresponding to 240 minutes of exposure) by means of phenotypic tests. Our subsequent draft genome ionsequencing and RAST-based genome annotation revealed the presence of genes related to arsenic, NaCl, and UV radiation resistance. The three novel Salinivibrio genomes also had the xanthorhodopsin gene cluster phylogenetically related to Marinobacter and Spiribacter. The genomic taxonomy analysis, including multilocus sequence analysis, average amino acid identity, and genome-to-genome distance revealed that the three novel strains belong to a new Salinivibrio species.
Conclusions
Arsenic resistance genes, genes involved in DNA repair, resistance to extreme environmental conditions and the possible light-based energy production, may represent important attributes of the novel salinivibrios, allowing these microbes to thrive in the Socompa Lake.
Electronic supplementary material
The online version of this article (doi:10.1186/1471-2164-15-473) contains supplementary material, which is available to authorized users.
doi:10.1186/1471-2164-15-473
PMCID: PMC4094778  PMID: 24927949
Arsenic; Salinity; UV radiation; Xanthorhodopsin; Extreme environment
12.  Diversity of Bacillus-like organisms isolated from deep-sea hypersaline anoxic sediments 
Saline Systems  2008;4:8.
Background
The deep-sea, hypersaline anoxic brine lakes in the Mediterranean are among the most extreme environments on earth, and in one of them, the MgCl2-rich Discovery basin, the presence of active microbes is equivocal. However, thriving microbial communities have been detected especially in the chemocline between deep seawater and three NaCl-rich brine lakes, l'Atalante, Bannock and Urania. By contrast, the microbiota of these brine-lake sediments remains largely unexplored.
Results
Eighty nine isolates were obtained from the sediments of four deep-sea, hypersaline anoxic brine lakes in the Eastern Mediterranean Sea: l'Atalante, Bannock, Discovery and Urania basins. This culture collection was dominated by representatives of the genus Bacillus and close relatives (90% of all isolates) that were investigated further. Physiological characterization of representative strains revealed large versatility with respect to enzyme activities or substrate utilization. Two third of the isolates did not grow at in-situ salinities and were presumably present as endospores. This is supported by high numbers of endospores in Bannock, Discovery and Urania basins ranging from 3.8 × 105 to 1.2 × 106 g-1 dw sediment. However, the remaining isolates were highly halotolerant growing at salinities of up to 30% NaCl. Some of the novel isolates affiliating with the genus Pontibacillus grew well under anoxic conditions in sulfidic medium by fermentation or anaerobic respiration using dimethylsulfoxide or trimethylamine N-oxide as electron acceptor.
Conclusion
Some of the halophilic, facultatively anaerobic relatives of Bacillus appear well adapted to life in this hostile environment and suggest the presence of actively growing microbial communities in the NaCl-rich, deep-sea brine-lake sediments.
doi:10.1186/1746-1448-4-8
PMCID: PMC2464584  PMID: 18541011
13.  Comparative analysis of ribonuclease P RNA structure in Archaea. 
Nucleic Acids Research  1996;24(7):1252-1259.
Although the structure of the catalytic RNA component of ribonuclease P has been well characterized in Bacteria, it has been little studied in other organisms, such as the Archaea. We have determined the sequences encoding RNase P RNA in eight euryarchaeal species: Halococcus morrhuae, Natronobacterium gregoryi, Halobacterium cutirubrum, Halobacteriurn trapanicum, Methanobacterium thermoautotrophicum strains deltaH and Marburg, Methanothermus fervidus and Thermococcus celer strain AL-1. On the basis of these and previously available sequences from Sulfolobus acidocaldarius, Haloferax volcanii and Methanosarcina barkeri the secondary structure of RNase P RNA in Archaea has been analyzed by phylogenetic comparative analysis. The archaeal RNAs are similar in both primary and secondary structure to bacterial RNase P RNAs, but unlike their bacterial counterparts these archaeal RNase P RNAs are not by themselves catalytically proficient in vitro.
PMCID: PMC145784  PMID: 8614627
14.  Phylogenetic analyses of some extremely halophilic archaea isolated from Dead Sea water, determined on the basis of their 16S rRNA sequences. 
Applied and Environmental Microbiology  1996;62(10):3779-3786.
