Intracellular Sulfur Globules Research Articles

Synergistic phenotypic adaptations of motile purple sulphur bacteria Chromatium okenii during lake-to-laboratory domestication.

Isolating microorganisms from natural environments for cultivation under optimized laboratory settings has markedly improved our understanding of microbial ecology. Artificial growth conditions often diverge from those in natural ecosystems, forcing wild isolates into distinct selective pressures, resulting in diverse eco-physiological adaptations mediated by modification of key phenotypic traits. For motile microorganisms we still lack a biophysical understanding of the relevant traits emerging during domestication and their mechanistic interplay driving short-to-long-term microbial adaptation under laboratory conditions. Using microfluidics, atomic force microscopy, quantitative imaging, and mathematical modeling, we study phenotypic adaptation of Chromatium okenii, a motile phototrophic purple sulfur bacterium from meromictic Lake Cadagno, grown under laboratory conditions over multiple generations. Our results indicate that naturally planktonic C. okenii leverage shifts in cell-surface adhesive interactions, synergistically with changes in cell morphology, mass density, and distribution of intracellular sulfur globules, to suppress their swimming traits, ultimately switching to a sessile lifeform. A computational model of cell mechanics confirms the role of such phenotypic shifts in suppressing the planktonic lifeform. By investigating key phenotypic traits across different physiological stages of lab-grown C. okenii, we uncover a progressive loss of motility during the early stages of domestication, followed by concomitant deflagellation and enhanced surface attachment, ultimately driving the transition of motile sulfur bacteria to a sessile state. Our results establish a mechanistic link between suppression of motility and surface attachment via phenotypic changes, underscoring the emergence of adaptive fitness under laboratory conditions at the expense of traits tailored for natural environments.

Insight into the metabolic potential and ecological function of a novel Magnetotactic Nitrospirota in coral reef habitat.

Magnetotactic bacteria (MTB) within the Nitrospirota phylum play important roles in biogeochemical cycles due to their outstanding ability to biomineralize large amounts of magnetite magnetosomes and intracellular sulfur globules. For several decades, Nitrospirota MTB were believed to only live in freshwater or low-salinity environments. While this group have recently been found in marine sediments, their physiological features and ecological roles have remained unclear. In this study, we combine electron microscopy with genomics to characterize a novel population of Nitrospirota MTB in a coral reef area of the South China Sea. Both phylogenetic and genomic analyses revealed it as representative of a novel genus, named as Candidatus Magnetocorallium paracelense XS-1. The cells of XS-1 are small and vibrioid-shaped, and have bundled chains of bullet-shaped magnetite magnetosomes, sulfur globules, and cytoplasmic vacuole-like structures. Genomic analysis revealed that XS-1 has the potential to respire sulfate and nitrate, and utilize the Wood-Ljungdahl pathway for carbon fixation. XS-1 has versatile metabolic traits that make it different from freshwater Nitrospirota MTB, including Pta-ackA pathway, anaerobic sulfite reduction, and thiosulfate disproportionation. XS-1 also encodes both the cbb3-type and the aa3-type cytochrome c oxidases, which may function as respiratory energy-transducing enzymes under high oxygen conditions and anaerobic or microaerophilic conditions, respectively. XS-1 has multiple copies of circadian related genes in response to variability in coral reef habitat. Our results implied that XS-1 has a remarkable plasticity to adapt the environment and can play a beneficial role in coral reef ecosystems.

Large sulfur oxidizing bacteria of the Thiovulaceae (Campylobacterota) thriving in the sulfidic groundwater of Movile Cave, in Romania

