Search for polythionates in cultures of Chromatium vinosum after sulfide incubation

Cultures of Chromatium vinosum, devoid of sulfur globules, were supplemented with sulfide and incubated under anoxic conditions in the light. The concentrations of sulfide, polysulfides, thiosulfate, polythionates and elemental sulfur (sulfur rings) were monitored for 3 days by ion-chromatography and reversed-phase HPLC. While sulfide disappeared rapidly, thiosulfate and elemental sulfur (S₆, S₇ S₈ rings) were formed. After sulfide depletion, the concentration of thiosulfate decreased fairly rapidly, but elemental sulfur was oxidized very slowly to sulfate. Neither polysulfides (S _x ^2– ), polythionates (S_nO ₆ ^2– , n=4–6), nor other polysulfur compounds could be detected, which is in accordance with the fact that sulfide-grown cells were able to oxidize polysulfide without lag. The nature of the intracellular sulfur globules is discussed.     

Succession of Internal Sulfur Cycles and Sulfur-Oxidizing Bacterial Communities in Microaerophilic Wastewater Biofilms

The succession of sulfur-oxidizing bacterial (SOB) community structure and the complex internal sulfur cycle occurring in wastewater biofilms growing under microaerophilic conditions was analyzed by using a polyphasic approach that employed 16S rRNA gene-cloning analysis combined with fluorescence in situ hybridization, microelectrode measurements, and standard batch and reactor experiments. A complete sulfur cycle was established via S⁰ accumulation within 80 days in the biofilms in replicate. This development was generally split into two phases, (i) a sulfur-accumulating phase and (ii) a sulfate-producing phase. In the first phase (until about 40 days), since the sulfide production rate (sulfate-reducing activity) exceeded the maximum sulfide-oxidizing capacity of SOB in the biofilms, H₂S was only partially oxidized to S⁰ by mainly Thiomicrospira denitirificans with NO₃⁻ as an electron acceptor, leading to significant accumulation of S⁰ in the biofilms. In the second phase, the SOB populations developed further and diversified with time. In particular, S⁰ accumulation promoted the growth of a novel strain, strain SO07, which predominantly carried out the oxidation of S⁰ to SO₄²⁻ under oxic conditions, and Thiothrix sp. strain CT3. In situ hybridization analysis revealed that the dense populations of Thiothrix (ca. 10⁹ cells cm⁻³) and strain SO07 (ca. 10⁸ cells cm⁻³) were found at the sulfur-rich surface (100 μm), while the population of Thiomicrospira denitirificans was distributed throughout the biofilms with a density of ca. 10⁷ to 10⁸ cells cm⁻³. Microelectrode measurements revealed that active sulfide-oxidizing zones overlapped the spatial distributions of different phylogenetic SOB groups in the biofilms. As a consequence, the sulfide-oxidizing capacities of the biofilms became high enough to completely oxidize all H₂S produced by SRB to SO₄²⁻ in the second phase, indicating establishment of the complete sulfur cycle in the biofilms.     

Anaerobic Sulfide Oxidation with Nitrate by a Freshwater Beggiatoa Enrichment Culture

A lithotrophic freshwater Beggiatoa strain was enriched in O₂-H₂S gradient tubes to investigate its ability to oxidize sulfide with NO₃⁻ as an alternative electron acceptor. The gradient tubes contained different NO₃⁻ concentrations, and the chemotactic response of the Beggiatoa mats was observed. The effects of the Beggiatoa sp. on vertical gradients of O₂, H₂S, pH, and NO₃⁻ were determined with microsensors. The more NO₃⁻ that was added to the agar, the deeper the Beggiatoa filaments glided into anoxic agar layers, suggesting that the Beggiatoa sp. used NO₃⁻ to oxidize sulfide at depths below the depth that O₂ penetrated. In the presence of NO₃⁻ Beggiatoa formed thick mats (>8 mm), compared to the thin mats (ca. 0.4 mm) that were formed when no NO₃⁻ was added. These thick mats spatially separated O₂ and sulfide but not NO₃⁻ and sulfide, and therefore NO₃⁻ must have served as the electron acceptor for sulfide oxidation. This interpretation is consistent with a fourfold-lower O₂ flux and a twofold-higher sulfide flux into the NO₃⁻-exposed mats compared to the fluxes for controls without NO₃⁻. Additionally, a pronounced pH maximum was observed within the Beggiatoa mat; such a pH maximum is known to occur when sulfide is oxidized to S⁰ with NO₃⁻ as the electron acceptor.     

