Utilization of Serine, Leucine, Isoleucine, and Valine byThermoanaerobacter brockiiin the Presence of Thiosulfate orMethanobacteriumsp. as Electron Acceptors

Thermoanaerobacter brockiifermented serine to acetate and ethanol. It oxidized leucine to isovalerate, isoleucine to 2-methylbutyrate, and valine to isobutyrate only in the presence of thiosulfate, or when co-cultured withMethanobacteriumsp. This oxidative deamination was rendered thermodynamically possible by the ability ofT. brockiito reduce thiosulfate to sulfide or the transfer of reducing equivalents to the hydrogenotrophic methanogen. The results suggest thatT. brockiimay be of ecological significance in thermal environments in the turnover of amino acids, especially with thiosulfate or H₂-utilizing methanogens are present.     

The functional role of reduced inorganic sulfur compounds in the metabolism of the microaerophilic bacterium <Emphasis Type="Italic">Spirillum winogradskii</Emphasis>

Oxidation of reduced sulfur compounds by the microaerophilic sulfur bacterium spirillum winogradskii was found to occur only concomitantly with consumption of an organic substrate and was not linked to their utilization as electron donors in energy metabolism. No enzymes of dissimilatory sulfur metabolism were found in the cells of the sulfur bacterium oxidizing thiosulfate to tetrathionate; oxidation of thiosulfate and sulfide was caused by their reaction with reactive oxygen species (ROSs), mostly H₂O₂ produced in the course of aerobic growth. A decreased lytic effect of ROSs in the presence of thiosulfate resulted in a twofold increase in the cell yield under aerobic conditions and more efficient substrate utilization. The latter effect was caused by decreased expenditure of energy for the biosynthesis of oxygen-protective polysaccharides. The stimulatory effect of thiosulfate on the growth processes was due to the activation of a number of TCA cycle enzymes producing the intermediates for constructive metabolism, especially of the NADP-dependent malic enzyme. As a result of thiosulfate-induced synthesis of SH-containing cell components, the integral antioxidative activity increased 1.5-fold.Translated from Mikrobiologiya, Vol. 74, No. 1, 2005, pp. 17–25.Original Russian Text Copyright © 2005 by Podkopaeva, Grabovich, Dubinina.     

Hydrogen oxidation abilities in the presence of thiosulfate as electron acceptor within the genusThermoanaerobacter

Thermoanaerobacter (T.) brockii, T. ethanolicus, andT. thermohydrosulfuricus were tested for their capacities to oxidize H₂ in the presence of thiosulfate.T. brockii oxidized H₂ actively, whileT. ethanolicus andT. thermohydrosulfuricus oxidized it poorly. At the end of the exponential growth, H₂ was oxidized byT. brockii in the presence of an energy source and thiosulfate. This oxidative process improved the growth ofT. brockii. Thermoanaerobacter species could be divided into two groups with regard to their H₂ metabolism in the presence of thiosulfate. Thiosulfate reduction by species of the genusThermoanaerobacter is of significance in mineralizing organic matter in thermophilic environments.     

Oxidation of H2, organic compounds and inorganic sulfur compounds coupled to reduction of O2 or nitrate by sulfate-reducing bacteria

All of fourteen sulfate-reducing bacteria tested were able to carry out aerobic respiration with at least one of the following electron donors: H₂, lactate, pyruvate, formate, acetate, butyrate, ethanol, sulfide, thiosulfate, sulfite. Generally, we did not obtain growth with O₂ as electron acceptor. The bacteria were microaerophilic, since the respiration rates increased with decreasing O₂ concentrations or ceased after repeated O₂ additions. The amounts of O₂ consumed indicated that the organic substrates were oxidized incompletely to acetate; only Desulfobacter postgatei oxidized acetate with O₂ completely to CO₂. Many of the strains oxidized sulfite (completely to sulfate) or sulfide (incompletely, except Desulfobulbus propionicus); thiosulfate was oxidized only by strains of Desulfovibrio desulfuricans; trithionate and tetrathionate were not oxidized by any of the strains. With Desulfovibrio desulfuricans CSN and Desulfobulbus propionicus the oxidation of inorganic sulfur compounds was characterized in detail. D. desulfuricans formed sulfate during oxidation of sulfite, thiosulfate or elemental sulfur prepared from polysulfide. D. propionicus oxidized sulfite and sulfide to sulfate, and elemental sulfur mainly to thiosulfate. A novel pathway that couples the sulfur and nitrogen cycles was detected: D. desulfuricans and (only with nitrite) D. propionicus were able to completely oxidize sulfide coupled to the reduction of nitrate or nitrite to ammonia. Cell-free extracts of both strains did not oxidize sulfide or thiosulfate, but formed ATP during oxidation of sulfite (37 nmol per 100 nmol sulfite). This, and the effects of AMP, pyrophosphate and molybdate on sulfite oxidation, suggested that sulfate is formed via the (reversed) sulfate activation pathway (involving APS reductase and ATP sulfurylase). Thiosulfate oxidation with O₂ probably required a reductive first step, since it was obtained only with energized intact cells.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone - APS adenosine phosphosulfate or adenylyl sulfate     