Life in Movile Cave (Romania) relies entirely on carbon fixation by bacteria oxidizing sulfide, methane and ammonia, using oxygen, nitrate, sulfate, and ferric iron as electron acceptors. There, our attention was drawn by a white veil-like structure at the water surface. Microscopic analysis of the veil revealed a dense population of microorganisms of various shapes and sizes, some of which being much larger than the other spirilla, rods and cocci that could be observed. We studied these larger microorganisms with optical and electron microscopy techniques, sequenced their genome and analyzed the main physiological abilities. Their shape is spherical to ovoid, 12-16 µm in diameter, and their cytoplasm is rich in intracellular sulfur globules. They are present in densities of up to 5.5×103 cells/ml and they are very motile. These cells were identified as Thiovulum sp. (Campylobacterota), forming a separated cluster from marine Thiovulum sp., consisting mostly of cave bacteria. The Thiovulum microhabitat is located at the water surface in the lower, partially submerged, level of Movile Cave. Here, H2S is brought in by diffusion and convection, and some water flow is only present deep below the water surface. Frequent attachment is observed between cells, which is consistent with other reports of Thiovulum sp. being clustered in dense, veil like, aggregates attached to polysaccharide matrices. Nevertheless, the Movile Cave strain occurs in the water and is not attached to any rocky surface. The Movile Cave Thiovulum genome is small at 1.72 Mbp, contains 1804 coding sequences, 3 rRNA operons, and has a GC content of 28%. The genome suggested that the Movile Cave Thiovulum strain can switch between aerobic and anaerobic sulfide oxidation using O2 and NO3- as electron acceptors, respectively. In the latter case, NO3- is likely reduced by Thiovulum to NH3 via dissimilatory nitrate reduction, thereby contributing to the complete nitrogen cycle in this environment. Additionally, coupling the genomic analysis, with new electron microscopy images, we suggest that in absence of motor-like structures along the membrane, the short peritrichous filamentous structures, typical to Thiovulum, are pili, likely of type IV, for which genes were found in all 6 available Thiovulum genomes. These pili may play a role in veil formation, connecting adjacent cells and support the exceptionally fast swimming behavior of these bacteria.

Sub-micrometer-scale mapping of magnetite crystals and sulfur globules in magnetotactic bacteria using confocal Raman micro-spectrometry.

The ferrimagnetic mineral magnetite is biomineralized by magnetotactic microorganisms and a diverse range of animals. Here we demonstrate that confocal Raman microscopy can be used to visualize chains of magnetite crystals in magnetotactic bacteria, even though magnetite is a poor Raman scatterer and in bacteria occurs in typical grain sizes of only 35–120 nm, well below the diffraction-limited optical resolution. When using long integration times together with low laser power (<0.25 mW) to prevent laser induced damage of magnetite, we can identify and map magnetite by its characteristic Raman spectrum (303, 535, 665 ) against a large autofluorescence background in our natural magnetotactic bacteria samples. While greigite (cubic ; Raman lines of 253 and 351 ) is often found in the Deltaproteobacteria class, it is not present in our samples. In intracellular sulfur globules of Candidatus Magnetobacterium bavaricum (Nitrospirae), we identified the sole presence of cyclo-octasulfur (: 151, 219, 467 ), using green (532 nm), red (638 nm) and near-infrared excitation (785 nm). The Raman-spectra of phosphorous-rich intracellular accumulations point to orthophosphate in magnetic vibrios and to polyphosphate in magnetic cocci. Under green excitation, the cell envelopes are dominated by the resonant Raman lines of the heme cofactor of the b or c-type cytochrome, which can be used as a strong marker for label-free live-cell imaging of bacterial cytoplasmic membranes, as well as an indicator for the redox state.

Regulation of Dissimilatory Sulfur Oxidation in the Purple Sulfur Bacterium Allochromatium Vinosum

