This study was initiated to explore the emission characteristics of Reduced Sulfur Compounds (RSCs: hydrogen sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide), ammonia and trimethylamine from a Wastewater Treatment Plant (WWTP) located at Sun-Cheon, Chonlanam-Do in South Korea. The study also evaluates flux profiles of the six selected odorous compounds and their flux rates (μg/m2/min) and compares their emission characteristics. A Dynamic Flux Chamber DFC was used to measure fluxes of pollutants from the treatment plant. Quality control of odor samples using a non-reactive sulfur dioxide gas determined the time taken for DFC concentration to reach equilibrium. The reduced sulfur compounds were analyzed by interfacing gas chromatography with a Pulsed Flame Photometric Detector (PFPD). Air samples were collected in the morning and afternoon on one day during summer (August) and two days in winter (December and January). Their emission rates were determined and it was observed that during summer relatively higher amounts of the selected odorous compounds were emitted compared to winter. Air samples from primary settling basin, aeration basin, and final settling basin were tested and the total amount of selected odorous compounds emitted per wastewater ton was found to be 1344 μg/m3 from the selected treatment processes. It was also observed that, in this study, the dominant odor intensity contribution was caused by dimethyl disulfide (69.1%).
Odorous compounds; emission characteristics; Dynamic Flux Chamber (DFC)
A majority of heterotrophic bacteria isolated from soil, water, sediment, vegetation, and marine algae cultures methylated sulfide, producing methanethiol. This was demonstrated with intact cells by measuring the emission of methanethiol with a sulfur-selective chemiluminescence detector, and in cell extracts by detection of sulfide-dependent thiol methyltransferase activity. Extracts of two Pseudomonas isolates were fractionated by gel-filtration and ion-exchange chromatography, and with sulfide as the substrate a single peak of thiol methyltransferase activity was seen in each case. Extracts of several bacterial strains also contained thiol methyltransferase activity with organic thiols as substrates. Thus, S-adenosylmethionine-dependent thiol methyltransferase activities are widespread in bacteria and may contribute to biogenic emissions of methylated sulfur gases and to the production of methyl thioethers.
The vertical distribution of major and intermediate electron acceptors and donors was measured in a shallow stratified fjord. Peaks of zero valence sulfur, Mn(IV), and Fe(III) were observed in the chemocline separating oxic surface waters from sulfidic and anoxic bottom waters. The vertical fluxes of electron acceptors and donors (principally O2 and H2S) balanced within 5%; however, the zones of oxygen reduction and sulfide oxidation were clearly separated. The pathway of electron transfer between O2 and H2S was not apparent from the distribution of sulfur, nitrogen, or metal compounds investigated. The chemical zonation was related to bacterial populations as detected by ethidium bromide (EtBr) staining and by in situ hybridization with fluorescent oligonucleotide probes of increasing specificity. About half of all EtBr-stained cells were detectable with a general oligonucleotide probe for all eubacteria when digital image analysis algorithms were used to improve sensitivity. Both EtBr staining and hybridization indicated a surprisingly uniform distribution of bacteria throughout the water column. However, the average cell size and staining intensity as well as the abundance of different morphotypes changed markedly within the chemocline. The constant overall cell counts thus concealed pronounced population shifts within the water column. Cells stained with a delta 385 probe (presumably sulfate-reducing bacteria) were detected at the chemocline at about 5 x 10(4) cells per ml, and this concentration increased to 2 x 10(5) cells per ml beneath the chemocline. A long slim rod-shaped bacterium was found in large numbers in the oxic part of the chemocline, whereas large ellipsoid cells dominated at greater depth. Application of selective probes for known genera of sulfate-reducing bacteria gave only low cell counts, and thus it was not possible to identify the dominant morphotypes of the sulfate-reducing community.