Characterization of elemental sulfur in isolated intact spinach chloroplasts

Incubation of intact spinach (Spinacia oleracea L.) chloroplasts in the presence of ³⁵SO₄²⁻ resulted in the light-dependent formation of a chloroform-soluble sulfur-containing compound distinct from sulfolipid. We have identified this compound as the most stable form (S₈) of elemental sulfur (S⁰, valence state for S = O) by mass spectrometry. It is possible that elemental sulfur (S⁰) was formed by oxidation of bound sulfide, i.e. after the photoreduction of sulfate to sulfide by intact chloroplasts, and released as S₈ under the experimental conditions used for analysis.     

Nitrogen, Carbon, and Sulfur Metabolism in Natural Thioploca Samples

Filamentous sulfur bacteria of the genus Thioploca occur as dense mats on the continental shelf off the coast of Chile and Peru. Since little is known about their nitrogen, sulfur, and carbon metabolism, this study was undertaken to investigate their (eco)physiology. Thioploca is able to store internally high concentrations of sulfur globules and nitrate. It has been previously hypothesized that these large vacuolated bacteria can oxidize sulfide by reducing their internally stored nitrate. We examined this nitrate reduction by incubation experiments of washed Thioploca sheaths with trichomes in combination with ¹⁵N compounds and mass spectrometry and found that these Thioploca samples produce ammonium at a rate of 1 nmol min⁻¹ mg of protein⁻¹. Controls showed no significant activity. Sulfate was shown to be the end product of sulfide oxidation and was observed at a rate of 2 to 3 nmol min⁻¹ mg of protein⁻¹. The ammonium and sulfate production rates were not influenced by the addition of sulfide, suggesting that sulfide is first oxidized to elemental sulfur, and in a second independent step elemental sulfur is oxidized to sulfate. The average sulfide oxidation rate measured was 5 nmol min⁻¹ mg of protein⁻¹ and could be increased to 10.7 nmol min⁻¹ mg of protein⁻¹ after the trichomes were starved for 45 h. Incorporation of ¹⁴CO₂ was at a rate of 0.4 to 0.8 nmol min⁻¹ mg of protein⁻¹, which is half the rate calculated from sulfide oxidation. [2-¹⁴C]acetate incorporation was 0.4 nmol min⁻¹ mg of protein⁻¹, which is equal to the CO₂ fixation rate, and no ¹⁴CO₂ production was detected. These results suggest that Thioploca species are facultative chemolithoautotrophs capable of mixotrophic growth. Microautoradiography confirmed that Thioploca cells assimilated the majority of the radiocarbon from [2-¹⁴C]acetate, with only a minor contribution by epibiontic bacteria present in the samples.     

Role of Polysulfides in Reduction of Elemental Sulfur by the Hyperthermophilic Archaebacterium Pyrococcus furiosus

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.     

Kinetic Studies of Bacterial Sulfate Reduction in Freshwater Sediments by High-Pressure Liquid Chromatography and Microdistillation

Indirect photometric chromatography and microdistillation enabled a simultaneous measurement of sulfate depletion and sulfide production in the top 3 cm of freshwater sediments to be made. The simultaneous measurement of sulfate depletion and sulfide production rates provided added insight into microbial sulfur metabolism. The lower sulfate reduction rates, as derived from the production of acid-volatile ³⁵S²⁻ only, were explained by a conversion of this pool to an undistillable fraction under acidic conditions during incubation. A mathematical model was applied to calculate sulfate reduction from sulfate gradients at the sediment-water interface. To avoid disturbance of these gradients, the sample volume was reduced to 0.2 g (wet weight) of sediment. Sulfate diffusion coefficients in the model were determined (D_s = 0.3 × 10⁻⁵ cm² s⁻¹ at 6°C). The results of the model were compared with those of radioactive sulfate turnover experiments by assessing the actual turnover rate constants (2 to 5 day⁻¹) and pool sizes of sulfate at different sediment depths.     

