Taxonomy, physiology and biochemistry of the Sulfur Bacteris
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Inorganic sulfur-oxidising Bacteria are present throughout the Proteobacteria and inhabit all environments of Earth. Despite these facts they are still poorly understood in terms of taxonomy, physiology, biochemistry and genetics. Using phylogenetic and chemotaxonomic analysis two species that were erroneously classified as Thiobacillus trautweinii spp. in 1921 and 1934 are in fact novel chemolithoheterotrophic species for which the names Pseudomonas trautweiniana sp. nov. and Achromobacter starkeyanus sp. nov. are proposed, respectively. These species were found to oxidise thiosulfate in a “fortuitous” manor when grown in continuous culture and increases in maximum theoretical growth yield (YMAX) and maximum specific growth rate (μMAX) were observed. Cytochrome c linked thiosulfate-dependent ATP production was confirmed in both species, confirming “true” chemolithoheterotrophy. Evidence is presented that the ATP concentration governs the benefits of chemolithoheterotrophy. There were significant changes in enzyme activities, including enzymes of the TCA cycle that might be affecting amino acid synthesis. This is strong evidence that chemolithoheterotrophy gives a strong physiological boost and evolutionary advantage over strictly heterotrophic species. An autotrophic species that was historically placed in Thiobacillus was also shown to be a novel species for which the name Thermithiobacillus parkerianus sp. nov. is proposed. The enzyme profiles of Thermithiobacillus parkerianus differed significantly between different inorganic sulfur growth substrates and was the first time all TCA cycle enzymes were assayed in a member of the Acidithiobacillia. The properties of thiosulfate dehydrogenase varied significantly between Pseudomonas sp. Strain T, Achromobacter sp. Strain B and Thermithiobacillus sp. ParkerM both in terms of optimal parameters and the effect of inhibitors. This evidence adds to the increasing body of work indicating there to be at least two thiosulfate dehydrogenases present in the Bacteria.