Achromatium oxaliferum is a large, morphologically conspicuous, sediment-dwelling bacterium. The organism has yet to be cultured in the laboratory, and very little is known about its physiology. The presence of intracellular inclusions of calcite and sulfur have given rise to speculation that the bacterium is involved in the carbon and sulfur cycles in the sediments where it is found. Depth profiles of oxygen concentration and A. oxaliferum cell numbers in a freshwater sediment revealed that the A. oxaliferum population spanned the oxic-anoxic boundary in the top 3 to 4 cm of sediments. Some of the A. oxaliferum cells resided at depths where no oxygen was detectable, suggesting that these cells may be capable of anaerobic metabolism. The distributions of solid-phase and dissolved inorganic sulfur species in the sediment revealed that A. oxaliferum was most abundant where sulfur cycling was most intense. The sediment was characterized by low concentrations of free sulfide. However, a comparison of sulfate reduction rates in sediment cores incubated with either oxic or anoxic overlying water indicated that the oxidative and reductive components of the sulfur cycle were tightly coupled in the A. oxaliferum-bearing sediment. A positive correlation between pore water sulfate concentration and A. oxaliferum numbers was observed in field data collected over an 18-month period, suggesting a possible link between A. oxaliferum numbers and the oxidation of reduced sulfur species to sulfate. The field data were supported by laboratory incubation experiments in which sodium molybdate-treated sediment cores were augmented with highly purified suspensions of A. oxaliferum cells. Under oxic conditions, rates of sulfate production in the presence of sodium molybdate were found to correlate strongly with the number of cells added to sediment cores, providing further evidence for a role for A. oxaliferum in the oxidation of reduced sulfur.
The chemolithoautotrophic strain Beggiatoa sp. 35Flor shows an unusual migration behavior when cultivated in a gradient medium under high sulfide fluxes. As common for Beggiatoa spp., the filaments form a mat at the oxygen–sulfide interface. However, upon prolonged incubation, a subpopulation migrates actively downward into the anoxic and sulfidic section of the medium, where the filaments become gradually depleted in their sulfur and polyhydroxyalkanoates (PHA) inclusions. This depletion is correlated with the production of hydrogen sulfide. The sulfur- and PHA-depleted filaments return to the oxygen–sulfide interface, where they switch back to depositing sulfur and PHA by aerobic sulfide oxidation. Based on these observations we conclude that internally stored elemental sulfur is respired at the expense of stored PHA under anoxic conditions. Until now, nitrate has always been assumed to be the alternative electron acceptor in chemolithoautotrophic Beggiatoa spp. under anoxic conditions. As the medium and the filaments were free of oxidized nitrogen compounds we can exclude this metabolism. Furthermore, sulfur respiration with PHA under anoxic conditions has so far only been described for heterotrophic Beggiatoa spp., but our medium did not contain accessible organic carbon. Hence the PHA inclusions must originate from atmospheric CO2 fixed by the filaments while at the oxygen–sulfide interface. We propose that the directed migration of filaments into the anoxic section of an oxygen–sulfide gradient system is used as a last resort to preserve cell integrity, which would otherwise be compromised by excessive sulfur deposition occurring in the presence of oxygen and high sulfide fluxes. The regulating mechanism of this migration is still unknown.
Beggiatoa; sulfur reduction; gradient cultivation; microelectrodes; migration
The concentrations of the volatile organic sulfur compounds methanethiol, dimethyl disulfide, and dimethyl sulfide (DMS) and the viable population capable of DMS utilization in laminated microbial ecosystems were evaluated. Significant levels of DMS and dimethyl disulfide (maximum concentrations of 220 and 24 nmol cm3 of sediment-1, respectively) could be detected only at the top 20 mm of the microbial mat, whereas methanethiol was found only at depth horizons from 20 to 50 mm (maximum concentration of 42 nmol cm3 of sediment-1). DMS concentrations in the surface layer doubled after cold hydrolysis of its precursor, dimethylsulfoniopropionate. Most-probable-number counts revealed 2.2 x 10(5) cells cm3 of sediment-1, in the 0- to 5-mm depth horizon, capable of growth on DMS as the sole source of energy. An obligately chemolithoautotrophic bacillus designated strain T5 was isolated from the top layer of the marine sediment. Continuous culture studies in which DMS was the growth-limiting substrate revealed a maximum specific growth rate of 0.10 h-1 and a saturation constant of 90 mumol liter-1 for aerobic growth on this substrate.