Thiosulfate reduction and alanine production in glucose fermentation by members of the genus Coprothermobacter

Coprothermobacter platensis is an anaerobic, proteolytic, thermophilic bacterium, which is phylogenetically related to the genera Fervidobacterium and Thermotoga. The organism was found to reduce thiosulfate to sulfide during growth on carbohydrates and proteinaceous substrates. Growth on glucose was inhibited by hydrogen, but this inhibition was overcome by thiosulfate reduction, stirring, increasing the headspace volume and coculturing with a hydrogen-consuming methanogen. Alanine was detected during glucose fermentation, its formation was influenced by the hydrogen concentration in the gas phase suggesting an electron sink mechanism, as was previously reported for the phylogenetically related Thermotogales and the archaeal hyperthermophile Pyrococcus furiosus.     

Thiosulfate oxidation by a moderately thermophilic hydrogen-oxidizing bacterium, <Emphasis Type="Italic">Hydrogenophilus thermoluteolus</Emphasis>

The moderately thermophilic Betaproteobacterium, Hydrogenophilus thermoluteolus, not only oxidizes hydrogen, the principal electron donor for growth, but also sulfur compounds including thiosulfate, a process enabled by sox genes. A periplasmic extract of H. thermoluteolus showed significant thiosulfate oxidation activity. Ten genes apparently involved in thiosulfate oxidation (soxEFCDYZAXBH) were found on a 9.7-kb DNA fragment of the H. thermoluteolus chromosome. The proteins SoxAX, which represent c-type cytochromes, were co-purified from the cells of H. thermoluteolus; they enhanced the thiosulfate oxidation activity of the periplasmic extract when added to the latter.     

一株嗜热厌氧杆菌的分离、鉴定及其代谢特征

【目的】分离、保护油藏嗜热微生物资源,解析其主要的代谢特征。【方法】利用Hungte厌氧分离技术从大港油田埕海一区油层采出液中分离出厌氧菌株BF1。通过生理生化特征分析、16S rRNA基因序列比对与电化学分析,确定BF1的分类地位及其S元素代谢对腐蚀电流的影响。【结果】菌株BF1为严格嗜热厌氧革兰氏阴性杆菌,顶端产芽孢、不运动,菌体大小为0.42μm×(1.6 5.4)μm,单生、成对或成串生长。其温度生长范围为45°C 75°C(最适温度60°C);pH生长范围在4.5 8.5(最适pH 6.5)之间,比生长速率(μm)0.99 h 1,倍增时间为42 min。能利用葡萄糖、松三糖、棉子糖、甘露糖、乳糖、纤维二糖、果糖、核糖等碳水化合物,利用葡萄糖发酵的产物是乙醇、乙酸、CO2及少量的H2。菌株BF1能还原亚硫酸盐与硫代硫酸盐产生H2S,其耐受上限分别为50 mmol/L和75 mmol/L;还原硫代硫酸钠(50 mmol/L)后其极化电阻由2 099/cm2降低至776/cm2,腐蚀电流由9.936e-006 A提高至3.25e-005 A。细胞膜脂肪酸主要由高级饱和脂肪酸组成,含量最丰富的为十五烷酸占70.6%。菌株BF1的DNA(G+C)mol%含量为34.0%,其16S rRNA与Thermoanaerobacter pseudethanolicus DSM 2355T相似性最高,为98.3%,与T.brockii subsp.brockii DSM 1457T次之,为98.0%。菌株BF1的许多生理、生化特征与T.pseudethanolicus DSM 2355T和T.brockii subsp.brockii DSM 1457T有着明显的差别,如倍增时间、最适生长温度及底物利用等;而菌株BF1的细胞膜脂肪酸组成与T.pseude-thanolicus DSM 2355T也不相同。【结论】菌株BF1可能是Thermoanaerobacter属中的一个新种,其确切分类地位还需要进一步进行DNA分子杂交;其代谢元素硫提高腐蚀电流密度,可能会对油田管道与设备造成腐蚀。     

