Two species belonging to a novel genus of archaea, designated Picrophilus oshimae and Picrophilus torridus, have been isolated from two different solfataric locations in northern Japan. One habitat harboring both organisms was a dry, extremely acidic soil (pH < 0.5) that was heated by solfataric gases to about 55 degrees C. In the laboratory both species grew heterotrophically on yeast extract and poorly on tryptone under aerobic conditions at temperatures between 45 and 65 degrees C; they grew optimally at 60 degrees C. The pH optimum was 0.7, but growth occurred even around pH 0. Under optimal conditions, the generation time was about 6 h, yielding densities of up to 10(10) cells per ml. The cells were surrounded by a highly filigreed regular tetragonal S-layer, and the core lipids of the membrane were mainly bis-phytanyltetraethers. The 16S rRNA sequences of the two species were about 3% different. The complete 16S rRNA sequence of P. oshimae was 9.3% different from that of the closest relative, Thermoplasma acidophilum. The morphology and physiological properties of the two species characterize Picrophilus as a novel genus that is a member of a novel family within the order Thermoplasmales.
The Archaea are highly diverse in terms of their physiology, metabolism and ecology. Presently, very few molecular characteristics are known that are uniquely shared by either all archaea or the different main groups within archaea. The evolutionary relationships among different groups within the Euryarchaeota branch are also not clearly understood.
We have carried out comprehensive analyses on each open reading frame (ORFs) in the genomes of 11 archaea (3 Crenarchaeota – Aeropyrum pernix, Pyrobaculum aerophilum and Sulfolobus acidocaldarius; 8 Euryarchaeota – Pyrococcus abyssi, Methanococcus maripaludis, Methanopyrus kandleri, Methanococcoides burtonii, Halobacterium sp. NCR-1, Haloquadratum walsbyi, Thermoplasma acidophilum and Picrophilus torridus) to search for proteins that are unique to either all Archaea or for its main subgroups. These studies have identified 1448 proteins or ORFs that are distinctive characteristics of Archaea and its various subgroups and whose homologues are not found in other organisms. Six of these proteins are unique to all Archaea, 10 others are only missing in Nanoarchaeum equitans and a large number of other proteins are specific for various main groups within the Archaea (e.g. Crenarchaeota, Euryarchaeota, Sulfolobales and Desulfurococcales, Halobacteriales, Thermococci, Thermoplasmata, all methanogenic archaea or particular groups of methanogens). Of particular importance is the observation that 31 proteins are uniquely present in virtually all methanogens (including M. kandleri) and 10 additional proteins are only found in different methanogens as well as A. fulgidus. In contrast, no protein was exclusively shared by various methanogen and any of the Halobacteriales or Thermoplasmatales. These results strongly indicate that all methanogenic archaea form a monophyletic group exclusive of other archaea and that this lineage likely evolved from Archaeoglobus. In addition, 15 proteins that are uniquely shared by M. kandleri and Methanobacteriales suggest a close evolutionary relationship between them. In contrast to the phylogenomics studies, a monophyletic grouping of archaea is not supported by phylogenetic analyses based on protein sequences.
The identified archaea-specific proteins provide novel molecular markers or signature proteins that are distinctive characteristics of Archaea and all of its major subgroups. The species distributions of these proteins provide novel insights into the evolutionary relationships among different groups within Archaea, particularly regarding the origin of methanogenesis. Most of these proteins are of unknown function and further studies should lead to discovery of novel biochemical and physiological characteristics that are unique to either all archaea or its different subgroups.
The genes encoding a putative α-glucosidase (aglA) and an α-mannosidase (manA) appear to be physically clustered in the genome of the extreme acidophile Picrophilus torridus, a situation not found previously in any other organism possessing aglA or manA homologs. While archaeal α-glucosidases have been described, no α-mannosidase enzymes from the archaeal kingdom have been reported previously. Transcription start site mapping and Northern blot analysis revealed that despite their colinear orientation and the small intergenic space, the genes are independently transcribed, both producing leaderless mRNA. aglA and manA were cloned and overexpressed in Escherichia coli, and the purified recombinant enzymes were characterized with respect to their physicochemical and biochemical properties. AglA displayed strict substrate specificity and hydrolyzed maltose, as well as longer α-1,4-linked maltooligosaccharides. ManA, on the other hand, hydrolyzed all possible linkage types of α-glycosidically linked mannose disaccharides and was able to hydrolyze α3,α6-mannopentaose, which represents the core structure of many triantennary N-linked carbohydrates in glycoproteins. The probable physiological role of the two enzymes in the utilization of exogenous glycoproteins and/or in the turnover of the organism's own glycoproteins is discussed.