Vegetation controls aspects of climate at all scales. These controls operate through fluxes of mass (water vapour, particulates, trace gases, condensation nuclei, and ice nuclei) and energy (latent and sensible heat, radiative exchanges, and momentum dissipation) between the biosphere and the atmosphere. The role these fluxes play in controlling minimum and maximum temperature, temperature range, rainfall, and precipitation processes are detailed. On the hemispheric scale, the importance of evapotranspiration, vegetation surface roughness, and vegetation albedo in the current generation of atmospheric general circulation models is reviewed. Finally, I assess at the planetary scale the global climate effects of biogenic emissions that are well mixed throughout the troposphere. I show that daily maximum and minimum temperatures are, in part, controlled by the emission of non-methane hydrocarbons and transpired water vapour. In many regions, a substantial fraction of the rainfall arises from upstream evapotranspiration rather than from oceanic evaporation. Biosphere evapotranspiration, surface roughness, and albedo are key controls in the general circulation of the atmosphere: climate models that lack adequate specifications for these biosphere attributes fail. The biosphere modulates climate at all scales.
The motility of the purple sulfur bacterium Marichromatium gracile was investigated under different light regimes in a gradient capillary setup with opposing oxygen and sulfide gradients. The gradients were quantified with microsensors, while the behavior of swimming cells was studied by video microscopy in combination with a computerized cell tracking system. M. gracile exhibited photokinesis, photophobic responses, and phobic responses toward oxygen and sulfide. The observed migration patterns could be explained solely by the various phobic responses. In the dark, M. gracile formed an ∼500-μm-thick band at the oxic-anoxic interface, with a sharp border toward the oxic zone always positioned at ∼10 μM O2. Flux calculations yielded a molar conversion ratio Stot/O2 of 2.03:1 (Stot = [H2S] + [HS−] + [S2−]) for the sulfide oxidation within the band, indicating that in darkness the bacteria oxidized sulfide incompletely to sulfur stored in intracellular sulfur globules. In the light, M. gracile spread into the anoxic zone while still avoiding regions with >10 μM O2. The cells also preferred low sulfide concentrations if the oxygen was replaced by nitrogen. A light-dark transition experiment demonstrated a dynamic interaction between the chemical gradients and the cell's metabolism. In darkness and anoxia, M. gracile lost its motility after ca. 1 h. In contrast, at oxygen concentrations of >100 μM with no sulfide present the cells remained viable and motile for ca. 3 days both in light and darkness. Oxygen was respired also in the light, but respiration rates were lower than in the dark. Observed aggregation patterns are interpreted as effective protection strategies against high oxygen concentrations and might represent first stages of biofilm formation.
Main sequence M stars pose an interesting problem for astrobiology: their abundance in our galaxy makes them likely targets in the hunt for habitable planets, but their strong chromospheric activity produces high-energy radiation and charged particles that may be detrimental to life. We studied the impact of the 1985 April 12 flare from the M dwarf AD Leonis (AD Leo), simulating the effects from both UV radiation and protons on the atmospheric chemistry of a hypothetical, Earth-like planet located within its habitable zone. Based on observations of solar proton events and the Neupert effect, we estimated a proton flux associated with the flare of 5.9 × 108 protons cm−2 sr−1 s−1 for particles with energies >10 MeV. Then we calculated the abundance of nitrogen oxides produced by the flare by scaling the production of these compounds during a large solar proton event called the Carrington event. The simulations were performed with a 1-D photochemical model coupled to a 1-D radiative/convective model. Our results indicate that the UV radiation emitted during the flare does not produce a significant change in the ozone column depth of the planet. When the action of protons is included, the ozone depletion reaches a maximum of 94% two years after the flare for a planet with no magnetic field. At the peak of the flare, the calculated UV fluxes that reach the surface, in the wavelength ranges that are damaging for life, exceed those received on Earth during less than 100 s. Therefore, flares may not present a direct hazard for life on the surface of an orbiting habitable planet. Given that AD Leo is one of the most magnetically active M dwarfs known, this conclusion should apply to planets around other M dwarfs with lower levels of chromospheric activity. Key Words: M dwarf—Flare—Habitable zone—Planetary atmospheres. Astrobiology 10, 751–771.
