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Filamentous iron oxides accumulating bacteria Sphaerotilus natans subsp. natans and S. natans subsp. sulfidivorans were described as subspecies based on 99.7% identity of their 16S rRNA sequences, in spite of important physiological difference. The ANI between their genomes was 94.7%, which indicate their assignment to different species. S. natans subsp. sulfidivorans and S. montanus possess genes for a complete SOX system, while S. natans subsp. natans encode only SoxYZ. There are genes for the Calvin cycle in the genomes of S. hippei DSM 566 T , S. natans subsp. sulfidivorans D-501 T , and S. montanus HS T . Lithoautotrophy on reduced sulfur compounds is probably possible for S. natans subsp. sulfidivorans and S. montanus, but not for S. natans subsp. natans. Considering significant differences in the genome characteristics and metabolic potential of S. natans subsp. sulfidivorans and S. natans subsp. natans, we propose their classification as different species, S. natans and S. sulfidivorans sp. nov.

Metabolically microorganisms are diverse, and they are capable of transforming almost every known group of chemical compounds present in coal and oil in various forms. In this milieu, one of the important microbial metabolic processes is the biodesulfurization [cleavage of carbon-sulfur (C-S) bond] of thiophenic compounds, such as dibenzothiophene (DBT), which is the most abundant form of organic sulfur present in fossil fuels. In the current study, ten newly isolated bacterial isolates, designated as species of genera Gordonia, Amycolatopsis, Microbacterium and Mycobacterium, were enriched from different samples in the presence of DBT as a sole source of organic sulfur. The HPLC analysis of the DBT grown cultures indicated the consumption of DBT and accumulation of 2-hydroxybiphenyl (2-HBP). Detection of 2-HBP, a marker metabolite of 4S (sulfoxide-sulfone-sulfinate-sulfate) pathway, suggested that the newly isolated strains harbored metabolic activity for DBT desulfurization through the cleavage of C-S bond. The maximum 2-HBP formation rate was 3.5 µmol/g dry cell weight (DCW)/h. The phylogenetic analysis of the new isolates showed that they had diverse distribution within the phylogenetic tree and formed distinct clusters, suggesting that they might represent strains of already reported species or they were altogether new species. Estimates of evolutionary divergence showed high level of nucleotide divergence between the isolates within the same genus. The new isolates were able to use a range of heterocyclic sulfur compounds, thus making them suitable candidates for a robust biodesulfurization system for fossil fuels.

In this study, a Candida digboiensis strain was isolated from a heap leaching plant in Zambia and used in double-layer agar plate to efficiently isolate and purify leaching bacteria. Unlike Acidiphilium sp., the yeast strain was tetrathionate tolerant and could metabolize a great range of organic compounds including organic acids. These properties allowed the yeast strain to enable and fasten the growth of iron and sulfur oxidizers on double-layer agar plate. The isolates were identified as Acidithiobacillus ferrooxidans FOX1, Leptospirillun ferriphilum BN, and Acidithiobacillus thiooxidans ZMB. These three leaching bacteria were inhibited by organic acids such as acetic and propionic acids; however, their activities were enhanced by Candida digboiensis NB under dissolved organic matter stress.

Acidithiobacillus ferrooxidans is a mesophilic, acidophilic, chemolithoautotrophic bacterium that obtains energy from the oxidation of ferrous iron (Fe2+), elemental sulfur and reduced sulfur compounds. The industrial interest in A. ferrooxidans resides in its capacity to oxidize insoluble metal sulfides into soluble metal sulfates, thus allowing the recovery of the desired metals from low-grade sulfide ores. In the present work, RNA arbitrarily primed PCR (RAP-PCR) was performed to identify cDNAs differentially expressed in A. ferrooxidans cells grown in the presence of Fe2+ and cells maintained for 24 h in the presence of the copper sulfides bornite and chalcopyrite. Eighteen cDNAs corresponding to genes with known function were identified, and their relative expression was further characterized by real-time quantitative PCR. Bornite had a mild effect on the expression of the 18 genes analyzed. None of these genes was down-regulated and among the few genes up-regulated, it is worth mentioning lepA and def-2 that are involved in protein synthesis. Chalcopyrite presented the most significant changes. Five genes related to protein processing were down-regulated, and another 5 genes related to the transport system were up-regulated. The up- and down-regulation of these genes in the presence of bornite and chalcopyrite could be due to alterations in the ideal pH, presence of copper ions in solution and nutrient limitation. The results suggest that gene expression modulation might be important for the A. ferrooxidans early response to copper sulfides.