The pathway of glucose degradation in the thermoacidophilic euryarchaeon Picrophilus torridus has been studied by in vivo labeling experiments and enzyme analyses. After growth of P. torridus in the presence of [1-13C]- and [3-13C]glucose, the label was found only in the C-1 and C-3 positions, respectively, of the proteinogenic amino acid alanine, indicating the exclusive operation of an Entner-Doudoroff (ED)-type pathway in vivo. Cell extracts of P. torridus contained all enzyme activities of a nonphosphorylative ED pathway, which were not induced by glucose. Two key enzymes, gluconate dehydratase (GAD) and a novel 2-keto-3-deoxygluconate (KDG)-specific aldolase (KDGA), were characterized. GAD is a homooctamer of 44-kDa subunits, encoded by Pto0485. KDG aldolase, KDGA, is a homotetramer of 32-kDa subunits. This enzyme was highly specific for KDG with up to 2,000-fold-higher catalytic efficiency compared to 2-keto-3-deoxy-6-phosphogluconate (KDPG) and thus differs from the bifunctional KDG/KDPG aldolase, KD(P)GA of crenarchaea catalyzing the conversion of both KDG and KDPG with a preference for KDPG. The KDGA-encoding gene, kdgA, was identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) as Pto1279, and the correct translation start codon, an ATG 24 bp upstream of the annotated start codon of Pto1279, was determined by N-terminal amino acid analysis. The kdgA gene was functionally overexpressed in Escherichia coli. Phylogenetic analysis revealed that KDGA is only distantly related to KD(P)GA, both enzymes forming separate families within the dihydrodipicolinate synthase superfamily. From the data we conclude that P. torridus degrades glucose via a strictly nonphosphorylative ED pathway with a novel KDG-specific aldolase, thus excluding the operation of the branched ED pathway involving a bifunctional KD(P)GA as a key enzyme.
The cryptic high copy number plasmid pRN1 from the thermophilic and acidophilic crenarchaeote Sulfolobus islandicus shares three conserved open reading frames with other S.islandicus plasmids. One of the open reading frames, namely orf80, encodes a 9.5 kDa protein that has no homology to any characterised protein. Recombinant ORF80 purified from Escherichia coli binds to double-stranded DNA in a sequence-specific manner as suggested by EMSA experiments and DNase I footprints. Two highly symmetrical binding sites separated by ∼60 bp were found upstream of the orf80 gene. Both binding sites contain two TTAA motifs as well as other conserved bases. Fluorescence measurements show that short duplex DNAs derived from a single binding site sequence are bound with submicromolar affinity and moderate cooperativity by ORF80. On DNA fragments carrying both binding sites, a rather large protein–DNA complex is formed in a highly cooperative manner. ORF80 contains an N-terminal leucine zipper motif and a highly basic domain at its C-terminus. Compared to all known basic leucine zipper proteins the order of the domains is reversed in ORF80. ORF80 may therefore constitute a new subclass of basic leucine zipper DNA-binding proteins.
There is still a lack of information on the specific characteristics
of DNA-binding proteins from hyperthermophiles. Here we report on
the product of the gene orf56 from plasmid pRN1
of the acidophilic and thermophilic archaeon Sulfolobus
islandicus. orf56 has not been characterised
yet but low sequence similarily to several eubacterial plasmid-encoded genes
suggests that this 6.5 kDa protein is a sequence-specific DNA-binding
protein. The DNA-binding properties of ORF56, expressed in Escherichia coli,
have been investigated by EMSA experiments and by fluorescence anisotropy
measurements. Recombinant ORF56 binds to double-stranded DNA, specifically
to an inverted repeat located within the promoter of orf56.
Binding to this site could down-regulate transcription of the orf56 gene and also of the overlapping orf904 gene,
encoding the putative initiator protein of plasmid replication.