Sulfate formation via ATP sulfurylase in thiosulfate- and sulfite-disproportionating bacteria

Disproportionation of thiosulfate or sulfite to sulfate plus sulfide was found in several sulfate-reducing bacteria. Out of nineteen strains tested, eight disproportionated thiosulfate, and four sulfite. Growth with thiosulfate or sulfite as the sole energy source was obtained with three strains (Desulfovibrio sulfodismutans and the strains Bra02 and NTA3); additionally, D. desulfuricans strain CSN grew with sulfite but not with thiosulfate, although thiosulfate was disproportionated. Two sulfur-reducing bacteria, four phototrophic sulfur-oxidizing bacteria (incubated in the dark), and Thiobacillus denitrificans did not disproportionate thiosulfate or sulfite. Desulfovibrio sulfodismutans and D. desulfuricans CSN formed sulfate from thiosulfate or sulfite even when simultaneously oxidizing hydrogen or ethanol, or in the presence of 50 mM sulfate. The capacities of sulfate reduction and of thiosulfate and sulfite disproportionation were constitutively present. Enzyme activities required for sulfate reduction (ATP sulfurylase, pyrophosphatase, APS reductase, sulfite reductase, thiosulfate reductase, as well as adenylate kinase and hydrogenase) were detected in sufficient activities to account for the growth rates observed. ADP sulfurylase and sulfite oxidoreductase activities were not detected. Disproportionation was sensitive to the uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP) but not to the ATPase inhibitor dicyclohexylcarbodiimide (DCCD). It is proposed that during thiosulfate and sulfite disproportionation sulfate is formed via APS reductase and ATP sulfurylase, but not by sulfite oxidoreductase. Reversed electron transport must be assumed to explain the reduction of thiosulfate and sulfite by the electrons derived from APS reductase.Abbreviations CCCP Carbonylcyanide m-chlorophenylhydrazone - DCCD N,N-dicyclohexylcarbodiimide - APS adenosine 5-phosphosulfate (adenylylsulfate)     

Thiosulfate sulfur transferases (Rhodaneses) ofChlorobium vibrioforme f.thiosulfatophilum

Two enzymes containing thiosulfate sulfur transferase activity were purified fromChlorobium vibrioforme f.thiosulfatophilum by ion exchange chromatography, gel filtration and isoelectrofocusing. Enzyme I is a basic protein with an isoelectric point at pH 9.2 and has a molecular weight of 39,000. TheK _m-values for thiosulfate and cyanide of the purified basic protein were 0.25 mM (thiosulfate) and 5 mM (cyanide). Enzyme II is an acidic protein. The enzyme has an isoelectric point at pH 4.6–4.7 and a molecular weight of 34,000. TheK _m-values of the acidic protein were found to be 5 mM for thiosulfate and 125 mM for cyanide.In addition to thiosulfate sulfur transferase activity, cellfree extracts ofChlorobium vibrioforme f.thiosulfatophilum also contained low thiosulfate oxidase activity and negligible thiosulfate reductase activity. The percent distribution of thiosulfate sulfur transferase and thiosulfate oxidase activities in the organism was independent of the offered sulfur compound (thiosulfate, sulfide or both) in the medium.Abbreviations C Chlorobium - SDS sodium dodecylsulfate Dedicated to Prof. Dr. Norbert Pfennig on the occasion of his 60th birthday     

Capacity of chromatiaceae for chemotrophic growth. Specific respiration rates of Thiocystis violacea and Chromatium vinosum