The Black Sea is the largest extant anoxic water body on Earth. Its oxic-anoxic boundary is located at a depth of 100 m and is populated by a single phylotype of marine green sulfur bacteria. This organism, Chlorobium sp. strain BS-1, is extraordinarily low light adapted and can therefore serve as an indicator of deep photic zone anoxia (A. K. Manske, J. Glaeser, M. M. M. Kuypers, and J. Overmann, Appl. Environ. Microbiol. 71:8049-8060, 2005). In the present study, two sediment cores were retrieved from the bottom of the Black Sea at depths of 2,006 and 2,162 m and were analyzed for the presence of subfossil DNA sequences of BS-1 using ancient-DNA methodology. Using optimized cultivation media, viable cells of the BS-1 phylotype were detected only at the sediment surface and not in deeper layers. In contrast, green sulfur bacterial 16S rRNA gene fragments were amplified from all the sediment layers investigated, including turbidites. After separation by denaturing gradient gel electrophoresis and sequencing, 14 different sequence types were distinguished. The sequence of BS-1 represented only a minor fraction of the amplification products and was found in 6 of 22 and 4 of 26 samples from the 2,006- and 2,162-m stations, respectively. Besides the sequences of BS-1, three additional phylotypes of the marine clade of green sulfur bacteria were detected. However, the majority of sequences clustered with groups from freshwater habitats. Our results suggest that a considerable fraction of green sulfur bacterial chemofossils did not originate in a low-light marine chemocline environment and therefore were likely to have an allochthonous origin. Thus, analysis of subfossil DNA sequences permits a more differentiated interpretation and reconstruction of past environmental conditions if specific chemofossils of stenoec species, like Chlorobium sp. strain BS-1, are employed.
Transient-state experiments with the obligately autotrophic Thiobacillus sp. strain W5 revealed that sulfide oxidation proceeds in two physiological phases, (i) the sulfate-producing phase and (ii) the sulfur- and sulfate-producing phase, after which sulfide toxicity occurs. Specific sulfur-producing characteristics were independent of the growth rate. Sulfur formation was shown to occur when the maximum oxidative capacity of the culture was approached. In order to be able to oxidize increasing amounts of sulfide, the organism has to convert part of the sulfide to sulfur (HS(sup-)(symbl)S(sup0) + H(sup+) + 2e(sup-)) instead of sulfate (HS(sup-) + 4H(inf2)O(symbl)SO(inf4)(sup2-) + 9 H(sup+) + 8e(sup-)), thereby keeping the electron flux constant. Measurements of the in vivo degree of reduction of the cytochrome pool as a function of increasing sulfide supply suggested a redox-related down-regulation of the sulfur oxidation rate. Comparison of the sulfur-producing properties of Thiobacillus sp. strain W5 and Thiobacillus neapolitanus showed that the former has twice the maximum specific sulfide-oxidizing capacity of the latter (3.6 versus 1.9 (mu)mol/mg of protein/min). Their maximum specific oxygen uptake rates were very similar. Significant mechanistic differences in sulfur production between the high-sulfur-producing Thiobacillus sp. strain W5 and the moderate-sulfur-producing species T. neapolitanus were not observed. The limited sulfide-oxidizing capacity of T. neapolitanus appears to be the reason that it can convert only 50% of the incoming sulfide to elemental sulfur.