Twenty-two extremely halophilic aerobic archaeal strains were isolated from enrichments prepared from Dead Sea water samples collected 57 years ago. The isolates were phenotypically clustered into five different groups, and a representative from each group was chosen for further study. Almost the entire sequences of the 16S rRNA genes of these representatives, and of Haloarcula hispanica ATCC 33960, were determined to establish their phylogenetic positions. The sequences of these strains were compared to previously published sequences of 27 reference halophilic archaea (members of the family Halobacteriaceae) and two other archaea, Methanobacterium formicicum DSM 1312 and Methanospirillum hungatei DSM 864. Phylogenetic analysis using approximately 1,400 base comparisons of 16S rRNA-encoding gene sequences demonstrated that the five isolates clustered closely to species belonging to three different genera--Haloferax, Halobacterium, and Haloarcula. Strains E1 and E8 were closely related and identified as members of the species Haloferax volcanii, and strain E12 was closely related and identified as a member of the species Halobacterium salinarum. However, strains E2 and E11 clustered in the Haloarcula branch with Haloarcula hispanica as the closest relative at 98.9 and 98.8% similarity, respectively. Strains E2 and E11 could represent two new species of the genus Haloarcula. However, because strains of these two new species were isolated from a single source, they will not be named until additional strains are isolated from other sources and fully characterized.
PMCID: PMC168186  PMID: 8837434
15.  Subglacial Lake Vostok (Antarctica) Accretion Ice Contains a Diverse Set of Sequences from Aquatic, Marine and Sediment-Inhabiting Bacteria and Eukarya 
PLoS ONE  2013;8(7):e67221.
Lake Vostok, the 7th largest (by volume) and 4th deepest lake on Earth, is covered by more than 3,700 m of ice, making it the largest subglacial lake known. The combination of cold, heat (from possible hydrothermal activity), pressure (from the overriding glacier), limited nutrients and complete darkness presents extreme challenges to life. Here, we report metagenomic/metatranscriptomic sequence analyses from four accretion ice sections from the Vostok 5G ice core. Two sections accreted in the vicinity of an embayment on the southwestern end of the lake, and the other two represented part of the southern main basin. We obtained 3,507 unique gene sequences from concentrates of 500 ml of 0.22 µm-filtered accretion ice meltwater. Taxonomic classifications (to genus and/or species) were possible for 1,623 of the sequences. Species determinations in combination with mRNA gene sequence results allowed deduction of the metabolic pathways represented in the accretion ice and, by extension, in the lake. Approximately 94% of the sequences were from Bacteria and 6% were from Eukarya. Only two sequences were from Archaea. In general, the taxa were similar to organisms previously described from lakes, brackish water, marine environments, soil, glaciers, ice, lake sediments, deep-sea sediments, deep-sea thermal vents, animals and plants. Sequences from aerobic, anaerobic, psychrophilic, thermophilic, halophilic, alkaliphilic, acidophilic, desiccation-resistant, autotrophic and heterotrophic organisms were present, including a number from multicellular eukaryotes.
doi:10.1371/journal.pone.0067221
PMCID: PMC3700977  PMID: 23843994
16.  The Microbial Sulfur Cycle at Extremely Haloalkaline Conditions of Soda Lakes 
Soda lakes represent a unique ecosystem with extremely high pH (up to 11) and salinity (up to saturation) due to the presence of high concentrations of sodium carbonate in brines. Despite these double extreme conditions, most of the lakes are highly productive and contain a fully functional microbial system. The microbial sulfur cycle is among the most active in soda lakes. One of the explanations for that is high-energy efficiency of dissimilatory conversions of inorganic sulfur compounds, both oxidative and reductive, sufficient to cope with costly life at double extreme conditions. The oxidative part of the sulfur cycle is driven by chemolithoautotrophic haloalkaliphilic sulfur-oxidizing bacteria (SOB), which are unique for soda lakes. The haloalkaliphilic SOB are present in the surface sediment layer of various soda lakes at high numbers of up to 106 viable cells/cm3. The culturable forms are so far represented by four novel genera within the Gammaproteobacteria, including the genera Thioalkalivibrio, Thioalkalimicrobium, Thioalkalispira, and Thioalkalibacter. The latter two were only found occasionally and each includes a single species, while the former two are widely