The capacity for chemoautotrophic, mixotrophic and organotrophic growth in the dark was tested with 45 strains of 17 species (11 genera) of the Chromatiaceae. The auxanographic deep agar shake culture method was used; the gas phase contained 5% O₂ and 1% CO₂ in N₂. All strains tested of Chromatium vinosum, C. minus, C. violascens, C. gracile, Thiocystis violacea, Amoebobacter roseus, Thiocapsa roseopersicina gave positive growth responses under chemoautotrophic and mixotrophic conditions (extra carbon source acetate); one strain of Thiocapsa roseopersicina grew also organotrophically on acetate alone. No growth was obtained with the remaining 17 strains of ten species. None of the five type species (three genera) of the Chlorobiaceae grew under chemotrophic conditions. With Thiocystis violacea 2311 a growth yield of 11.3g dry weight per mol thiosulfate consumed was obtained under chemoautotrophic conditions; under mixotrophic conditions with acetate the yield increased to 69g dry weight per mol thiosulfate consumed. With Thiocystis violacea 2311 maximal specific respiration rates were obtained with thiosulfate as electron donor irrespective of the presence or absence of sulfur globules in the cells; organic substrates served as carbon sources only and did not support respiration. With Chromatium vinosum D utilization of thiosulfate was not constitutive; maximal respiration rates on thiosulfate were obtained only with thiosulfate grown cells containing sulfur globules. Respiration rates were further increased by malate, fumarate or propionate; these substrates also served as sole electron donors for respiration. Acetate and pyruvate were used as carbon sources only. The ecological significance of the chemotrophic metabolism is discussed.     

Mixotrophic growth of Thiobacillus A2 on acetate and thiosulfate as growth limiting substrates in the chemostat

During heterotrophic growth on acetate, in batch culture, the autotrophic growth potential of Thiobacillus A2, i.e. the capacity to oxidize thiosulfate and to fix carbon dioxide via the Calvin cycle, was completely repressed. The presence of thiosulfate in a batch culture with acetate as the organic substrate partly released the repression of the thiosulfate oxidizing system. Cultivation of the organism in continuous culture at a dilution rate of 0.05 h^-1 with different concentration ratios of thiosulfate and acetate in the reservoir medium led to mixotrophic growth under dual substrate limitation. Growth on the different mixtures of acetate and thiosulfate yielded upto 30% more cell dry weight than predicted from the growth yields on comparable amounts of these substrates separately. The extent to which the carbon dioxide fixation capacity and the maximum thiosulfate and acetate oxidation capacity are repressed appeared to be a function of the thiosulfate to acetate concentration ratio in the reservoir medium. The results of ¹⁴C-acetate assimilation experiments and of gas-analysis demonstrated that the extent to which acetate was assimilated depended also on the substrate ratio in the inflowing medium. Under the different growth conditions surprisingly little variation was found in some tri-carboxylic acid cycle enzyme activities. Cultivation of T. A2 at different growth rates with a fixed mixture of thiosulfate (18 mM) and acetate (11 mM) in the medium, showed that dual substrate limitation occured at dilution rates ranging from 0.03–0.20 h^-1.Abbreviations PPO 2,5-diphenoloxazol - RubPCase Ribulose-1,5-bisphophate carboxylase - Tris tris (hydroxymethyl) aminomethane - EDTA ethylenediaminetetra-acetic acid     

Oxidation of organic compounds to CO2 with sulfur or thiosulfate as electron acceptor in the anaerobic hyperthermophilic archaea Thermoproteus tenax and Pyrobaculum islandicum proceeds via the citric acid cycle

The oxidation of organic compounds with elemental sulfur or thiosulfate as electron acceptor was studied in the anaerobic hyperthermophilic archaea Thermoproteus tenax and Pyrobaculum islandicum. T. tenax was grown on either glucose or casamino acids and sulfur; P. islandicum on peptone and either elemental sulfur or thiosulfate as electron acceptor. During exponential growth only CO₂ and H₂S rather than acetate, alanine, lactate, and succinate were detected as fermentation products of both organisms; the ratio of CO₂/H₂S formed was 1:2 with elemental sulfur and 1:1 with thiosulfate as electron acceptor. Cell extracts of T. tenax and P. islandicum contained all enzymes of the citric acid cycle in catabolic activities: citrate synthase, aconitase, isocitrate dehydrogenase (NADP⁺-reducing), oxoglutarate: benzylviologen oxidoreductase, succinyl-CoA synthetase, succinate dehydrogenase, fumarase and malate dehydrogenase (NAD⁺-reducing). Carbon monoxide dehydrogenase activity was not detected. We conclude that in T. tenax and P. islandicum organic compounds are completely oxidized to CO₂ with sulfur or thiosulfate as electron acceptor and that acetyl-CoA oxidation to CO₂ proceeds via the citric acid cycle.     