The role of emissions of volatile organic compounds and nitric oxide from biogenic sources is becoming increasingly important in regulatory air quality modeling as levels of anthropogenic emissions continue to decrease and stricter health-based air quality standards are being adopted. However, considerable uncertainties still exist in the current estimation methodologies for biogenic emissions. The impact of these uncertainties on ozone and fine particulate matter (PM2.5) levels for the eastern United States was studied, focusing on biogenic emissions estimates from two commonly used biogenic emission models, the Model of Emissions of Gases and Aerosols from Nature (MEGAN) and the Biogenic Emissions Inventory System (BEIS). Photochemical grid modeling simulations were performed for two scenarios: one reflecting present day conditions and the other reflecting a hypothetical future year with reductions in emissions of anthropogenic oxides of nitrogen (NOx). For ozone, the use of MEGAN emissions resulted in a higher ozone response to hypothetical anthropogenic NOx emission reductions compared with BEIS. Applying the current U.S. Environmental Protection Agency guidance on regulatory air quality modeling in conjunction with typical maximum ozone concentrations, the differences in estimated future year ozone design values (DVF) stemming from differences in biogenic emissions estimates were on the order of 4 parts per billion (ppb), corresponding to approximately 5% of the daily maximum 8-hr ozone National Ambient Air Quality Standard (NAAQS) of 75 ppb. For PM2.5, the differences were 0.1–0.25 μg/m3 in the summer total organic mass component of DVFs, corresponding to approximately 1–2% of the value of the annual PM2.5 NAAQS of 15 μg/m3. Spatial variations in the ozone and PM2.5 differences also reveal that the impacts of different biogenic emission estimates on ozone and PM2.5 levels are dependent on ambient levels of anthropogenic emissions.
Autotrophic denitrification was measured in the southwestern coastal Black Sea, where the Bosporus Plume injects oxidized chemical species (especially O2 and NO3−) into the oxic, suboxic, and anoxic layers. Prominent oxygen intrusions caused an overlap of NOx− and sulfide at the same station where autotrophic denitrification activity was detected with incubation experiments. Several bacteria that have been proposed to oxidize sulfide in other low oxygen environments were found in the Black Sea including SUP05, Sulfurimonas, Arcobacter, and BS-GSO2. Comparison of TRFLP profiles from this mixing zone station and the Western Gyre (a station not affected by the Bosporus Plume) indicate the greatest relative abundance of Sulfurimonas and Arcobacter at the appropriate depths at the mixing zone station. The autotrophic gammaproteobacterium BS-GSO2 correlated with ammonium fluxes rather than with sulfide fluxes and the maximum in SUP05 peak height was shallower than the depths where autotrophic denitrification was detected. Notably, anammox activity was not detected at the mixing zone station, though low levels of DNA from the anammox bacteria Candidatus
Scalindua were present. These results provide evidence for a modified ecosystem with different N2 production pathways in the southwest coastal region compared to that found in the rest of the Black Sea. Moreover, the same Sulfurimonas phylotype (BS139) was previously detected on >30 μm particles in the suboxic zone of the Western Gyre along with DNA of potential sulfate reducers, so it is possible that particle-attached autotrophic denitrification may be an overlooked N2 production pathway in the central Black Sea as well.
Black Sea; autotrophic denitrification; Sulfurimonas; Bosporus Plume; anammox
Dissimilatory sulfate-reducing prokaryotes (SRB) are a very diverse group of anaerobic bacteria that are omnipresent in nature and play an imperative role in the global cycling of carbon and sulfur. In anoxic marine sediments sulfate reduction accounts for up to 50% of the entire organic mineralization in coastal and shelf ecosystems where sulfate diffuses several meters deep into the sediment. As a consequence, SRB would be expected in the sulfate-containing upper sediment layers, whereas methanogenic archaea would be expected to succeed in the deeper sulfate-depleted layers of the sediment. Where sediments are high in organic matter, sulfate is depleted at shallow sediment depths, and biogenic methane production will occur. In the absence of sulfate, many SRB ferment organic acids and alcohols, producing hydrogen, acetate, and carbon dioxide, and may even rely on hydrogen- and acetate-scavenging methanogens to convert organic compounds to methane. SRB can establish two different life styles, and these can be termed as sulfidogenic and acetogenic, hydrogenogenic metabolism. The advantage of having different metabolic capabilities is that it raises the chance of survival in environments when electron acceptors become depleted. In marine sediments, SRB and methanogens do not compete but rather complement each other in the degradation of organic matter. Also in freshwater ecosystems with sulfate concentrations of only 10–200 μM, sulfate is consumed efficiently within the top several cm of the sediments. Here, many of the δ-Proteobacteria present have the genetic machinery to perform dissimilatory sulfate reduction, yet they have an acetogenic, hydrogenogenic way of life. In this review we evaluate the physiology and metabolic mode of SRB in relation with their environment.
sulfate-reducing bacteria; metabolic flexibility; syntrophy; metabolic interactions
Male pattern baldness (MPB), an observable trait, has been reported to be associated with various diseases, such as prostate cancer and cardiovascular disease. Oral sulfur-containing gases have also been suggested to be useful as markers of systemic health condition. However, there are no known reports regarding the associations among MPB, and oral sulfur-containing gases, and systemic health conditions in males.