Motility of Marichromatium gracile in Response to Light, Oxygen, and Sulfide

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 S_tot/O₂ of 2.03:1 (S_tot = [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.     

Reduction of Sulfur Compounds in the Sediments of a Eutrophic Lake Basin

Concentrations of various sulfur compounds (SO₄²⁻, H₂S, S⁰, acid-volatile sulfide, and total sulfur) were determined in the profundal sediments and overlying water column of a shallow eutrophic lake. Low concentrations of sulfate relative to those of acid-volatile sulfide and total sulfur and a decrease in total sulfur with sediment depth implied that the contribution of dissimilatory sulfur reduction to H₂S production was relatively minor. Addition of 1.0 mM Na₂³⁵SO₄ to upper sediments in laboratory experiments resulted in the production of H₂³⁵S with no apparent lag. Kinetic experiments with ³⁵S demonstrated an apparent K_m of 0.068 mmol of SO₄²⁻ reduced per liter of sediment per day, whereas tracer experiments with ³⁵S indicated an average turnover time of the sediment sulfate pool of 1.5 h. Total sulfate reduction in a sediment depth profile to 15 cm was 15.3 mmol of sulfate reduced per m² per day, which corresponds to a mineralization of 30% of the particulate organic matter entering the sediment. Reduction of ³⁵S⁰ occurred at a slower rate. These results demonstrated that high rates of sulfate reduction occur in these sediments despite low concentrations of oxidized inorganic compounds and that this reduction can be important in the anaerobic mineralization of organic carbon.     

Isolation, Characterization, and In Situ Detection of a Novel Chemolithoautotrophic Sulfur-Oxidizing Bacterium in Wastewater Biofilms Growing under Microaerophilic Conditions

We successfully isolated a novel aerobic chemolithotrophic sulfur-oxidizing bacterium, designated strain SO07, from wastewater biofilms growing under microaerophilic conditions. For isolation, the use of elemental sulfur (S⁰), which is the most abundant sulfur pool in the wastewater biofilms, as the electron donor was an effective measure to establish an enrichment culture of strain SO07 and further isolation. 16S rRNA gene sequence analysis revealed that newly isolated strain SO07 was affiliated with members of the genus Halothiobacillus, but it was only distantly related to previously isolated species (89% identity). Strain SO07 oxidized elemental sulfur, thiosulfate, and sulfide to sulfate under oxic conditions. Strain SO07 could not grow on nitrate. Organic carbons, including acetate, propionate, and formate, could not serve as carbon and energy sources. Unlike other aerobic sulfur-oxidizing bacteria, this bacterium was sensitive to NaCl; growth in medium containing more than 150 mM was negligible. In situ hybridization combined with confocal laser scanning microscopy revealed that a number of rod-shaped cells hybridized with a probe specific for strain SO07 were mainly present in the oxic biofilm strata (ca. 0 to 100 μm) and that they often coexisted with sulfate-reducing bacteria in this zone. These results demonstrated that strain SO07 was one of the important sulfur-oxidizing populations involved in the sulfur cycle occurring in the wastewater biofilm and was primarily responsible for the oxidation of H₂S and S⁰ to SO₄²⁻ under oxic conditions.     

Impact of Bacterial NO3? Transport on Sediment Biogeochemistry

Experiments demonstrated that Beggiatoa could induce a H₂S-depleted suboxic zone of more than 10 mm in marine sediments and cause a divergence in sediment NO₃⁻ reduction from denitrification to dissimilatory NO₃⁻ reduction to ammonium. pH, O₂, and H₂S profiles indicated that the bacteria oxidized H₂S with NO₃⁻ and transported S⁰ to the sediment surface for aerobic oxidation.     

