Hydrogenomics of the extremely thermophilic bacterium Caldicellulosiruptor saccharolyticus.

Caldicellulosiruptor saccharolyticus is an extremely thermophilic, gram-positive anaerobe which ferments cellulose-, hemicellulose- and pectin-containing biomass to acetate, CO(2), and hydrogen. Its broad substrate range, high hydrogen-producing capacity, and ability to coutilize glucose and xylose make this bacterium an attractive candidate for microbial bioenergy production. Here, the complete genome sequence of C. saccharolyticus, consisting of a 2,970,275-bp circular chromosome encoding 2,679 predicted proteins, is described. Analysis of the genome revealed that C. saccharolyticus has an extensive polysaccharide-hydrolyzing capacity for cellulose, hemicellulose, pectin, and starch, coupled to a large number of ABC transporters for monomeric and oligomeric sugar uptake. The components of the Embden-Meyerhof and nonoxidative pentose phosphate pathways are all present; however, there is no evidence that an Entner-Doudoroff pathway is present. Catabolic pathways for a range of sugars, including rhamnose, fucose, arabinose, glucuronate, fructose, and galactose, were identified. These pathways lead to the production of NADH and reduced ferredoxin. NADH and reduced ferredoxin are subsequently used by two distinct hydrogenases to generate hydrogen. Whole-genome transcriptome analysis revealed that there is significant upregulation of the glycolytic pathway and an ABC-type sugar transporter during growth on glucose and xylose, indicating that C. saccharolyticus coferments these sugars unimpeded by glucose-based catabolite repression. The capacity to simultaneously process and utilize a range of carbohydrates associated with biomass feedstocks is a highly desirable feature of this lignocellulose-utilizing, biofuel-producing bacterium.

Methanol utilizing Desulfotomaculum species utilizes hydrogen in a methanol-fed sulfate-reducing bioreactor.

A sulfate-reducing bacterium, strain WW1, was isolated from a thermophilic bioreactor operated at 65 degrees C with methanol as sole energy source in the presence of sulfate. Growth of strain WW1 on methanol or acetate was inhibited at a sulfide concentration of 200 mg l(-1), while on H2/CO2, no apparent inhibition occurred up to a concentration of 500 mg l(-1). When strain WW1 was co-cultured under the same conditions with the methanol-utilizing, non-sulfate-reducing bacteria, Thermotoga lettingae and Moorella mulderi, both originating from the same bioreactor, growth and sulfide formation were observed up to 430 mg l(-1). These results indicated that in the co-cultures, a major part of the electron flow was directed from methanol via H2/CO2 to the reduction of sulfate to sulfide. Besides methanol, acetate, and hydrogen, strain WW1 was also able to use formate, malate, fumarate, propionate, succinate, butyrate, ethanol, propanol, butanol, isobutanol, with concomitant reduction of sulfate to sulfide. In the absence of sulfate, strain WW1 grew only on pyruvate and lactate. On the basis of 16S rRNA analysis, strain WW1 was most closely related to Desulfotomaculum thermocisternum and Desulfotomaculum australicum. However, physiological properties of strain WW1 differed in some aspects from those of the two related bacteria.

Methanol utilization in defined mixed cultures of thermophilic anaerobes in the presence of sulfate.

We studied thermophilic sulfate reduction with methanol as electron donor in continuous cultures. Mixed cultures of selected microorganisms were used, representing different methanol degrading pathways followed by various trophic groups of microorganisms. Our results show that direct competition for methanol between a homoacetogen, Moorella thermoautotrophica, and a sulfate reducer, Desulfotomaculum kuznetsovii, is in favour of the sulfate reducer due to its affinity for methanol. Methanogenesis as a result of interspecies hydrogen transfer between D. kuznetsovii and a hydrogen-consuming methanogenic archaeon, Methanothermobacter thermoautotrophicus occurred only below 5 mM total sulfide. A similar result was obtained when M. thermoautotrophica was grown on methanol in the presence of Mb. thermoautotrophicus. Interestingly, D. kuznetsovii could coexist with a non-methanol-utilizing sulfate reducer (Thermodesulfovibrio species). Our data show that it is possible to maintain a dominant sulfate-reducing process with methanol as electron donor at 60 degrees C in mixed continuous cultures.

Isolation of thermophilic Desulfotomaculum strains with methanol and sulfite from solfataric mud pools, and characterization of Desulfotomaculum solfataricum sp. nov.

Four strains of thermophilic, endospore-forming, sulfate-reducing bacteria were enriched and isolated from hot solfataric fields in the Krafla area of north-east Iceland, using methanol and sulfite as substrates. Morphologically, these strains resembled thermophilic Desulfotomaculum species. The strains grew with alcohols, including methanol, with glucose and fructose as electron donors, and with sulfate, sulfite or thiosulfate as electron acceptors. For all four strains, the optimum temperature and pH for growth were 60 degrees C and pH 7.3, respectively; no added NaCl was required. Phylogenetic analysis based on partial 16S rRNA gene sequence comparisons showed high levels of similarity of the novel strains (>92 %) with Desulfotomaculum kuznetsovii and Desulfotomaculum luciae. However, DNA-DNA hybridization studies with D. kuznetsovii revealed that the four strains belonged to one novel species. A representative of this group of isolates, strain V21(T), is proposed as the type strain of a novel species of the spore-forming, sulfate-reducing genus Desulfotomaculum, namely Desulfotomaculum solfataricum (type strain V21(T)=DSM 14956(T)=CIP 107984(T)).