We studied 170 male subjects aged either 60 or 65 years old. The degree of MPB was assessed using the Norwood-Hamilton Baldness scale. Oral sulfur-containing gases were measured using a compact-designed device. All subjects completed physical and laboratory blood examinations, a face-to-face medical questionnaire, and an oral examination.
There were significant differences between the levels of CH3SCH3 and baldness patterns, independent of age. When we analyzed whether the association was linked to systemic health condition, a strong significant association was observed between the level of CH3SCH3 and severe MPB in subjects with gastrointestinal diseases, hypertension, and hypercholesterolemia.
These results suggest that MPB is associated with the level of CH3SCH3, a sulfur-containing gas that causes oral malodor, in elderly Japanese males. Further, the association was intensified by the existence of gastrointestinal tract and metabolic disorders.
Atmospheric pollution is one of the worst threats to modern society. The consequences derived from different forms of atmospheric pollution vary from the local to the global scale, with deep impacts on climate, environment and human health. Several gaseous pollutants, even when present in trace concentrations, play a fundamental role in important processes that occur in atmosphere. Phenomena such as global warming, photochemical smog formation, acid rain and the depletion of the stratospheric ozone layer are strongly related to the increased concentration of certain gaseous species in the atmosphere. The transport sector significantly produces atmospheric pollution, mainly when diesel oil is used as fuel. Therefore, new methodologies based on selective and sensitive gas detection schemes must be developed in order to detect and monitor pollutant gases from this source. In this work, CO2 Laser Photoacoustic Spectroscopy was used to evaluate ethylene emissions and electrochemical analyzers were used to evaluate the emissions of CO, NOx and SO2 from the exhaust of diesel powered vehicles (rural diesel with 5% of biodiesel, in this paper called only diesel) at different engine rotation speeds. Concentrations in the range 6 to 45 ppmV for ethylene, 109 to 1,231 ppmV for carbon monoxide, 75 to 868 ppmV for nitrogen oxides and 3 to 354 ppmV for sulfur dioxide were obtained. The results indicate that the detection techniques used were sufficiently selective and sensitive to detect the gaseous species mentioned above in the ppmV range.
diesel engines; electrochemical sensors; photoacoustic sensors
CO, one of the most important trace gases, regulates tropospheric methane, hydroxyl radical, and ozone contents. Ten to 25% of the estimated global CO flux may be consumed by soils annually. Depth profiles for 14CO oxidation and CO concentration indicated that CO oxidation occurred primarily in surface soils and that photooxidation of soil organic matter did not necessarily contribute significantly to CO fluxes. Kinetic analyses revealed that the apparent Km was about 18 nM (17 ppm) and the Vmax was 6.9 μmol g (fresh weight)−1 h−1; the apparent Km was similar to the apparent Km for atmospheric methane consumption, but the Vmax was more than 100 times higher. Atmospheric CO oxidation responded sensitively to soil water regimes; decreases in water content in initially saturated soils resulted in increased uptake, and optimum uptake occurred at water contents of 30 to 60%. However, extended drying led to decreased uptake and net CO production. Rewetting could restore CO uptake, albeit with a pronounced hysteresis. The responses to changing temperatures indicated that the optimum temperature for net uptake was between 20 and 25°C and that there was a transition to net production at temperatures above 30°C. The responses to methyl fluoride and acetylene indicated that populations other than ammonia oxidizers and methanotrophs must be involved in forest soils. The response to acetylene was notable, since the strong initial inhibition was reversed after 12 h of incubation; in contrast, methyl fluoride did not have an inhibitory effect. Ammonium did not inhibit CO uptake; the level of nitrite inhibition was initially substantial, but nitrite inhibition was reversible over time. Nitrite inhibition appeared to occur through indirect effects based on abiological formation of NO.