distributed in various soda lakes over the world. The genus Thioalkalivibrio is the most physiologically diverse and covers the whole spectrum of salt/pH conditions present in soda lakes. Most importantly, the dominant subgroup of this genus is able to grow in saturated soda brines containing 4 M total Na+ – a so far unique property for any known aerobic chemolithoautotroph. Furthermore, some species can use thiocyanate as a sole energy source and three out of nine species can grow anaerobically with nitrogen oxides as electron acceptor. The reductive part of the sulfur cycle is active in the anoxic layers of the sediments of soda lakes. The in situ measurements of sulfate reduction rates and laboratory experiments with sediment slurries using sulfate, thiosulfate, or elemental sulfur as electron acceptors demonstrated relatively high sulfate reduction rates only hampered by salt-saturated conditions. However, the highest rates of sulfidogenesis were observed not with sulfate, but with elemental sulfur followed by thiosulfate. Formate, but not hydrogen, was the most efficient electron donor with all three sulfur electron acceptors, while acetate was only utilized as an electron donor under sulfur-reducing conditions. The native sulfidogenic populations of soda lakes showed a typical obligately alkaliphilic pH response, which corresponded well to the in situ pH conditions. Microbiological analysis indicated a domination of three groups of haloalkaliphilic autotrophic sulfate-reducing bacteria belonging to the order Desulfovibrionales (genera Desulfonatronovibrio, Desulfonatronum, and Desulfonatronospira) with a clear tendency to grow by thiosulfate disproportionation in the absence of external electron donor even at salt-saturating conditions. Few novel representatives of the order Desulfobacterales capable of heterotrophic growth with volatile fatty acids and alcohols at high pH and moderate salinity have also been found, while acetate oxidation was a function of a specialized group of haloalkaliphilic sulfur-reducing bacteria, which belong to the phylum Chrysiogenetes.
doi:10.3389/fmicb.2011.00044
PMCID: PMC3128939  PMID: 21747784
sulfur-oxidizing bacteria; sulfidogenesis; sulfate-reducing bacteria; sulfur reduction; thiosulfate reduction; soda lakes
17.  Genomes of “Spiribacter”, a streamlined, successful halophilic bacterium 
BMC Genomics  2013;14:787.
Background
Thalassosaline waters produced by the concentration of seawater are widespread and common extreme aquatic habitats. Their salinity varies from that of sea water (ca. 3.5%) to saturation for NaCl (ca. 37%). Obviously the microbiota varies dramatically throughout this range. Recent metagenomic analysis of intermediate salinity waters (19%) indicated the presence of an abundant and yet undescribed gamma-proteobacterium. Two strains belonging to this group have been isolated from saltern ponds of intermediate salinity in two Spanish salterns and were named “Spiribacter”.
Results
The genomes of two isolates of “Spiribacter” have been fully sequenced and assembled. The analysis of metagenomic datasets indicates that microbes of this genus are widespread worldwide in medium salinity habitats representing the first ecologically defined moderate halophile. The genomes indicate that the two isolates belong to different species within the same genus. Both genomes are streamlined with high coding densities, have few regulatory mechanisms and no motility or chemotactic behavior. Metabolically they are heterotrophs with a subgroup II xanthorhodopsin as an additional energy source when light is available.
Conclusions
This is the first bacterium that has been proven by culture independent approaches to be prevalent in hypersaline habitats of intermediate salinity (half a way between the sea and NaCl saturation). Predictions from the proteome and analysis of transporter genes, together with a complete ectoine biosynthesis gene cluster are consistent with these microbes having the salt-out-organic-compatible solutes type of osmoregulation. All these features are also consistent with a well-adapted fully planktonic microbe while other halophiles with more complex genomes such as Salinibacter ruber might have particle associated microniches.
doi:10.1186/1471-2164-14-787
PMCID: PMC3832224  PMID: 24225341
Halophilic bacteria; Xanthorhodopsin; Hypersaline; Saltern; Spiribacter; Moderate halophile
18.  Structural Basis for the Aminoacid Composition of Proteins from Halophilic Archea 
PLoS Biology  2009;7(12):e1000257.
In order to survive in highly saline environments, proteins from halophilic archea have evolved with biased amino acid compositions that have the capacity to reduce contacts with the solvent.