Sulfur disproportionating microbial communities in a dynamic,microoxic-sulfidic karst system

Biogeochemical sulfur cycling in sulfidic karst systems is largely driven by abiotic and biological sulfide oxidation, but the fate of elemental sulfur (S⁰) that accumulates in these systems is not well understood. The Frasassi Cave system (Italy) is intersected by a sulfidic aquifer that mixes with small quantities of oxygen-rich meteoric water, creating Proterozoic-like conditions and supporting a prolific ecosystem driven by sulfur-based chemolithoautotrophy. To better understand the cycling of S⁰ in this environment, we examined the geochemistry and microbiology of sediments underlying widespread sulfide-oxidizing mats dominated by Beggiatoa. Sediment populations were dominated by uncultivated relatives of sulfur cycling chemolithoautotrophs related to Sulfurovum, Halothiobacillus, Thiofaba, Thiovirga, Thiobacillus, and Desulfocapsa, as well as diverse uncultivated anaerobic heterotrophs affiliated with Bacteroidota, Anaerolineaceae, Lentimicrobiaceae, and Prolixibacteraceae. Desulfocapsa and Sulfurovum populations accounted for 12%–26% of sediment 16S rRNA amplicon sequences and were closely related to isolates which carry out autotrophic S⁰ disproportionation in pure culture. Gibbs energy (∆G_r) calculations revealed that S⁰ disproportionation under in situ conditions is energy yielding. Microsensor profiles through the mat-sediment interface showed that Beggiatoa mats consume dissolved sulfide and oxygen, but a net increase in acidity was only observed in the sediments below. Together, these findings suggest that disproportionation is an important sink for S⁰ generated by microbial sulfide oxidation in this oxygen-limited system and may contribute to the weathering of carbonate rocks and sediments in sulfur-rich environments.     

Colorless Sulfur Bacteria, Beggiatoa spp. and Thiovulum spp., in O2 and H2S Microgradients

The interactions between colorless sulfur bacteria and the chemical microgradients at the oxygen-sulfide interface were studied in Beggiatoa mats from marine sediments and in Thiovulum veils developing above the sediments. The gradients of O₂, H₂S, and pH were measured by microelectrodes at depth increments of 50 μm. An unstirred boundary layer in the water surrounding the mats and veils prevented microturbulent or convective mixing of O₂ and H₂S. The two substrates reached the bacteria only by molecular diffusion through the boundary layer. The bacteria lived as microaerophiles or anaerobes even under stirred, oxic water. Oxygen and sulfide zones overlapped by 50 μm in the bacterial layers. Both compounds had concentrations in the range of 0 to 10 μmol liter⁻¹ and residence times of 0.1 to 0.6 s in the overlapping zone. The sulfide oxidation was purely biological. Diffusion calculations showed that formation of mats on solid substrates or of veils in the water represented optimal strategies for the bacteria to achieve a stable microenvironment, a high substrate supply, and an efficient competition with chemical sulfide oxidation. The continuous gliding movement of Beggiatoa cells in mats or the flickering motion of Thiovulum cells in veils were important for the availability of both O₂ and H₂S for the individual bacteria.     

Light-Dependent Sulfide Oxidation in the Anoxic Zone of the Chesapeake Bay Can Be Explained by Small Populations of Phototrophic Bacteria