The metabolism of sulfide, sulfur, and acetate by Beggiatoa alba was investigated under oxic and anoxic conditions. B. alba oxidized acetate to carbon dioxide with the stoichiometric reduction of oxygen to water. In vivo acetate oxidation was suppressed by sulfide and by several classic respiratory inhibitors, including dibromothymoquinone, an inhibitor specific for ubiquinones. B. alba also carried out an oxygen-dependent conversion of sulfide to sulfur, a reaction that was inhibited by several electron transport inhibitors but not by dibromothymoquinone, indicating that the electrons released from sulfide oxidation were shuttled to oxygen without the involvement of ubiquinones. Intracellular sulfur stored by B. alba was not oxidized to sulfate or converted to an external soluble form under aerobic conditions. On the other hand, sulfur stored by filaments of Thiothrix nivea was oxidized to extracellular soluble oxidation products, including sulfate. Sulfur stored by filaments of B. alba, however, was reduced to sulfide under short-term anoxic conditions. This anaerobic reduction of sulfur was linked to the endogenous oxidation of stored carbon and to hydrogen oxidation.
Reduction of elemental sulfur was studied in the presence and absencè of thermophilic sulfur-reducing bacteria, at temperatures ranging from 65 to 110°C, in anoxic artificial seawater media. Above 80°C, significant amounts of sulfide were produced abiologically at linear rates, presumably by the disproportionation of sulfur. These rates increased with increasing temperature and pH and were enhanced by yeast extract. In the same medium, the sulfur respiration of two recent thermophilic isolates, a eubacterium and an archaebacterium, resulted in sulfide production at exponential rates. Although not essential for growth, sulfur increased the cell yield in both strains up to fourfold. It is suggested that sulfur respiration is favored at high temperatures and that this process is not limited to archaebacteria, but is shared by other extreme thermophiles.
Reduced sulfur compounds are considered to be important odorants from pig production due to their low odor threshold values and low solubility in slurry. The objective of the present study was to investigate the use of a portable method with a single silica gel column for trapping/separation coupled with chemiluminescence detection (SCTS-CL) for measurement of methanethiol and dimethyl sulfide in sample air from pig production. Proton-transfer-reaction mass spectrometry (PTR-MS) was used to evaluate the trapping/separation. The silica gel column used for the SCTS-CL efficiently collected hydrogen sulfide, methanethiol and dimethyl sulfide. The measurement of methanethiol by SCTS-CL was clearly interfered by the high concentration of hydrogen sulfide found in pig production, and a removal of hydrogen sulfide was necessary to obtain reliable results. Air samples taken from a facility with growing-finishing pigs were analyzed by SCTS-CL, PTR-MS, and a gas chromatograph with sulfur chemiluminescence detection (GC-SCD) to evaluate the SCTS-CL. The difference between the concentrations of methanethiol and dimethyl sulfide measured with SCTS-CL, PTR-MS, and GC-SCD was below 10%. In conclusion, the SCTS-CL is a portable and low-cost alternative to the commercial methods that can be used to measure methanethiol and dimethyl sulfide in sample air from pig production.
Dimethylsulfoniopropionate (DMSP), an osmolyte in marine plants, is biodegraded by cleavage of dimethyl sulfide (DMS) or by demethylation to 3-methiolpropionate (MMPA) and 3-mercaptopropionate (MPA). Sequential demethylation has been observed only with anoxic slurries of coastal sediments. Bacteria that grew aerobically on MMPA and DMSP were isolated from marine environments and phytoplankton cultures. Enrichments with DMSP selected for bacteria that generated DMS, whereas MMPA enrichments selected organisms that produced methanethiol (CH3SH) from either DMSP or MMPA. A bacterium isolated on MMPA grew on MMPA and DMSP, but rapid production of CH3SH from DMSP occurred only with DMSP-grown cells. Low levels of MPA accumulated during growth on MMPA, indicating demethylation as well as demethiolation of MMPA. The alternative routes for DMSP biodegradation via MMPA probably impact on net DMS fluxes to the marine atmosphere.