In the purple sulfur bacterium Allochromatium vinosum, thiosulfate oxidation is strictly dependent on the presence of three periplasmic Sox proteins encoded by the soxBXAK and soxYZ genes. It is also well documented that proteins encoded in the dissimilatory sulfite reductase (dsr) operon, dsrABEFHCMKLJOPNRS, are essential for the oxidation of sulfur that is stored intracellularly as an obligatory intermediate during the oxidation of thiosulfate and sulfide. Until recently, detailed knowledge about the regulation of the sox genes was not available. We started to fill this gap and show that these genes are expressed on a low constitutive level in A. vinosum in the absence of reduced sulfur compounds. Thiosulfate and possibly sulfide lead to an induction of sox gene transcription. Additional translational regulation was not apparent. Regulation of soxXAK is probably performed by a two-component system consisting of a multi-sensor histidine kinase and a regulator with proposed di-guanylate cyclase activity. Previous work already provided some information about regulation of the dsr genes encoding the second important sulfur-oxidizing enzyme system in the purple sulfur bacterium. The expression of most dsr genes was found to be at a low basal level in the absence of reduced sulfur compounds and enhanced in the presence of sulfide. In the present work, we focused on the role of DsrS, a protein encoded by the last gene of the dsr locus in A. vinosum. Transcriptional and translational gene fusion experiments suggest a participation of DsrS in the post-transcriptional control of the dsr operon. Characterization of an A. vinosum ΔdsrS mutant showed that the monomeric cytoplasmic 41.1-kDa protein DsrS is important though not essential for the oxidation of sulfur stored in the intracellular sulfur globules.

Sulfur Species Investigation in Extra- and Intracellular Sulfur Globules of Acidithiobacillus ferrooxidans and Acidithiobacillus caldus

The sulfur chemical speciation in extracellular and intracellular sulfur globules of Acidithiobacillus ferrooxidans and Acidithiobacillus caldus were investigated with an integrated approach including scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES). The results indicated that both strains can accumulate extracellular sulfur globules when grown on thiosulfate, and the major sulfur chemical speciation of which were S8 for A. ferrooxidans and mixture of ring sulfur and polythionate for A. caldus, respectively. In contrast, A. ferrooxidans can accumulate both linear sulfur and S8 internally when grown with sulfur powder and thiosulfate, whereas A. caldus did not accumulate intracellular sulfur globules. In addition, the fitted results of sulfur K-edge XANES spectra indicated that the reduced glutathione (containing thiols groups) were involved in sulfur bio-oxidation of both strains and the tetrathionate were the intermediate products during thiosulfate metabolism by two strains.

DsrR, a Novel IscA-Like Protein Lacking Iron- and Fe-S-Binding Functions, Involved in the Regulation of Sulfur Oxidation inAllochromatium vinosum

In the purple sulfur bacterium Allochromatium vinosum, the reverse-acting dissimilatory sulfite reductase (DsrAB) is the key enzyme responsible for the oxidation of intracellular sulfur globules. The genes dsrAB are the first and the gene dsrR is the penultimate of the 15 genes of the dsr operon in A. vinosum. Genes homologous to dsrR occur in a number of other environmentally important sulfur-oxidizing bacteria utilizing Dsr proteins. DsrR exhibits sequence similarities to A-type scaffolds, like IscA, that partake in the maturation of protein-bound iron-sulfur clusters. We used nuclear magnetic resonance (NMR) spectroscopy to solve the solution structure of DsrR and to show that the protein is indeed structurally highly similar to A-type scaffolds. However, DsrR does not retain the Fe-S- or the iron-binding ability of these proteins, which is due to the lack of all three highly conserved cysteine residues of IscA-like scaffolds. Taken together, these findings suggest a common function for DsrR and IscA-like proteins different from direct participation in iron-sulfur cluster maturation. An A. vinosum DeltadsrR deletion strain showed a significantly reduced sulfur oxidation rate that was fully restored upon complementation with dsrR in trans. Immunoblot analyses revealed a reduced level of DsrE and DsrL in the DeltadsrR strain. These proteins are absolutely essential for sulfur oxidation. Transcriptional and translational gene fusion experiments suggested the participation of DsrR in the posttranscriptional control of the dsr operon, similar to the alternative function of cyanobacterial IscA as part of the sense and/or response cascade set into action upon iron limitation.