Microbial sulfide oxidation in aquatic environments is an important ecosystem process, as sulfide is potently toxic to aerobic organisms. Sulfide oxidation in anoxic waters can prevent the efflux of sulfide to aerobic water masses, thus mitigating toxicity. The contribution of phototrophic sulfide-oxidizing bacteria to anaerobic sulfide oxidation in the Chesapeake Bay and the redox chemistry of the stratified water column were investigated in the summers of 2011 to 2014. In 2011 and 2013, phototrophic sulfide-oxidizing bacteria closely related to Prosthecochloris species of the phylum Chlorobi were cultivated from waters sampled at and below the oxic-anoxic interface, where measured light penetration was sufficient to support populations of low-light-adapted photosynthetic bacteria. In 2012, 2013, and 2014, light-dependent sulfide loss was observed in freshly collected water column samples. In these samples, extremely low light levels caused 2- to 10-fold increases in the sulfide uptake rate over the sulfide uptake rate under dark conditions. An enrichment, CB11, dominated by Prosthecochloris species, oxidized sulfide with a K_s value of 11 μM and a V_max value of 51 μM min⁻¹ (mg protein⁻¹). Using these kinetic values with in situ sulfide concentrations and light fluxes, we calculated that a small population of Chlorobi similar to those in enrichment CB11 can account for the observed anaerobic light-dependent sulfide consumption activity in natural water samples. We conclude that Chlorobi play a far larger role in the Chesapeake Bay than currently appreciated. This result has potential implications for coastal anoxic waters and expanding oxygen-minimum zones as they begin to impinge on the photic zone.     

Involvement of Intermediate Sulfur Species in Biological Reduction of Elemental Sulfur under Acidic,Hydrothermal Conditions

The thermoacidophile and obligate elemental sulfur (S₈⁰)-reducing anaerobe Acidilobus sulfurireducens 18D70 does not associate with bulk solid-phase sulfur during S₈⁰-dependent batch culture growth. Cyclic voltammetry indicated the production of hydrogen sulfide (H₂S) as well as polysulfides after 1 day of batch growth of the organism at pH 3.0 and 81°C. The production of polysulfide is likely due to the abiotic reaction between S₈⁰ and the biologically produced H₂S, as evinced by a rapid cessation of polysulfide formation when the growth temperature was decreased, inhibiting the biological production of sulfide. After an additional 5 days of growth, nanoparticulate S₈⁰ was detected in the cultivation medium, a result of the hydrolysis of polysulfides in acidic medium. To examine whether soluble polysulfides and/or nanoparticulate S₈⁰ can serve as terminal electron acceptors (TEA) supporting the growth of A. sulfurireducens, total sulfide concentration and cell density were monitored in batch cultures with S₈⁰ provided as a solid phase in the medium or with S₈⁰ sequestered in dialysis tubing. The rates of sulfide production in 7-day-old cultures with S₈⁰ sequestered in dialysis tubing with pore sizes of 12 to 14 kDa and 6 to 8 kDa were 55% and 22%, respectively, of that of cultures with S₈⁰ provided as a solid phase in the medium. These results indicate that the TEA existed in a range of particle sizes that affected its ability to diffuse through dialysis tubing of different pore sizes. Dynamic light scattering revealed that S₈⁰ particles generated through polysulfide rapidly grew in size, a rate which was influenced by the pH of the medium and the presence of organic carbon. Thus, S₈⁰ particles formed through abiological hydrolysis of polysulfide under acidic conditions appeared to serve as a growth-promoting TEA for A. sulfurireducens.     

Effect of Sulfide on Nitrogen Fixation in a Stream Sediment-Water System

Nitrogen fixation (C₂H₂ reduction) in a sediment-water system was studied under anaerobic incubation conditions. Sodium sulfide at low concentrations stimulated activity, with a twofold increase in C₂H₄ production occurring in the presence of 8 μmol of S²⁻ per ml of stream water. Sodium sulfide at concentrations of 16 μmol of S²⁻ per ml or greater inhibited nitrogen fixation, with 64 μmol of S²⁻ per ml being completely inhibitory. Sulfide at levels of 16 μmol/ml or above inhibited CO₂ production, and the degree of inhibition increased with increasing concentration of sulfide. Titanium (III) citrate (used to modify Eh levels) stimulated both nitrogen fixation and CO₂ production, but could not duplicate, at any concentration tested, the twofold increase in nitrogen fixation caused by 8 μmol of S²⁻ per ml. Sulfide additions caused pH changes in the sediment, and when the sediment was adjusted and maintained at pH 7.0 all concentrations of sulfide inhibited nitrogen fixation activity. From considerations of the redox equilibria of H₂, H₂S, and other sulfur species at various pH values, it appeared that H₂S was the toxic entity and that HS⁻ was less toxic. The observed stimulation of activity was apparently due to a pH change coupled with the concurrent production of HS⁻ from H₂S.     