Proteins from halophilic organisms, which live in extreme saline conditions, have evolved to remain folded at very high ionic strengths. The surfaces of halophilic proteins show a biased amino acid composition with a high prevalence of aspartic and glutamic acids, a low frequency of lysine, and a high occurrence of amino acids with a low hydrophobic character. Using extensive mutational studies on the protein surfaces, we show that it is possible to decrease the salt dependence of a typical halophilic protein to the level of a mesophilic form and engineer a protein from a mesophilic organism into an obligate halophilic form. NMR studies demonstrate complete preservation of the three-dimensional structure of extreme mutants and confirm that salt dependency is conferred exclusively by surface residues. In spite of the statistically established fact that most halophilic proteins are strongly acidic, analysis of a very large number of mutants showed that the effect of salt on protein stability is largely independent of the total protein charge. Conversely, we quantitatively demonstrate that halophilicity is directly related to a decrease in the accessible surface area.
Author Summary
Life on earth exhibits an enormous adaptive capacity and living organisms can be found even in extreme environments. The halophilic archea are a group of microorganisms that grow best in highly salted lakes (with KCl concentrations between 2 and 6 molar). To avoid osmotic shock, halophilic archea have the same ionic strength inside their cells as outside. All their macromolecules, including the proteins, have therefore adapted to remain folded and functional under such ionic strength conditions. As a result, the amino acid composition of proteins adapted to a hypersaline environment is very characteristic: they have an abundance of negatively charged residues combined with a low frequency of lysines. In this study, we have investigated the relationship between this biased amino-acid composition and protein stability. Three model proteins – one from a strict halophile, its homolog from a mesophile and a totally unrelated protein from a mesophile - have been largely redesigned by site-directed mutagenesis, and the resulting mutants have been characterized structurally and thermodynamically. Our results show that amino acids with short side-chains (like aspartic and glutamic acid) are preferred to the longer lysine because they succeed in reducing the interaction surface between the protein and the solvent, which is beneficial in an environment where water is in limited availability because it also has to hydrate the salt ions.
doi:10.1371/journal.pbio.1000257
PMCID: PMC2780699  PMID: 20016684
19.  Anaerobic bacteria from hypersaline environments. 
Microbiological Reviews  1994;58(1):27-38.
Strictly anaerobic halophiles, namely fermentative, sulfate-reducing, homoacetogenic, phototrophic, and methanogenic bacteria are involved in the oxidation of organic carbon in hypersaline environments. To date, six anaerobic fermentative genera, containing nine species, have been described. Two of them are homoacetogens. Six species belong to the family Haloanaerobiaceae, as indicated by their unique 16S rRNA oligonucleotide sequences. Desulfohalobium retbaense and Desulfovibrio halophilus represent the only two moderately halophilic sulfate reducers so far reported. Among anoxygenic phototrophic anaerobes, a few purple bacteria with optimal growth at salinities between 6 and 11% NaCl have been isolated from hypersaline habitats. They belong to the genera Rhodospirillum, Chromatium, Thiocapsa, and Ectothiorhodospira. The commonest organisms isolated so far are Chromatium salexigens, Thiocapsa halophila, and Rhodospirillum salinarum. Extremely halophilic purple bacteria have most commonly been isolated from alkaline brines and require about 20 to 25% NaCl for optimal growth. They belong to the family Ectothiorodhospiraceae. Their osmoregulation involves synthesis or uptake of compatible solutes such as glycine-betaine that accumulate in their cytoplasm. The existence of methanogens in hypersaline environments is related to the presence of noncompetitive substrates such as methylamines, which originate mainly from the breakdown of osmoregulatory amines. Methanogenesis probably does not contribute to the mineralization of carbohydrates at NaCl concentrations higher than 15%. Above this concentration, sulfate reduction is probably the main way to oxidize H2 (although at rates too low to use up all the H2 formed) and occupies a terminal function kn the degradation of carbohydrates. Three genera and five species of halophilic methylotrophic methanogens have been reported. A bloom of phototrophic bacteria in the marine salterns of Salins-de-Giraud, located on the Mediterranean French coast in the Rhone Delta, is also described.
PMCID: PMC372951  PMID: 8177169
20.  Synchronous Effects of Temperature, Hydrostatic Pressure, and Salinity on Growth, Phospholipid Profiles, and Protein Patterns of Four Halomonas Species Isolated from Deep-Sea Hydrothermal- Vent and Sea Surface Environments 
Applied and Environmental Microbiology  2004;70(10):6220-6229.
