Sulfobacillus thermotolerans: new insights into resistance and metabolic capacities of acidophilic chemolithotrophs

Abstract

AbstractThe first complete genome of the biotechnologically important speciesSulfobacillus thermotoleranshas been sequenced. Its 3 317 203-bp chromosome contains an 83 269-bp plasmid-like region, which carries heavy metal resistance determinants and the rusticyanin gene. Plasmid-mediated metal resistance is unusual for acidophilic chemolithotrophs. Moreover, most of their plasmids are cryptic and do not contribute to the phenotype of the host cells. A polyphosphate-based mechanism of metal resistance, which has been previously unknown in the genusSulfobacillusor other Gram-positive chemolithotrophs, potentially operates in twoSulfobacillusspecies. The methylcitrate cycle typical for pathogens and identified in the genusSulfobacillusfor the first time can fulfill the energy and/or protective function inS. thermotoleransKr1 and two otherSulfobacillusspecies, which have incomplete glyoxylate cycles. It is notable that the TCA cycle, disrupted in allSulfobacillusisolates under optimal growth conditions, proved to be complete in the cells enduring temperature stress. An efficient antioxidant defense system givesS. thermotoleransanother competitive advantage in the microbial communities inhabiting acidic metal-rich environments. The genomic comparisons revealed 80 unique genes in the strain Kr1, including those involved in lactose/galactose catabolism. The results provide new insights into metabolism and resistance mechanisms in theSulfobacillusgenus and other acidophiles.