By gel filtration and chemical crosslinking we have shown that ORF56 is
a dimeric protein. Stoichiometric fluorescence anisotropy titrations
further indicate that ORF56 binds as a tetramer to the inverted
repeat of its target binding site. CD spectroscopy points to a significant increase
in ordered secondary structure of ORF56 upon binding DNA. ORF56
binds without apparent cooperativity to its target DNA with a dissociation constant
in the nanomolar range. Quantitative analysis of binding isotherms
performed at various salt concentrations and at different temperatures
indicates that approximately seven ions are released upon complex formation
and that complex formation is accompanied by a change in heat capacity
of –6.2 kJ/mol. Furthermore, recombinant ORF56
proved to be highly thermostable and is able to bind DNA up to 85°C.
A 5-kbp region of pAD1, previously shown to be capable of supporting replication, copy control, and stable inheritance of the plasmid, was cloned into a replicon probe vector and subjected to transposon insertional mutagenesis. Transposon inserts identifying essential replication, copy control, and stability functions were isolated. Deletion of stability functions not essential for replication resulted in delimitation of a basic replicon. The complete DNA sequence of this approximately 3-kbp region and the precise positions of several transposon inserts were determined, and the phenotypic effects of the transposon inserts were correlated with the physical locations of individual determinants. The following three genes, apparently involved in plasmid maintenance, were identified; repA, which encodes a protein required for replication; repB, which encodes a protein involved in copy control; and repC, which may be involved in stable inheritance. In addition, two clusters of repeats composed of a consensus sequence, TAGTARRR, were identified, one located between the divergently transcribed repA and repB genes and another located downstream of repC. The region between repA and repB contained 25 repeats divided into two subregions of 13 and 12 repeats separated by 78 bp. The region located downstream of repC contained only three repeats but may be essential for plasmid replication, since deletion of this determinant resulted in loss of ability to replicate in Enterococcus faecalis. We hypothesize that the repeat units represent protein-binding sites required for assembly of the replisome and control of plasmid copy number. Another region of unrelated repeat units that may also be involved in replication is located within the repA gene. Possible mechanisms of action of these determinants are discussed.
Pantothenate kinase (CoaA) catalyzes the first step of the coenzyme A (CoA) biosynthetic pathway and controls the intracellular concentrations of CoA through feedback inhibition in bacteria. An alternative enzyme found in archaea, pantoate kinase, is missing in the order Thermoplasmatales. The PTO0232 gene from Picrophilus torridus, a thermoacidophilic euryarchaeon, is shown to be a distant homologue of the prokaryotic type I CoaA. The cloned gene clearly complements the poor growth of the temperature-sensitive Escherichia coli CoaA mutant strain ts9, and the recombinant protein expressed in E. coli cells transfers phosphate to pantothenate at pH 5 and 55°C. In contrast to E. coli CoaA, the P. torridus enzyme is refractory to feedback regulation by CoA, indicating that in P. torridus cells the CoA levels are not regulated by the CoaA step. These data suggest the existence of two subtypes within the class of prokaryotic type I CoaAs.
Two endogenous plasmids are present in Synechococcus elongatus PCC 7942, a model organism for studying photosynthesis and circadian rhythms in cyanobacteria. The large plasmid, pANL, was shown previously to be involved in adaptation of S. elongatus cells to sulfur starvation, which provided the first evidence of cellular function of a cyanobacterial plasmid. Here, we report the complete sequence of pANL, which is 46,366 bp in length with 53% GC content and encodes 58 putative ORFs. The pANL plasmid can be divided into four structural and functional regions: the replication origin region, a signal transduction region, a plasmid maintenance region, and a sulfur-regulated region. Cosmid-based deletion analysis suggested that the plasmid maintenance and replication origin regions are required for persistence of pANL in the cells. Transposon-mediated mutagenesis and complementation-based pANL segregation assays confirmed that two predicted toxin-antitoxin cassettes encoded in the plasmid maintenance region, belonging to PemK and VapC families, respectively, are necessary for plasmid exclusion. The compact and efficient organization of sulfur-related genes on pANL may provide selective advantages in environments with limited sulfur.