Four strains of euryhaline bacteria belonging to the genus Halomonas were tested for their response to a range of temperatures (2, 13, and 30°C), hydrostatic pressures (0.1, 7.5, 15, 25, 35, 45, and 55 MPa), and salinities (4, 11, and 17% total salts). The isolates were psychrotolerant, halophilic to moderately halophilic, and piezotolerant, growing fastest at 30°C, 0.1 MPa, and 4% total salts. Little or no growth occurred at the highest hydrostatic pressures tested, an effect that was more pronounced with decreasing temperatures. Growth curves suggested that the Halomonas strains tested would grow well in cool to warm hydrothermal-vent and associated subseafloor habitats, but poorly or not at all under cold deep-sea conditions. The intermediate salinity tested enhanced growth under certain high-hydrostatic-pressure and low-temperature conditions, highlighting a synergistic effect on growth for these combined stresses. Phospholipid profiles obtained at 30°C indicated that hydrostatic pressure exerted the dominant control on the degree of lipid saturation, although elevated salinity slightly mitigated the increased degree of lipid unsaturation caused by increased hydrostatic pressure. Profiles of cytosolic and membrane proteins of Halomonas axialensis and H. hydrothermalis performed at 30°C under various salinities and hydrostatic pressure conditions indicated several hydrostatic pressure and salinity effects, including proteins whose expression was induced by either an elevated salinity or hydrostatic pressure, but not by a combination of the two. The interplay between salinity and hydrostatic pressure on microbial growth and physiology suggests that adaptations to hydrostatic pressure and possibly other stresses may partially explain the euryhaline phenotype of members of the genus Halomonas living in deep-sea environments.
doi:10.1128/AEM.70.10.6220-6229.2004
PMCID: PMC522137  PMID: 15466569
21.  Desulfonatronovibrio halophilus sp. nov., a novel moderately halophilic sulfate-reducing bacterium from hypersaline chloride–sulfate lakes in Central Asia 
Extremophiles  2012;16(3):411-417.
Four strains of lithotrophic sulfate-reducing bacteria (SRB) have been enriched and isolated from anoxic sediments of hypersaline chloride–sulfate lakes in the Kulunda Steppe (Altai, Russia) at 2 M NaCl and pH 7.5. According to the 16S rRNA gene sequence analysis, the isolates were closely related to each other and belonged to the genus Desulfonatronovibrio, which, so far, included only obligately alkaliphilic members found exclusively in soda lakes. The isolates utilized formate, H2 and pyruvate as electron donors and sulfate, sulfite and thiosulfate as electron acceptors. In contrast to the described species of the genus Desulfonatronovibrio, the salt lake isolates could only tolerate high pH (up to pH 9.4), while they grow optimally at a neutral pH. They belonged to the moderate halophiles growing between 0.2 and 2 M NaCl with an optimum at 0.5 M. On the basis of their distinct phenotype and phylogeny, the described halophilic SRB are proposed to form a novel species within the genus Desulfonatronovibrio, D. halophilus (type strain HTR1T = DSM24312T = UNIQEM U802T).
Electronic supplementary material
The online version of this article (doi:10.1007/s00792-012-0440-5) contains supplementary material, which is available to authorized users.
doi:10.1007/s00792-012-0440-5
PMCID: PMC3346931  PMID: 22488572
Sulfate-reducing bacteria (SRB); Desulfonatronovibrio; Hypersaline lakes; Halophilic; Life Sciences; Ecology; Biotechnology; Microbiology
22.  Endospores of halophilic bacteria of the family Bacillaceae isolated from non-saline Japanese soil may be transported by Kosa event (Asian dust storm) 
Saline Systems  2005;1:8.
Background
Generally, extremophiles have been deemed to survive in the extreme environments to which they had adapted to grow. Recently many extremophiles have been isolated from places where they are not expected to grow. Alkaliphilic microorganisms have been isolated from acidic soil samples with pH 4.0, and thermophiles have been isolated from samples of low temperature. Numerous moderately halophilic microorganisms, defined as those that grow optimally in media containing 0.5–2.5 Molar (3–15%) NaCl, and halotolerant microorganisms that are able to grow in media without added NaCl and in the presence of high NaCl have been isolated from saline environments such as salterns, salt lakes and sea sands. It has tacitly been believed that habitats of halophiles able to grow in media containing more than 20% (3.4 M) are restricted to saline environments, and no reports have been published on the isolation of halophiles from ordinary garden soil samples.