Structural and Molecular Genetic Insight into a Widespread Sulfur Oxidation Pathway

Many environmentally important photo- and chemolithoautotrophic bacteria accumulate globules of polymeric, water-insoluble sulfur as a transient product during oxidation of reduced sulfur compounds. Oxidation of this sulfur requires the concerted action of Dsr proteins. However, individual functions and interplay of these proteins are largely unclear. We proved with a ΔdsrE mutant experiment that the cytoplasmic α2β2γ2-structured protein DsrEFH is absolutely essential for the oxidation of sulfur stored in the intracellular sulfur globules of the purple sulfur bacterial model organism Allochromatium vinosum. The ability to degrade stored sulfur was fully regained upon complementation with dsrEFH in trans. The crystal structure of DsrEFH was determined at 2.5 Å resolution to assist functional assignment in detail. In conjunction with phylogenetic analyses, two different types of putative active sites were identified in DsrE and DsrH and shown to be characteristic for sulfur-oxidizing bacteria. Conserved Cys78 of A. vinosum DsrE corresponds to the active cysteines of Escherichia coli YchN and TusD. TusBCD and the protein TusE are parts of sulfur relay system involved in thiouridine biosynthesis. DsrEFH interacts with DsrC, a TusE homologue encoded in the same operon. The conserved penultimate cysteine residue in the carboxy-terminus of DsrC is essential for the interaction. Here, we show that Cys78 of DsrE is strictly required for interaction with DsrC while Cys20 in the putative active site of DsrH is dispensable for that reaction. In summary, our findings point at the occurrence of sulfur transfer reactions during sulfur oxidation via the Dsr proteins.

Utilization of solid ‘elemental’ sulfur by the phototrophic purple sulfur bacterium Allochromatium vinosum: a sulfur K-edge X-ray absorption spectroscopy study

The purple sulfur bacterium Allochromatium vinosum can use elemental sulfur as an electron donor for anoxygenic photosynthesis. The elemental sulfur is taken up, transformed into intracellular sulfur globules and oxidized to sulfate. Commercially available "elemental" sulfur usually consists of the two species cyclo-octasulfur and polymeric sulfur. The authors investigated whether only one sulfur species is used or at least preferred when Alc. vinosum takes up elemental sulfur and forms globules. To this end, Alc. vinosum was cultivated photolithoautotrophically with two types of elemental sulfur that differed in their cyclo-octasulfur : polymeric sulfur ratio, as well as with pure polymeric sulfur. Sulfur speciation was analysed using X-ray absorption spectroscopy, and sulfate contents were determined by HPLC to quantify the amount of elemental sulfur being taken up and oxidized by Alc. vinosum. The results show that Alc. vinosum uses only the polymeric sulfur (sulfur chain) fraction of elemental sulfur and is probably unable to take up and form sulfur globules from cyclo-octasulfur. Furthermore, direct cell-sulfur contact appears to be necessary for uptake of elemental sulfur by Alc. vinosum.

Importance of the DsrMKJOP complex for sulfur oxidation in Allochromatium vinosum and phylogenetic analysis of related complexes in other prokaryotes

In the phototrophic sulfur bacterium Allochromatium vinosum, sulfur of oxidation state zero stored in intracellular sulfur globules is an obligate intermediate during the oxidation of sulfide and thiosulfate. The proteins encoded in the dissimilatory sulfite reductase (dsr) locus are essential for the oxidation of the stored sulfur. DsrMKJOP form a membrane-spanning complex proposed to accept electrons from or to deliver electrons to cytoplasmic sulfur-oxidizing proteins. In frame deletion mutagenesis showed that each individual of the complex-encoding genes is an absolute requirement for the oxidation of the stored sulfur in Alc. vinosum. Complementation of the DeltadsrJ mutant using the conjugative broad host range plasmid pBBR1-MCS2 and the dsr promoter was successful. The importance of the DsrMKJOP complex is underlined by the fact that the respective genes occur in all currently sequenced genomes of sulfur-forming bacteria such as Thiobacillus denitrificans and Chlorobaculum tepidum. Furthermore, closely related genes are present in the genomes of sulfate- and sulfite-reducing prokaryotes. A phylogenetic analysis showed that most dsr genes from sulfide oxidizers are clearly separated of those from sulfate reducers. Surprisingly, the dsrMKJOP genes of the Chlorobiaceae all cluster together with those of the sulfate/sulfite-reducing prokaryotes, indicating a lateral gene transfer at the base of the Chlorobiaceae.