Synechococcus elongatus PCC 7942; cyanobacterial plasmid; toxin-antitoxin cassette; plasmid maintenance
Virulence functions of pathogenic bacteria are often encoded on large extrachromosomal plasmids. These plasmids are maintained at low copy number to reduce the metabolic burden on their host. Low-copy-number plasmids risk loss during cell division. This is countered by plasmid-encoded systems that ensure that each cell receives at least one plasmid copy. Plasmid replication and recombination can produce plasmid multimers that hinder plasmid segregation. These are removed by multimer resolution systems. Equitable distribution of the resulting monomers to daughter cells is ensured by plasmid partition systems that actively segregate plasmid copies to daughter cells in a process akin to mitosis in higher organisms. Any plasmid-free cells that still arise due to occasional failures of replication, multimer resolution, or partition are eliminated by plasmid-encoded postsegregational killing systems. Here we argue that all of these three systems are essential for the stable maintenance of large low-copy-number plasmids. Thus, they should be found on all large virulence plasmids. Where available, well-annotated sequences of virulence plasmids confirm this. Indeed, virulence plasmids often appear to contain more than one example conforming to each of the three system classes. Since these systems are essential for virulence, they can be regarded as ubiquitous virulence factors. As such, they should be informative in the search for new antibacterial agents and drug targets.
A multiresistant Klebsiella pneumoniae strain isolated from neonates in Mendoza, Argentina, harbored a 48-kilobase-pair (kbp) plasmid, pMET1, with genetic determinants for resistance to amikacin and also ampicillin, kanamycin, streptomycin, and tobramycin. This plasmid was compared with pJHCMW1, a previously isolated 11-kbp plasmid carrying transposon Tn1331, which encodes resistance to amikacin, as well as ampicillin, kanamycin, streptomycin, and tobramycin, and which was originally present in a K. pneumoniae strain that caused an outbreak in a hospital in Buenos Aires, Argentina. The comparison demonstrated that the replication regions of the two plasmids are unrelated. However, in pMET1 an 11-kbp transposition element, Tn1331.2, was identified; it was closely related to Tn1331, with the difference that a 3-kbp BamHI DNA fragment carrying the aminoglycoside resistance genes was duplicated in tandem.
The gag-pol readthrough mutant of Moloney murine leukemia virus, MLV-B(CAG) (T. Odawara, H. Yoshikura, M. Oshima, T. Tanaka, D. S. Jones, F. Nemoto, Y. Kuchino, and A. Iwamoto, J. Virol. 65:6376–6379, 1991), was poorly complemented by a mutant encoding only Gag. This is because with all the genetic elements necessary for env expression present in MLV-B(CAG), insufficient Env protein was produced by the cells expressing MLV-B(CAG) for efficient virus production. Since the env mRNA expression per provirus in the MLV-B(CAG)- and wild-type-MLV-producing cells were the same and since the cells expressing the former contained eightfold fewer proviral copies, the insufficient Env expression by the former was found to be due to insufficient proviral copies in the cells. Examination of the cell clones having various proviral copies of Δwt MLV (M. Oshima, T. Odawara, T. Matano, H. Sakahira, Y. Kuchino, A. Iwamoto, and H. Yoshikura, J. Virol. 70:2286–2295, 1996) showed that mRNA level was proportional to the number of proviral copies while interference and virus production followed a sigmoid curve with a sharp rise at the threshold number of proviral copies of around four per cell. Multicycle infection probably continues until the threshold level of proviral copies is attained in natural infection too.
The plasmid pRN1 from Sulfolobus islandicus REN1H1 belongs to the crenarchaeal plasmid family pRN. The plasmids in this family encode three conserved proteins that participate in plasmid replication and copy number regulation, as suggested by biochemical characterization of the recombinant proteins. In order to deepen our understanding of the molecular biology of these plasmids, we investigated the transcriptional activity of the model plasmid pRN1. We detected five major transcripts present at about 2 to 15 copies per cell. One long transcriptional unit comprises the genes for the plasmid-copy-number control protein Orf56/CopG and the replication protein Orf904. A second transcript with a long 3′-untranslated region codes for the DNA binding protein Orf80. For both transcripts, we identified countertranscripts which could play a regulatory role. The function of the fifth transcript is unclear. For the five transcripts, we determined the start site, the transcript end, the stability, and the abundance in different growth phases. Reporter gene experiments demonstrated that the copy number control protein Orf56 represses transcription of the orf56-orf904 cotranscript in vivo.