Results
We demonstrated that many halophilic bacteria that are able to grow in the presence of 20% NaCl are inhabiting in non-saline environments such as ordinary garden soils, yards, fields and roadways in an area surrounding Tokyo, Japan. Analyses of partial 16S rRNA gene sequences of 176 isolates suggested that they were halophiles belonging to genera of the family Bacillaceae, Bacillus (11 isolates), Filobacillus (19 isolates), Gracilibacillus (6 isolates), Halobacillus (102 isolates), Lentibacillus (1 isolate), Paraliobacillus (5 isolates) and Virgibacillus (17 isolates). Sequences of 15 isolates showed similarities less than 92%, suggesting that they may represent novel taxa within the family Bacillaceae.
Conclusion
The numbers of total bacteria of inland soil samples were in a range from 1.4 × 107/g to 1.1 × 106/g. One tenth of the total bacteria was occupied by endospore-forming bacteria. Only very few of the endospore-forming bacteria, roughly 1 out of 20,000, are halophilic bacteria. Most of the halophilic bacteria were surviving as endospores in the soil samples, in a range of less than 1 to about 500/g soil. Samples collected from seashore in a city confronting Tokyo Bay gave the total numbers of bacteria and endospores roughly 1000 time smaller than those of inland soil samples. Numbers of halophilic bacteria per gram, however, were almost the same as those of inland soil samples. A possible source of the halophilic endospore originating from Asian dust storms is discussed.
doi:10.1186/1746-1448-1-8
PMCID: PMC1283985  PMID: 16242015
23.  Distribution and Diversity of Archaea Corresponding to the Limnological Cycle of a Hypersaline Stratified Lake (Solar Lake, Sinai, Egypt) 
The vertical and seasonal distribution and diversity of archaeal sequences was investigated in a hypersaline, stratified, monomictic lake, Solar Lake, Sinai, Egypt, during the limnological development of stratification and mixing. Archaeal sequences were studied via phylogenetic analysis of 16S rDNA sequences as well as denaturing gradient gel electrophoresis analysis. The 165 clones studied were grouped into four phylogenetically different clusters. Most of the clones isolated from both the aerobic epilimnion and the sulfide-rich hypolimnion were defined as cluster I, belonging to the Halobacteriaceae family. The three additional clusters were all isolated from the anaerobic hypolimnion. Cluster II is phylogenetically located between the genera Methanobacterium and Methanococcus. Clusters III and IV relate to two previously documented groups of uncultured euryarchaeota, remotely related to the genus Thermoplasma. No crenarchaeota were found in the water column of the Solar Lake. The archaeal community in the Solar Lake under both stratified and mixed conditions was dominated by halobacteria in salinities higher than 10%. During stratification, additional clusters, some of which may possibly relate to uncultured halophilic methanogens, were found in the sulfide- and methane-rich hypolimnion.
PMCID: PMC92144  PMID: 10919780
24.  Translation of Henrich Klebahn's 'Damaging agents of the klippfish - a contribution to the knowledge of the salt-loving organisms' 
Saline Systems  2010;6:7.
Background
Henrich Klebahn was a German linguist, mycologist and phytopathologist, who was known as Dr. Dr. h. c. Henrich Klebahn, Hauptcustos a. D., Honorarprofessor an der Hanischen Universität. He was born February 20, 1859 in Bremen, and died October 5, 1942 in Hamburg. He taught linguistics from 1885-1899, studied Natural Science at the Universities of Jena and Berlin (1881) and received his PhD from the University of Jena. In 1899, he was appointed scientific assistant at the Hamburg botanical garden, where he worked until 1905. From 1905 to 1930, he was at the agricultural institute of Bromberg. In 1921, he was named honorary professor and lecturer in cryptogams and soil biology at the Institut für Allgemeine Botanik where he taught until 1934. He is well known for his work on gas vesicles and halophiles, among other topics.