The role of the sulfur globule proteins of Allochromatium vinosum: mutagenesis of the sulfur globule protein genes and expression studies by real-time RT-PCR.

During oxidation of reduced sulfur compounds, the purple sulfur bacterium Allochromatium vinosum stores sulfur in the periplasm in the form of intracellular sulfur globules. The sulfur in the globules is enclosed by a protein envelope that consists of the homologous 10.5-kDa proteins SgpA and SgpB and the smaller 8.5-kDa SgpC. Reporter gene fusions of sgpA and alkaline phosphatase showed the constitutive expression of sgpA in A. vinosum and yielded additional evidence for the periplasmic localization of the sulfur globules. Expression analysis of the wild-type sgp genes by quantitative RT-PCR using the LightCycler system showed the constitutive expression of all three sgp genes. The expression of sgpB and sgpC is significantly enhanced under photolithotrophic conditions. Interestingly, sgpB is expressed ten times less than sgpA and sgpC implying that SgpA and SgpC are the "main proteins" of the sulfur globule envelope. Mutants with inactivated sgpA or sgpB did not show any differences in comparison with the wild-type, i.e., the encoded proteins can replace each other, whereas inactivation of sgpC leads to the formation of considerably smaller sulfur globules. This indicates a role of SgpC for globule expansion. A sgpBC double mutant was unable to grow on sulfide and could not form sulfur globules, showing that the protein envelope is indispensible for the formation and deposition of intracellular sulfur.

Thialkalivibrio nitratireducens sp. nov., a nitrate-reducing member of an autotrophic denitrifying consortium from a soda lake.

Strain ALEN 2(T) was isolated from a mixed culture capable of complete autotrophic denitrification with thiosulfate as electron donor at pH 10; the mixed culture was enriched from sediment from Lake Fazda (Wadi Natrun, Egypt), a hypersaline alkaline lake. The isolate had large, non-motile, coccoid or barrel-shaped cells with intracellular sulfur globules. The bacterium was obligately chemolithoautotrophic. It grew with reduced sulfur compounds aerobically and anaerobically with nitrate as electron acceptor, nitrate being reduced to nitrite. It was moderately halophilic and obligately alkaliphilic. On the basis of genetic analysis and its unique phenotype, strain ALEN 2(T) (=DSM 14787(T)=UNIQEM 213(T)) is proposed as the type strain of a novel species of the genus Thialkalivibrio, Thialkalivibrio nitratireducens.

Thiobaca trueperi gen. nov., sp. nov., a phototrophic purple sulfur bacterium isolated from freshwater lake sediment.

Two strains of a novel species of phototrophic micro-organism were isolated from the sediments of a shallow, freshwater, eutrophic lake. Both strains grew photolithoheterotrophically with sulfide as an electron donor, transiently accumulating intracellular sulfur globules. Photolithoautotrophic growth was not observed. One strain was designated BCH(T) (the type strain) and was studied in most detail. Cells contained bacteriochlorophyll a, and the dominant carotenoid was lycopene. Cell suspensions were brown. The photosynthetic membranes had a vesicular arrangement. Acetate, propionate, pyruvate, succinate and fumarate were each used as electron donors and carbon sources in the presence of sulfide and bicarbonate. In the presence of light, growth did not occur with hydrogen, thiosulfate or iron(II). The optimum temperature for growth was between 25 and 30 degrees C, the maximum being 36 degrees C. The G+C content of the genomic DNA of strain BCH(T) was 63 mol%. Analysis of the 16S RNA genes showed that both strains belonged to the gamma-subclass of the Proteobacteria but were phylogenetically distinct from any described phototrophic organisms within the Chromatiaceae. On the basis of phylogenetic and physiological differences from other phototrophic microorganisms, strain BCH(T) is described as a novel species of a new genus, Thiobaca trueperi gen. nov., sp. nov.

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 approximately 500-microm-thick band at the oxic-anoxic interface, with a sharp border toward the oxic zone always positioned at approximately 10 microM O(2). Flux calculations yielded a molar conversion ratio S(tot)/O(2) of 2.03:1 (S(tot) = [H(2)S] + [HS(-)] + [S(2-)]) 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 microM O(2). 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 microM 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.