Formation of thionates by freshwater and marine strains of sulfate-reducing bacteria

The formation of thionates (thiosulfate, trithionate and tetrahionate) during the reduction of sulfate or sulfite was studied with four marine and four freshwater strains of sulfate-reducing bacteria. Growing cultures of two strains of the freshwater species Desulfovibrio desulfuricans formed up to 400 M thiosulfate and 100 M trithionate under conditions of electron donor limitation. Tetrathionate was observed in lower concentrations of up to 30 M. Uncoupler-treated washed cells of the four freshwater strains formed thiosulfate and trithionate at low electron donor concentrations with sulfite in excess. In contrast, only one of four marine strains formed thionates. The freshwater strain Desulfobulbus propionicus transformed sulfite almost completely to thiosulfate and trithionate. The amounts produced increased with time, concentration of added sulfite and cell density. Tetrathionate was detected only occasionally and in low concentrations, and was probably formed by chemical oxidation of thiosulfate. The results confirm the diversity of the sulfite reduction pathways in sulfate-reducing bacteria, and suggest that thiosulfate and trithionate are normal by-products of sulfate reduction.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone     

Desulfomonile tiedjei gen. nov. and sp. nov., a novel anaerobic,dehalogenating, sulfate-reducing bacterium

An anaerobic, dehalogenating, sulfate-reducing bacterium, strain DCB-1, is described and nutritionally characterized. The bacterium is a Gram-negative, nonmotile, non-sporeforming large rod with an unusual morphological feature which resembles a collar. The microorganism reductively dehalogenates meta substituted halobenzoates and also reduces sulfate, sulfite and thiosulfate as electron acceptors. The bacterium requires nicotinamide, 1,4-naphthoquinone and thiamine for optimal growth in a defined medium. The microorganism can grow autotrophically on H₂:CO₂ with sulfate or thiosulfate as terminal electron acceptors. It can also grow heterotrophically with pyruvate, several methoxybenzoates, formate plus sulfate or benzoate plus sulfate. It ferments pyruvate to acetate and lactate in the absence of other electron acceptors. The bacterium is inhibited by MoO _inf4 ^sup2- or SeO _inf4 ^sup2- as well as tetracycline, chloramphenicol, kanamycin or streptomycin. Cytochrome c₃ and desulfoviridin have been purified from cells grown in defined medium. 16S rRNA sequence analysis indicates the organism is a new genus of sulfate-reducing bacteria in the delta subdivision of the class Proteobacteria. We propose that the strain be named Desulfomonile tiedjei.Non-standard abbreviations PIPES piperazine-N,N-bis[2-ethanesulfonic acid] - MES 2-[N-morpholino]ethanesulfonic acid - TES N-tris[hydroxymethyl]methyl-2-aminoethanesulfonic acid - HQNO 2-N-heptyl-4-hydroxy-quinoline-N-oxide - CCCP carbonyl-cyanide-m-chlorophenylhydrazine - CM carboxymethyl     

Anaerobic degradation of 1,3-propanediol by sulfate-reducing and by fermenting bacteria

Three strains of strictly anaerobic Gram-negative, non-sporeforming, motile bacteria were enriched and isolated from freshwater sediments with 1,3-propanediol as sole energy and carbon source. Strain OttPdl was a sulfate-reducing bacterium which grew also with lactate, ethanol, propanol, butanol, 1,4-butanediol, formate or hydrogen plus CO₂, the latter only in the presence of acetate. In the absence of sulfate, most of these substrates were fermented to the respective fatty acids in syntrophic cooperation with Methanospirillum hungatei. Sulfur, thiosulfate, or sulfite were reduced, nitrate not. The other two isolates degraded propanediol only in coculture with Methanospirillum hungatei. Strain OttGlycl grew in pure culture with acetoin and with glycerol in the presence of acetate. Strain WoAcl grew in pure culture only with acetoin. Both strains did not grow with other substrates, and did not reduce nitrate, sulfate, sulfur, thiosulfate or sulfite. The isolates were affiliated with the genera Desulfovibrio and Pelobacter. The pathways of propanediol degradation and the ecological importance of this process are discussed.     