This re-print of 'Die Schädlinge des Klippfisches. Ein Beitrag zur Kenntnis der salzliebenden Organismen. Von H. Klebahn. Mit zwei Tafeln und vier Abbildungen im Text.' was originally published in 1919 in the Jahrbuch der Hamb. Wissensch. Anstaltes. XXXVI. Beiheft pages 11-69, by Latcke & Waltt, E. H. Buchdrucker. The translators have tried to remain faithful to the contents and to the original sense of the article by minimizing modifications.
Results
The original paper reported the conclusions of a 3 year long study of the microbes causing damage to the fish industry as well as a summation of work on the subject up until 1919. The findings were that the causative agents were fungi and other microbes, the chief of which was a red, Gram-negative rod-shaped bacillus, Bacillus halobius ruber, that formed pale reddish colonies and was found to oscillate, but after extensive testing, was found not possess flagella. The initial appearance of "a shiny corpuscle" at the ends of cells was determined not to be spores; rather that it was the "result of the coherence of the light beams due to a total reflection of the light in the optically denser little rods". The cells were osmotically sensitive to the addition of water. In addition, a Gram-negative, red Sarcina morrhuae that appeared pinker in color, was less salt-sensitive than the red bacillus, in fact surviving the transfer to water. These were "round individual cells or groups of only two or four cells, usually; however, there are eight or more round cells that are arranged like cube corners to great cube-like or irregular packages lying together, just in the same manner as with the familiar Sarcina ventriculi." This organism was also identified from the walls of a fish storage room. Finally, a third, red microorganism was isolated: a Gram-negative micrococcus, Micrococcus (Diplococcus) morrhuae, which was "spherically rounded" and barely sensitive to water: "If one distributes a sample of a colony in water, the cells partly separate, to a great degree; however, they stay together in groups of two or four cells."
Conclusions
This article provides evidence for identification of halophilic microbes as the major cause of fish spoilage, and is one of the earliest publications in the field of halophile microbiology.
doi:10.1186/1746-1448-6-7
PMCID: PMC2912921  PMID: 20569477
25.  Niche adaptation by expansion and reprogramming of general transcription factors 
Experimental analysis of TFB family proteins in a halophilic archaeon reveals complex environment-dependent fitness contributions. Gene conversion events among these proteins can generate novel niche adaptation capabilities, a process that may have contributed to archaeal adaptation to extreme environments.
Evolution of archaeal lineages correlate with duplication events in the TFB family.Each TFB is required for adaptation to multiple environments.The relative fitness contributions of TFBs change with environmental context.Changes in the regulation of duplicated TFBs can generate new adaptation capabilities.
The evolutionary success of an organism depends on its ability to continually adapt to changes in the patterns of constant, periodic, and transient challenges within its environment. This process of ‘niche adaptation' requires reprogramming of the organism's environmental response networks by reorganizing interactions among diverse parts including environmental sensors, signal transducers, and transcriptional and post-transcriptional regulators. Gene duplications have been discovered to be one of the principal strategies in this process, especially for reprogramming of gene regulatory networks (GRNs). Whereas eukaryotes require dozens of factors for recruitment of RNA polymerase, archaea require just two general transcription factors (GTFs) that are orthologous to eukaryotic TFIIB (TFB in archaea) and TATA-binding protein (TBP) (Bell et al, 1998). Both of these GTFs have expanded extensively in nearly 50% of all archaea whose genomes have been fully sequenced. The phylogenetic analysis presented in this study reveal lineage-specific expansions of TFBs, suggesting that they might encode functionally specialized gene regulatory programs for the unique environments to which these organisms have adapted. This hypothesis is particularly appealing when we consider that the greatest expansion is observed within the group of halophilic archaea whose habitats are associated with routine and dynamic changes in a number of environmental factors including light, temperature, oxygen, salinity, and ionic composition (Rodriguez-Valera, 1993; Litchfield, 1998).
We have previously demonstrated that variations in the expanded set of TFBs (a through e) in Halobacterium salinarum NRC-1 manifests at the level of physical interactions within and across the two families, their DNA-binding specificity, their differential regulation in varying environments, and, ultimately, on the large-scale segregation of transcription of all genes into overlapping yet distinct sets of functionally related groups (Facciotti et al, 2007). We have extended findings from this earlier study with a systematic survey of the fitness consequences of perturbing the TFB network of H. salinarum NRC-1 across 17 environments. Notably, each TFB conferred fitness in two or more environmental conditions tested, and the relative fitness contributions (see Table I) of the five TFBs varied significantly by environment. From an evolutionary perspective, the relationships among these fitness landscapes reveal that two classes of TFBs (c/g- and f-type) appear to have played an important role in the evolution of halophilic archaea by overseeing regulation of core physiological capabilities in these organisms. TFBs of the other clades (b/d and a/e) seem to have emerged much more recently through gene duplications or horizontal gene transfers (HGTs) and are being utilized for adaptation to specialized environmental conditions.