The influence of reduced sulfur compounds (including stored S(0)) on H(2) evolution/consumption reactions in the purple sulfur bacterium, Thiocapsa roseopersicina BBS, was studied using mutants containing only one of the three known [NiFe] hydrogenase enzymes: Hox, Hup or Hyn. The observed effects depended on the kind of hydrogenase involved. The mutant harbouring Hox hydrogenase was able to use S(2)O (3) (2-) , SO (3) (2-) , S(2-) and S(0) as electron donors for light-dependent H(2) production. Dark H(2) evolution from organic substrates via Hox hydrogenase was inhibited by S(0). Under light conditions, endogenous H(2) uptake by Hox or Hup hydrogenases was suppressed by S compounds. CO(2)-dependent H(2) uptake by Hox hydrogenase in the light required the additional presence of S compounds, unlike the Hup-mediated process. Dark H(2) consumption via Hyn hydrogenase was connected to utilization of S(0) as an electron acceptor and resulted in the accumulation of H(2)S. In wild type BBS, with high levels of stored S(0), dark H(2) production from organic substrates was significantly lower, but H(2)S accumulation significantly higher, than in the mutant GB1121(Hox(+)). There is a possibility that H(2) produced via Hox hydrogenase is consumed by Hyn hydrogenase to reduce S(0).

Methylated sulfur compounds such as dimethylsulfoniopropionate, dimethylsulfide, methanethiol, and other methylated sulfur compounds can act as sources of carbon and energy for the growth under anoxic conditions of a number of sulfate-reducing bacteria and methanogenic archaea. We summarise the range of degradative reactions that do or might occur in such organisms, and present thermodynamic data for these processes. These data enable estimates of the feasibility of the reactions as growth-supporting systems, and of the possible maximum growth yields of the bacteria and archaea catalysing them. We compare our new estimates with the few data that are currently available from the literature, and show that some published growth-yield assessments need reevaluation.

Washed cells of Desulfovibrio vulgaris strain Marburg (DSM 2119) reduced oxygen to water with H(2) as electron donor at a mean rate of 253 nmol O(2) min(-1) (mg protein)(-1). After separating the periplasm from the cells, more than 60% of the cytochrome c activity and 90% of the oxygen-reducing activity were found in the periplasmic fraction. Oxygen reduction and the reduction of cytochrome c with H(2) were inhibited by CuCl(2). After further separation of the periplasm by ultrafiltration (exclusion sizes 30, 50, and 100 kDa), oxygen reduction with H(2) occurred with the retentates only. Ascorbate plus tetramethyl-p-phenylenediamine (TMPD), however, were also oxidized by the filtrates. The stoichiometry of 1 mol O(2) reduced per 2 mol ascorbate oxidized indicated the formation of water. Our experiments present evidence that in D. vulgaris periplasmic hydrogenase and cytochrome c play a major role in oxygen reduction. Preliminary studies with other Desulfovibrio species indicated a similar function of periplasmic c-type cytochromes in D. desulfuricans CSN and D. termitidis KH1.

We previously demonstrated that periodic H2S production during aerobic continuous culture of Saccharomyces cerevisiae resulted in ultradian respiratory oscillation, and that H2S production was dependent on the activity of sulfate uptake and the level of sulfite. To investigate the mechanism of regulation of the sulfate assimilation pathway and of respiratory oscillation, several amino acids were pulse-injected into cultures during respiratory oscillation. Injection of sulfur amino acids or their derivatives perturbed respiratory oscillation, with changes in the H2S production profile. Four major regulators of H2S production in the sulfate assimilation pathway and respiratory oscillation were identified: (1) O-acetylhomoserine, not O-acetylserine, as a sulfide acceptor, (2) homoserine/threonine as a regulator of O-acetylhomoserine supply, (3) methionine/S-adenosyl methionine as a negative regulator of sulfate assimilation, and (4) cysteine (or its derivatives) as an essential regulator. The results obtained after the addition of DL-propargylglycine (5 microM and 100 microM) and cystathionine (50 microM) suggested that the intracellular cysteine level and cystathionine gamma-lyase, rather than methionine/S-adenosylmethionine, play an essential role in the regulation of sulfate assimilation and respiratory oscillation. Based on these results and those of our previous reports, we propose that periodic depletion of cysteine (or its derivatives), which is involved in the detoxification of toxic materials originating from respiration, causes periodic H2S production.