Regulation of Metabolic and Electron Transport Pathways in the Freshwater Bacterium Beggiatoa leptomitiformis D-402

The biomass yield of freshwater filamentous sulfur bacteria of the genus Beggiatoa, when grown lithoheterotrophically or mixotrophically, has been shown to increase 2 to 2.5 times under microaerobic conditions (0.12 mg/l oxygen) as compared to aerobic conditions (9 mg/l oxygen). The activity of the glyoxylate cycle key enzymes have been found to increase two to three times under microaerobic conditions (at an O₂ concentration of 2 mg/l), and the activities of the sulfur metabolism enzymes increased three to five times (at an O₂ concentration of 0.1–0.5 mg/l). It has also been found that, under microaerobic conditions, thiosulfate was almost completely oxidized to sulfate by the bacteria, without accumulation of intermediate metabolites. At the same time, a 2- to 15-fold decrease in the activities of the tricarboxylic acid cycle enzymes involved in the reduction of NAD and FAD was observed. Reorganization of the respiratory chain after changes in aeration and type of nutrition was also observed. It has been found that, in cells grown heterotrophically, the terminal part of the respiratory chain contained an aa ₃-type oxidase, whereas, during mixotrophic, lithoheterotrophic, and autotrophic growth, aa ₃-type oxidase synthesis was inhibited, and the synthesis of a cbb ₃-type oxidase, which is induced under microaerobic conditions, was activated. The gene of the catalytic subunit CcoN of the cbb ₃-type oxidase was sequenced and proved to be highly homologous to the corresponding genes of other proteobacteria.__________Translated from Mikrobiologiya, Vol. 74, No. 4, 2005, pp. 452–459.Original Russian Text Copyright © 2005 by Muntyan, Grabovich, Patritskaya, Dubinina.     

Nitrogen fixation activity of a filamentous,nonheterocystous cyanobacterium in the presence and absence of exogenous,organic substrates

Gallionella ferruginea is able to utilize Fe(II) and the reduced sulfur compounds sulfide and thiosulfate as electron donor and energy source. Tetrathionate and elemental sulfur, on the other hand, are not metabolized. In sulfide-O₂ microgradient cultures G. ferruginea grows at the interface between the oxidizing and the reducing zones. Optimal growth depends on low oxygen and sulfide concentrations. Establishing within the gradient protects the bacterium from too high sulfide concentrations. G. ferruginea excretes extracellular polymeric substances (EPS). While in FeS-gradient cultures 2×10⁶ cells/ml were obtained the bacterial mass could be increased to 1–3×10⁸ cells/ml in shaken batch cultures using thiosulfate as substrate. A further increase of bacterial mass by adding an organic carbon source was not possible confirming that G. ferruginea is an obligate autotrophic organism. When growing on sulfide or thiosulfate the otherwise characteristic twisted stalk consisting of ferric hydroxide is lacking. It is thus shown to be a metabolic end product of Fe(II) oxidation rather than metabolically active cellular material.     

Thiosulfate and tetrathionate degradation as well as biofilm generation by Thiobacillus intermedius and Thiobacillus versutus studied by microcalorimetry,HPLC, and ion-pair chromatography

The growth of Thiobacillus (T.) intermedius strain K12 and Thiobacillus versutus strain DSM 582 on thiosulfate and tetrathionate was studied combining on-line measurements of metabolic activity and sulfur compound analysis. Most results indicate that T. intermedius oxidized thiosulfate via tetrathionate to sulfate. Concomittantly, sulfur compound intermediates like triand pentathionate were detectable. The formation is probably the result of highly reactive sulfane monosulfonic acids. The formation of tetrathionate allows the cells to buffer temporarily the proton excretion from sulfuric acid production. With T. versutus intermediate sulfur compounds were not detectable, however, sulfur was detectable. The possibility of a thiosulfate oxidation via dithionate, S₂O _inf6 ^sup2- , is discussed. The on-line measurement of metabolic activity by microcalorimetry enabled us to detect that cells of T. intermedius adhere to surfaces and produce a biofilm by a metabolic process whereas those of T. versutus fail to do so. The importance of the finding is discussed.     