Physiology of purple sulfur bacteria forming macroscopic aggregates in Great Sippewissett Salt Marsh, Massachusetts

Purple bacterial aggregates found in tidal pools of Great Sippewissett Salt Marsh (Falmouth, Cape Cod, MA) were investigated in order to elucidate the ecological significance of cell aggregation. Purple sulfur bacteria were the dominant microorganisms in the aggregates which also contained diatoms and a high number of small rod-shaped bacteria. Urea in concentrations of ≥ 1 M caused disintegration of the aggregates while proteolytic enzymes, surfactants or chaotropic agents did not exhibit this effect. This suggests that polysaccharides in the embedding slime matrix stabilize the aggregate structure. In addition cell surface hydrophobicity is involved in aggregate formation. The concentration of dissolved oxygen decreased rapidly below the surface of aggregates while sulfide was not detected. The apparent respiration rate in the aggregates was high when the purple sulfur bacteria contained intracellular sulfur globules. In the presence of DCMU, respiration remained light-inhibited. Light inhibition disappeared in the presence of KCN. These results demonstrated that respiration in the aggregates is due mainly to purple sulfur bacteria. The concentration of bacteriochlorophyll (Bchl) a in the aggregates (0.205 mg Bchl a cm−3) was much higher than in the pool sediments but comparable to concentrations in microbial mats of adjacent sand flats. Purple aggregates may therefore originate in the microbial mats rather than in the pools themselves. Rapid sedimentation and high respiration rates of Chromatiaceae in the aggregates would prevent the inhibition of Bchl synthesis if aggregates were lifted off the sediment and up into the oxic pool water by tidal currents.

Continuous chemotrophic growth and respiration of Chromatiaceae species at low oxygen concentrations

Endogenous and maximum respiration rates of nine purple sulfur bacterial strains were determined. Endogenous rates were below 10 nmol O2 · (mg protein · min)-1 for sulfur-free cells and 15–35 nmol O2 · (mg protein · min)-1 for cells containg intracellular sulfur globules. With sulfide as electron-donating substrate respiration rates were considerably higher than with thiosulfate. Maximum respiration rates of Thiocystis violacea 2711 and Thiorhodovibrio winogradskyi SSP1 (254.8 and 264.2 nmol O2 · (mg protein · min)-1, respectively) are similar to those of aerobic bacteria. Biphasic respiration curves were obtained for sulfur-free cells of Thiocystis violacea 2711 and Chromatium vinosum 2811. In Thiocystis violacea the rapid and incomplete oxidation of thiosulfate was five times faster than the oxidation of stored sulfur. A high affinity of the respiratoty system for oxygen (K m =0.3–0.9 μM O2, V max=260 nmol O2 · (mg protein · min)-1 with sulfide as substrate, K m =0.6–2.4 μM O2, V max=14–40 nmol O2 · (mg protein · min)-1 with thiosulfate as substrate), for sulfide (K m =0.47 μM, V max=650 nmol H2S · (mg protein × min)-1, and for thiosulfate (K m =5–6 μM, V max =24–72 nmol S2O 2-3 · (mg protein · min)-1 was obtained for different strains. Respiration of Thiocystis violacea was inhibited by very low concentrations of NaCN (K i =1.7 μM) while CO concentrations of up to 300 μM were not inhibitory. The capacity for chemotrophic growth of six species was studied in continuous culture at oxygen concentrations of 11 to 67 μM. Thiocystis violacea 2711, Amoebobacter roseus 6611, Thiocapsa roseopersicina 6311 and Thiorhodovibrio winogradskyi SSP1 were able to grow chemotrophically with thiosulfate/acetate or sulfide/acetate. Chromatium vinosum 2811 and Amoebobacter purpureus ML1 failed to grow under these conditions. During shift from phototrophic to chemotrophic conditions intracellular sulfur and carbohydrate accumulated transiently inside the cells. During chemotrophic growth bacteriochlorophyll a was below the detection limit.

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 (SnO 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.