The Enterococcus plasmid pHTβ (63.7 kbp) is a pheromone-independent, highly conjugative pMG1-like plasmid that carries a Tn1546-like transposon encoding vancomycin resistance. The transfer-related regions (Tra I, Tra II, and Tra III) containing oriT and a putative nickase gene (traI) have previously been identified in pHTβ, and in this study, we found that the plasmid conferred the ability to self-aggregate on the host strain Enterococcus faecalis FA2-2. A region where mutation resulted in the impairment of aggregation was identified and mapped to a point upstream of the transfer-related Tra I region. This region consisted of an approximately 6-kbp segment that contained the five open reading frames (ORFs) ORF9 to ORF13. These ORFs are considered to encode the aggregation function, although the precise mode of action of each ORF has not yet been elucidated. An in-frame deletion mutant of ORF10 resulted in reduced aggregation and decreased transfer frequency in broth mating. Transcription analysis of the aggregation region showed that the five ORFs from ORF9 to ORF13 form an operon structure, and a long transcript that started from a promoter region located upstream of ORF9 was identified. Tra II spans a 1.7-kbp region containing ORF56 and ORF57. Tn917-lac insertions into or an in-frame deletion mutant of ORF56 (187 amino acids) resulted in impaired transfer and aggregation. The cloned ORF56 complemented these functions in trans. The transcription levels of ORF10 and ORF13 were reduced in the in-frame mutants of ORF56, but this reduction was complemented by a cloned ORF56 in trans. The results indicated that ORF56 positively regulated the aggregation and plasmid transfer in the host strain, and ORF56 was designated traB.
Sequencing of the genome of Ralstonia solanacearum revealed several genes that putatively code for polyphenol oxidases (PPOs). To study the actual expression of these genes, we looked for and detected all kinds of PPO activities, including laccase, cresolase, and catechol oxidase activities, in cellular extracts of this microorganism. The conditions for the PPO assays were optimized for the phenolic substrate, pH, and sodium dodecyl sulfate concentration used. It was demonstrated that three different PPOs are expressed. The genes coding for the enzymes were unambiguously correlated with the enzymatic activities detected by generation of null mutations in the genes by using insertional mutagenesis with a suicide plasmid and estimating the changes in the levels of enzymatic activities compared to the levels in the wild-type strain. The protein encoded by the RSp1530 locus is a multicopper protein with laccase activity. Two other genes, RSc0337 and RSc1501, code for nonblue copper proteins exhibiting homology to tyrosinases. The product of RSc0337 has strong tyrosine hydroxylase activity, and it has been shown that this enzyme is involved in melanin synthesis by R. solanacearum. The product of the RSc1501 gene is an enzyme that shows a clear preference for oxidation of o-diphenols. Preliminary characterization of the mutants obtained indicated that PPOs expressed by R. solanacearum may participate in resistance to phenolic compounds since the mutants exhibited higher sensitivity to l-tyrosine than the wild-type strain. These results suggest a possible role in the pathogenic process to avoid plant resistance mechanisms involving the participation of phenolic compounds.
Extremophiles are organisms that can grow and thrive in harsh conditions, e.g., extremes of temperature, pH, salinity, radiation, pressure and oxygen tension. Thermophilic, halophilic and radiation-resistant organisms are all microbes, some of which are able to withstand multiple extremes. Psychrophiles, or cold-loving organisms, include not only microbes, but fish that live in polar waters and animals that can withstand freezing. Extremophiles are structurally adapted at a molecular level to withstand these conditions. Thermophiles have particularly stable proteins and cell membranes, psychrophiles have flexible cellular proteins and membranes and/or antifreeze proteins, salt-resistant halophiles contain compatible solutes or high concentrations of inorganic ions, and acidophiles and alkaliphiles are able to pump ions to keep their internal pH close to neutrality. Their interest to veterinary medicine resides in their capacity to be pathogenic, and as sources of enzymes and other molecules for diagnostic and pharmaceutical purposes. In particular, thermostable DNA polymerases are a mainstay of PCR-based diagnostics.