Members of a group of marine bacteria that is numerically important in coastal seawater and sediments were characterized with respect to their ability to transform organic and inorganic sulfur compounds. Fifteen strains representing the Roseobacter group (a phylogenetic cluster of marine bacteria in the α-subclass of the class Proteobacteria) were isolated from seawater, primarily from the southeastern United States. Although more than one-half of the isolates were obtained without any selection for sulfur metabolism, all of the isolates were able to degrade the sulfur-containing osmolyte dimethyl sulfoniopropionate (DMSP) with production of dimethyl sulfide (DMS). Five isolates also degraded DMSP with production of methanethiol, indicating that both cleavage and demethylation pathways for DMSP occurred in the same organism, which is unusual. Five isolates were able to reduce dimethyl sulfoxide to DMS, and several isolates also degraded DMS and methanethiol. Sulfite oxygenase activity and methanesulfonic acid oxygenase activity were also present in some of the isolates. The ability to incorporate the reduced sulfur in DMSP and methanethiol into cellular material was studied with one of the isolates. A group-specific 16S rRNA probe indicated that the relative abundance of uncultured bacteria in the Roseobacter group increased in seawater enriched with DMSP or DMS. Because this group typically accounts for >10% of the 16S ribosomal DNA pool in coastal seawater and sediments of the southern United States, clues about its potential biogeochemical role are of particular interest. Studies of culturable representatives suggested that the group could mediate a number of steps in the cycling of both organic and inorganic forms of sulfur in marine environments.
Methyl fluoride (CH3F) and dimethyl ether (DME) inhibited nitrification in washed-cell suspensions of Nitrosomonas europaea and in a variety of oxygenated soils and sediments. Headspace additions of CH3F (10% [vol/vol]) and DME (25% [vol/vol]) fully inhibited NO2- and N2O production from NH4+ in incubations of N. europaea, while lower concentrations of these gases resulted in partial inhibition. Oxidation of hydroxylamine (NH2OH) by N. europaea and oxidation of NO2- by a Nitrobacter sp. were unaffected by CH3F or DME. In nitrifying soils, CH3F and DME inhibited N2O production. In field experiments with surface flux chambers and intact cores, CH3F reduced the release of N2O from soils to the atmosphere by 20- to 30-fold. Inhibition by CH3F also resulted in decreased NO3- + NO2- levels and increased NH4+ levels in soils. CH3F did not affect patterns of dissimilatory nitrate reduction to ammonia in cell suspensions of a nitrate-respiring bacterium, nor did it affect N2O metabolism in denitrifying soils. CH3F and DME will be useful in discriminating N2O production via nitrification and denitrification when both processes occur and in decoupling these processes by blocking NO2- and NO3- production.
Strain SY1, identified as a Corynebacterium sp., was isolated on the basis of the ability to utilize dibenzothiophene (DBT) as a sole source of sulfur. Strain SY1 could utilize a wide range of organic and inorganic sulfur compounds, such as DBT sulfone, dimethyl sulfide, dimethyl sulfoxide, dimethyl sulfone, CS2, FeS2, and even elemental sulfur. Strain SY1 metabolized DBT to dibenzothiophene-5-oxide, DBT sulfone, and 2-hydroxybiphenyl, which was subsequently nitrated to produce at least two different hydroxynitrobiphenyls during cultivation. These metabolites were separated by silica gel column chromatography and identified by nuclear magnetic resonance, UV, and mass spectral techniques. Resting cells of SY1 desulfurized toluenesulfonic acid and released sulfite anion. On the basis of these results, a new DBT degradation pathway is proposed.
Polysulfides formed through the breakdown of elemental sulfur or other sulfur compounds were found to be reduced to H2S by the hyperthermophilic archaebacterium Pyrococcus furiosus during growth. Metabolism of polysulfides by the organism was dissimilatory, as no incorporation of 35S-labeled elemental sulfur was detected. However, [35S]cysteine and [35S]methionine were incorporated into cellular protein. Contact between the organism and elemental sulfur is not necessary for metabolism. The sulfide generated from metabolic reduction of polysulfides dissociates to a strong nucleophile, HS−, which in turn opens up the S8 elemental sulfur ring. In addition to H2S, P. furiosus cultures produced methyl mercaptan in a growth-associated fashion.