Inorganic Sulfur Oxidation by Aureobasidium pullulans

Aureobasidium pullulans (de Bary) Arnaud isolated from the phylloplane of sycamore exposed to heavy atmospheric pollution oxidized S⁰ to S₂O₃²⁻, S₄O₆²⁻, and SO₄²⁻ in vitro. The intermediates S₂O₃²⁻ and S₄O₆²⁻ were also oxidized to SO₄²⁻. Cell-free extracts of A. pullulans also oxidized reduced forms of S, the oxidation increasing linearly with increasing protein concentration, showing that the process is enzymatic. The possible role of fungi in S oxidation in soils is discussed.     

Sulfate Reduction in Peat from a New Jersey Pinelands Cedar Swamp

Microbial sulfate reduction rates in acidic peat from a New Jersey Pine Barrens cedar swamp in 1986 were similar to sulfate reduction rates in freshwater lake sediments. The rates ranged from a low of 1.0 nmol cm⁻³ day⁻¹ in February at 7.5- to 10.0-cm depth to 173.4 nmol cm⁻³ day⁻¹ in July at 5.0- to 7.5-cm depth. The presence of living Sphagnum moss at the surface generally resulted in reduced rates of sulfate reduction. Pore water sulfate concentrations and water table height also apparently affected the sulfate reduction rate. Concentrations of sulfate in pore water were nearly always higher than those in surface water and groundwater, ranging from 26 to 522 μM. The elevated pore water sulfate levels did not result from the evapotranspiratory concentration of infiltrating stream water or groundwater, but probably resulted from oxidation of reduced sulfur compounds, hydrolysis of ester sulfates present in the peat, or both. The total sulfur content of peat that had no living moss at the surface was 164.64 ± 1.5 and 195.8 ± 21.7 μmol g (dry weight)⁻¹ for peat collected from 2.5 to 5.0 and 7.5 to 10.0 cm, respectively. Organosulfur compounds accounted for 84 to 88% of the total sulfur that was present in the peat. C-bonded sulfur accounted for 91 to 94% of the organic sulfur, with ester sulfate being only a minor constituent. Reduced inorganic sulfur species in peat from 2.5 to 7.5 cm were dominated by H₂S-FeS (68%), while pyritic sulfide was the predominant inorganic sulfur species in the peat from depths of 7.5 to 10.0 cm (75%).     

Growth kinetics of haloalkaliphilic,sulfur-oxidizing bacterium<Emphasis Type="Italic"> Thioalkalivibrio versutus</Emphasis> strain ALJ 15 in continuous culture

The chemolithoautotrophic, sulfur-oxidizing bacterium Thioalkalivibrio versutus strain ALJ 15, isolated from a soda lake in Kenya, was grown in a continuous culture, with thiosulfate or polysulfide as growth-limiting energy source and oxygen as electron acceptor, at pH 10 and at pH 0.6, 2 M and 4 M total sodium. The end product of the sulfur-compound oxidation was sulfate. Elemental sulfur and a cell-bound, polysulfide-like compound appeared as intermediates during substrate oxidation. In the thiosulfate-limited culture, the biomass yields and maximum specific growth rates decreased two and three times, respectively, with increasing sodium concentration. The apparent affinity constant measured for thiosulfate and polysulfide was in the micromolar range (K_s=6±3 M). The maintenance requirement (m_s=8±5 mmol S₂O₃²/g dry weight h^–1) was in the range of values found for other autotrophic sulfur-oxidizing bacteria. The organism had a comparable maximum specific rate of oxygen uptake with thiosulfate, polysulfide, and sulfide, while elemental sulfur was oxidized at a lower rate. Glycine betaine was the main organic compatible solute. The respiration rates with different species of polysulfides (S_n^2–) were tested. All polysulfide species were completely oxidized at high rates to sulfate. Overall data demonstrated efficient growth and sulfur compounds oxidation of haloalkaliphilic chemolithoautotrophic bacteria from soda lakes.Communicated by W.D. Grant