Extremophiles; Adaptation; Thermophiles; Extremozymes; Diagnostics; Polymerase chain reaction
A moderately thermophilic (45 to 50°C), highly acidophilic (pH 1.5 to 2.5), chemolithotrophic Acidithiobacillus caldus strain, f, was isolated from a biooxidation process used to treat nickel ore. Trans-alternating field electrophoresis analysis of total DNA from the A. caldus cells revealed two plasmids of approximately 14 and 45 kb. The 14-kb plasmid, designated pTC-F14, was cloned and shown by replacement of the cloning vector with a kanamycin resistance gene to be capable of autonomous replication in Escherichia coli. Autonomous replication was also demonstrated in Pseudomonas putida and Agrobacterium tumefaciens LBA 4404, which suggested that pTC-F14 is a broad-host-range plasmid. Sequence analysis of the pTC-F14 replicon region revealed five open reading frames and a replicon organization like that of the broad-host-range IncQ plasmids. Three of the open reading frames encoded replication proteins which were most closely related to those of IncQ-like plasmid pTF-FC2 (amino acid sequence identities: RepA, 81%; RepB, 78%; RepC, 74%). However, the two plasmids were fully compatible and pTC-F14 represents a new IncQ-like plasmid replicon. Surprisingly, asymmetrical incompatibility was found with the less closely related IncQ plasmid R300B derivative pKE462 and the IncQ-like plasmid derivative pIE1108. Analysis of the pTC-F14 oriV region revealed five direct repeats consisting of three perfectly conserved 22-bp iterons flanked by iterons of 23 and 21 bp. Plasmid pTC-F14 had a copy number of 12 to 16 copies per chromosome in both E. coli, and A. caldus. The rep gene products of pTC-F14 and pTF-FC2 were unable to functionally complement each other's oriV regions, but replication occurred when the genes for each plasmid's own RepA, RepB, and RepC proteins were provided in trans. Two smaller open reading frames were found between the repB and repA genes of pTC-F14, which encode proteins with high amino acid sequence identity (PasA, 81%; PasB, 72%) to the plasmid addiction system of pTF-FC2. This is the second time a plasmid stability system of this type has been found on an IncQ-like plasmid.
Polyphenol oxidases (PPOs) are copper-containing metalloenzymes encoded in the nucleus and transported into the plastids. Reportedly, PPOs cause time-dependent discoloration (browning) of end-products of wheat and barley, which impairs their appearance quality. For this study, two barley PPO homologues were amplified using PCR with a primer pair designed in the copper binding domains of the wheat PPO genes. The full-lengths of the respective PPO genes were cloned using a BAC library, inverse-PCR, and 3′-RACE. Linkage analysis showed that the polymorphisms in PPO1 and PPO2 co-segregated with the phenol reaction phenotype of awns. Subsequent RT-PCR experiments showed that PPO1 was expressed in hulls and awns, and that PPO2 was expressed in the caryopses. Allelic variation of PPO1 and PPO2 was analysed in 51 barley accessions with the negative phenol reaction of awns. In PPO1, amino acid substitutions of five types affecting functionally important motif(s) or C-terminal region(s) were identified in 40 of the 51 accessions tested. In PPO2, only one mutant allele with a precocious stop codon resulting from an 8 bp insertion in the first exon was found in three of the 51 accessions tested. These observations demonstrate that PPO1 is the major determinant controlling the phenol reaction of awns. Comparisons of PPO1 single mutants and the PPO1PPO2 double mutant indicate that PPO2 controls the phenol reaction in the crease on the ventral side of caryopses. An insertion of a hAT-family transposon in the promoter region of PPO2 may be responsible for different expression patterns of the duplicate PPO genes in barley.
Gene duplication; grasses; Hordeum vulgare; mutant; phenol reaction; PPO
The complete nucleotide sequence of pKDSC50, a large virulence plasmid from Salmonella enterica serovar Choleraesuis strain RF-1, has been determined. We identified 48 of the open reading frames (ORFs) encoded by the 49,503-bp molecule. pKDSC50 encodes a known virulence-associated operon, the spv operon, which is composed of genes essential for systemic infection by nontyphoidal Salmonella. Analysis of the genetic organization of pKDSC50 suggests that the plasmid is composed of several virulence-associated genes, which include the spvRABCD genes, plasmid replication and maintenance genes, and one insertion sequence element. A second virulence-associated region including the pef (plasmid-encoded fimbria) operon and rck (resistance to complement killing) gene, which has been identified on the virulence plasmid of S. enterica serovar Typhimurium, was absent. Two different replicon regions, similar to the RepFIIA and RepFIB replicons, were found. Both showed high similarity to those of the pO157 plasmid of enterohemorrhagic Escherichia coli O157:H7 and the enteropathogenic E. coli (EPEC) adherence factor plasmid harbored by EPEC strain B171 (O111:NM), as well as the virulence plasmids of Salmonella serovars Typhimurium and Enteritidis. Comparative analysis of the nucleotide sequences of the 50-kb virulence plasmid of serovar Choleraesuis and the 94-kb virulence plasmid of serovar Typhimurium revealed that 47 out of 48 ORFs of the virulence plasmid of serovar Choleraesuis are highly homologous to the corresponding ORFs of the virulence plasmid of serovar Typhimurium, suggesting a common ancestry.