We also investigated higher-order functional interactions and relationships among the duplicated TFBs by performing competition experiments and by mapping genetic interactions in different environments. This demonstrated that depending on environmental context, the TFBs have strikingly different functional hierarchies and genetic interactions with one another. This is remarkable as it makes each TFB essential albeit at different times in a dynamically changing environment.
In order to understand the process by which such gene family expansions shape architecture and functioning of a GRN, we performed integrated analysis of phylogeny, physical interactions, regulation, and fitness landscapes of the seven TFBs in H. salinarum NRC-1. This revealed that evolution of both their protein-coding sequence and their promoter has been instrumental in the encoding of environment-specific regulatory programs. Importantly, the convergent and divergent evolution of regulation and binding properties of TFBs suggested that, aside from HGT and random mutations, a third plausible (and perhaps most interesting) mechanism for acquiring a novel TFB variant is through gene conversion. To test this hypothesis, we synthesized a novel TFBx by transferring TFBa/e clade-specific residues to a TFBd backbone, transformed this variant under the control of either the TFBd or the TFBe promoter (PtfbD or PtfbE) into three different host genetic backgrounds (Δura3 (parent), ΔtfbD, and ΔtfbE), and analyzed fitness and gene expression patterns during growth at 25 and 37°C. This showed that gene conversion events spanning the coding sequence and the promoter, environmental context, and genetic background of the host are all extremely influential in the functional integration of a TFB into the GRN. Importantly, this analysis suggested that altering the regulation of an existing set of expanded TFBs might be an efficient mechanism to reprogram the GRN to rapidly generate novel niche adaptation capability. We have confirmed this experimentally by increasing fitness merely by moving tfbE to PtfbD control, and by generating a completely novel phenotype (biofilm-like appearance) by overexpression of tfbE.
Altogether this study clearly demonstrates that archaea can rapidly generate novel niche adaptation programs by simply altering regulation of duplicated TFBs. This is significant because expansions in the TFB family is widespread in archaea, a class of organisms that not only represent 20% of biomass on earth but are also known to have colonized some of the most extreme environments (DeLong and Pace, 2001). This strategy for niche adaptation is further expanded through interactions of the multiple TFBs with members of other expanded TF families such as TBPs (Facciotti et al, 2007) and sequence-specific regulators (e.g. Lrp family (Peeters and Charlier, 2010)). This is analogous to combinatorial solutions for other complex biological problems such as recognition of pathogens by Toll-like receptors (Roach et al, 2005), generation of antibody diversity by V(D)J recombination (Early et al, 1980), and recognition and processing of odors (Malnic et al, 1999).
Numerous lineage-specific expansions of the transcription factor B (TFB) family in archaea suggests an important role for expanded TFBs in encoding environment-specific gene regulatory programs. Given the characteristics of hypersaline lakes, the unusually large numbers of TFBs in halophilic archaea further suggests that they might be especially important in rapid adaptation to the challenges of a dynamically changing environment. Motivated by these observations, we have investigated the implications of TFB expansions by correlating sequence variations, regulation, and physical interactions of all seven TFBs in Halobacterium salinarum NRC-1 to their fitness landscapes, functional hierarchies, and genetic interactions across 2488 experiments covering combinatorial variations in salt, pH, temperature, and Cu stress. This systems analysis has revealed an elegant scheme in which completely novel fitness landscapes are generated by gene conversion events that introduce subtle changes to the regulation or physical interactions of duplicated TFBs. Based on these insights, we have introduced a synthetically redesigned TFB and altered the regulation of existing TFBs to illustrate how archaea can rapidly generate novel phenotypes by simply reprogramming their TFB regulatory network.
doi:10.1038/msb.2011.87
PMCID: PMC3261711  PMID: 22108796
evolution by gene family expansion; fitness; niche adaptation; reprogramming of gene regulatory network; transcription factor B

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