Formation of thiosulfate and trithionate during sulfite reduction by washed cells of Desulfovibrio desulfuricans

Deenergized cells of Desulfovibrio desulfuricans strain Essex 6 formed trithionate and thiosulfate during reduction of sulfite with H₂ or formate. The required conditions were pretreatment with the uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP), low concentration of the electron donor H₂ or formate (25–200 M) and the presence of sulfite in excess (>250 M). The cells formed up to 20 M thiosulfate, and variable amounts of trithionate (0–9 M) and sulfide (0–62 M). Tetrathionate was not produced. Sulfate could not replace sulfite in these experiments, as deenergized cells cannot activate sulfate. However, up to 5 M thiosulfate was produced by cells growing with H₂ and excess sulfate in a chemostat. Micromolar concentrations of trithionate were incompletely reduced to thiosulfate and sulfide by washed cells in the presence of CCCP. Millimolar trithionate concentrations blocked the formation of sulfide, even in the absence of CCCP, and caused thiosulfate accumulation; sulfide formation from sulfate, sulfite or thiosulfate was stopped, too. Trithionate reduction with H₂ in the presence of thiocyanate was coupled to respiration-driven proton translocation (extrapolated H⁺/H₂ ratios of 1.5±0.6). Up to 150 M trithionate was formed by washed cells during oxidation of sulfite plus thiosulfate with ferricyanide as electron acceptor (reversed trithionate reductase activity). Cell breakage resulted in drastic decrease of sulfide formation. Cell-free extract reduced sulfite incompletely to trithionate, thiosulfate, and sulfide. Thiosulfate was reduced stoichiometrically to sulfite and sulfide (thiosulfate reductase activity). The formation of sulfide from sulfite, thiosulfate or trithionate by cell-free extract was blocked by methyl viologen, leading to increased production of thiosulfate plus trithionate from sulfite, or increased thiosulfate formation from trithionate. Our study demonstrates for the first time the formation of intermediates during sulfite reduction with whole cells of a sulfate-reducing bacterium oxidizing physiological electron donors. All results are in accordance with the trithionate pathway of sulfite reduction.With gratitude dedicated to Prof. Dr. Norbert Pfennig on occasion of his 65th birthday     

Competition between the facultatively chemolithotrophic Thiobacillus A2, an obligately chemolithotrophic Thiobacillus and a heterotrophic spirillum for inorganic and organic substrates

Competition in a chemostat between the versatile Thiobacillus A2 and the specialized T. neapolitanus for thiosulfate as the sole growth-limiting substrate, led to dominance of the specialized over the versatile organism, at dilution rates 0.025 h^-1. Increasing concentrations of acetate or glycollate in the thiosulfate medium caused increased relative numbers of T. A2 in steady states at D=0.07 h^-1. Eventually, with 10–12 mmol of organic substrate per litre, complete dominance of T. A2 over T. neapolitanus occurred.Mixed cultures of T. A2 and a specialized spirillumshaped heterotroph, competing for acetate as sole growth-limiting substrate resulted in complete dominance of the heterotroph at dilution rates of 0.07 and 0.15 h^-1. In this case increasing concentrations of thiosulfate in the acetate medium, up to 10 mM, eventually led to the elimination of the heterotroph.These results have been interpreted as evidence that T. A2 was growing mixotrophically. As the concentration of the second substrate was raised, the number of T. A2 cells increased and as a result T. A2 consumed an increasing portion of the common substrate.In mixed chemostat cultures containing all three organisms, T. A2 could maintain itself with all tested ratios of acetate and thiosulfate in the inflowing medium. The heterotroph was excluded from the culture below a relatively low acetate to thiosulfate ratio, whilst above a relatively high acetate to thiosulfate ratio T. neapolitanus was completely eliminated.These results were discussed in relation to the ecological niche of Thiobacillus A2-type organisms.