Five strains of mesophilic, facultatively organotrophic, ore-leaching eubacteria were isolated from solfatara fields in Iceland and a uranium mine in the Federal Republic of Germany. The new organisms are aerobic gram-negative rods. They can use sulfidic ores or elemental sulfur as sole energy source, indicating that they belong to the genus Thiobacillus. Alternatively, they grow on organic substrates such as yeast extract, peptone, and pyruvate. In contrast to the other leaching bacteria known so far, the new isolates are unable to oxidize ferrous iron. They consist of extreme and moderate acidophiles growing optimally at pH 3 and 4, respectively. The extreme acidophiles showed leaching characteristics similar to those shown by Thiobacillus ferrooxidans, while the moderate acidophiles exhibited a pronounced preference for copper leaching on some chalcopyrite ores. The G+C content of the DNA is between 66 and 69 mol%, depending on the isolate. In DNA-DNA hybridization experiments, the new strains showed homologies among each other of >70%, indicating that they belong to the same species. No significant DNA homology to Thiobacillus reference strains was detectable. Therefore, the new isolates represent a new species of Thiobacillus, which we name Thiobacillus cuprinus. Isolate Hö5 is designated as the type strain (DSM 5495).
Prophenoloxidase (PPO) plays an important role in melanization, necessary for defense against intruding parasitoids. Parasitoids have evolved to inject maternal virulence factors into the host hemocoel to suppress hemolymph melanization for the successful development of their progeny. In this study, the full-length complementary DNA (cDNA) of a Pieris rapae PPO was cloned. Its cDNA contained a 2 076-base pair (bp) open reading frame (ORF) encoding 691 amino acids (aa). Two putative copper-binding sites, a proteolytic activation site, three conserved hemocyanin domains, and a thiol ester motif were found in the deduced amino acid sequence. According to both multiple alignment and phylogenetic analysis, P. rapae PPO gene cloned here is a member of the lepidopteran PPO-2 family. Injection of Cotesia glomerata venom or calyx fluid resulted in reduction of P. rapae hemolymph phenoloxidase activity, demonstrating the ability to inhibit the host′s melanization. Real-time reverse transcriptase polymerase chain reaction (RT-PCR) showed that transcripts of P. rapae PPO-2 in the haemocytes from larvae had not significantly changed following venom injection, suggesting that the regulation of PPO messenger RNA (mRNA) expression by venom was not employed by C. glomerata to cause failure of melanization in parasitized host. While decreased P. rapae PPO-2 gene expression was observed in the haemocytes after calyx fluid injection, no detectable transcriptional change was induced by parasitization, indicating that transcriptional down-regulation of PPO by calyx fluid might play a minor role involved in inhibiting the host′s melanization.
Prophenoloxidase; Cloning; Venom; Calyx fluid; Gene expression; Parasitoid
Three plasmids isolated from the crenarchaeal thermoacidophile
Sulfolobus neozealandicus were characterized.
Plasmids pTAU4 (7,192 bp), pORA1 (9,689 bp) and pTIK4 (13,638 bp) show
unusual properties that distinguish them from previously characterized
cryptic plasmids of the genus Sulfolobus. Plasmids
pORA1 and pTIK4 encode RepA proteins, only the former of which carries
the novel polymerase–primase domain of other known
Sulfolobus plasmids. Plasmid pTAU4 encodes a
mini-chromosome maintenance protein homolog and no RepA protein; the
implications for DNA replication are considered. Plasmid pORA1 is the
first Sulfolobus plasmid to be characterized that
does not encode the otherwise highly conserved DNA-binding PlrA
protein. Another encoded protein appears to be specific for the New
Zealand plasmids. The three plasmids should provide useful model
systems for functional studies of these important crenarchaeal
chemotaxis; crenarchaeal plasmid; DNA replicase; MCM protein
The complete nucleotide sequence and organization of the enteropathogenic Escherichia coli (EPEC) adherence factor (EAF) plasmid of EPEC strain B171 (O111:NM) were determined. The EAF plasmid encodes two known virulence-related operons, the bfp operon, which is composed of genes necessary for biosynthesis of bundle-forming pili, and the bfpTVW (perABC) operon, composed of regulatory genes required for bfp transcription and also for transcriptional activation of the eae gene in the LEE pathogenicity island on the EPEC chromosome. The 69-kb EAF plasmid, henceforth designated pB171, contains, besides the bfp and bfpTVW (perABC) operons, potential virulence-associated genes, plasmid replication and maintenance genes, and many insertion sequence elements. Of the newly identified open reading frames (ORFs), two which comprise a single operon had the potential to encode proteins with high similarity to a C-terminal region of ToxB whose coding sequence is located on pO157, a large plasmid harbored by enterohemorrhagic E. coli. Another ORF, located between the bfp and bfpTVW operons, showed high similarity with trcA, a bfpT-regulated chaperone-like protein gene of EPEC. Two sites were found to be putative replication regions: one similar to RepFIIA of p307 or F, and the other similar to RepFIB of R100 (NR1). In addition, we identified a third region that contains plasmid maintenance genes. Insertion elements were scattered throughout the plasmid, indicating the mosaic nature of the EAF plasmid and suggesting evolutionary events by which virulence genes may have been obtained.
A 3.4-kb cryptic plasmid was obtained from a new isolate of Rhodobacter blasticus. This plasmid, designated pMG160, was mobilizable by the conjugative strain Escherichia coli S17.1 into Rhodobacter sphaeroides, Rhodobacter capsulatus, and Rhodopseudomonas palustris. It replicated in the latter strains but not in Rhodospirillum rubrum, Rhodocyclus gelatinosus, or Bradyrhizobium species. Plasmid pMG160 was stably maintained in R. sphaeroides for more than 100 generations in the absence of selection but showed segregational instability in R. palustris. Instability in R. palustris correlated with a decrease in plasmid copy number compared to the copy number in R. sphaeroides. The complete nucleotide sequence of plasmid pMG160 contained three open reading frames (ORFs). The deduced amino acid sequences encoded by ORF1 and ORF2 showed high degrees of homology to the MobS and MobL proteins that are involved in plasmid mobilization of certain plasmids. Based on homology with the Rep protein of several other plasmids, ORF3 encodes a putative rep gene initiator of plasmid replication. The functions of these sequences were demonstrated by deletion mapping, frameshift analysis, and analysis of point mutations. Two 6.1-kb pMG160-based E. coli-R. sphaeroides shuttle cloning vectors were constructed and designated pMG170 and pMG171. These two novel shuttle vectors were segregationally stable in R. sphaeroides growing under nonselective conditions.
Escherichia coli isolates recovered from patients during a clonal outbreak in a Warsaw, Poland, hospital in 1997 produced different levels of an extended-spectrum β-lactamase (ESBL) of the SHV type. The β-lactamase hyperproduction correlated with the multiplication of ESBL gene copies within a plasmid. Here, we present the complete nucleotide sequence of plasmid p1658/97 carried by the isolates recovered during the outbreak. The plasmid is 125,491 bp and shows a mosaic structure in which all modules constituting the plasmid core are homologous to those found in plasmids F and R100 and are separated by segments of homology to other known regions (plasmid R64, Providencia rettgeri genomic island R391, Vibrio cholerae STX transposon, Klebsiella pneumoniae or E. coli chromosomes). Plasmid p1658/97 bears two replication systems, IncFII and IncFIB; we demonstrated that both are active in E. coli. The presence of an active partition system (sopABC locus) and two postsegregational killing systems (pemIK and hok/sok) indicates that the plasmid should be stably maintained in E. coli populations. The conjugative transfer is ensured by the operons of the tra and trb genes. We also demonstrate that the plasmidic segment undergoing amplification contains the blaSHV-5 gene and is homologous to a 7.9-kb fragment of the K. pneumoniae chromosome. The amplicon displays the structure of a composite transposon of type I.