Bacteria of the Thiomonas genus are ubiquitous in extreme environments, such as arsenic-rich acid mine drainage (AMD). The genome of one of these strains, Thiomonas sp. 3As, was sequenced, annotated, and examined, revealing specific adaptations allowing this bacterium to survive and grow in its highly toxic environment. In order to explore genomic diversity as well as genetic evolution in Thiomonas spp., a comparative genomic hybridization (CGH) approach was used on eight different strains of the Thiomonas genus, including five strains of the same species. Our results suggest that the Thiomonas genome has evolved through the gain or loss of genomic islands and that this evolution is influenced by the specific environmental conditions in which the strains live. Recent advances in the field of arsenic microbial metabolism have revealed that bacteria colonize a large panel of highly contaminated environments. Belonging to the order of Burkholderiales, Thiomonas strains are ubiquitous in arsenic-contaminated environments. The genome of one of them, i.e. Thiomonas sp. 3As, was deciphered and compared to the genome of several other Thiomonas strains. We found that their flexible gene pool evolved to allow both the surviving and growth in their peculiar environment. In particular, the acquisition by strains of the same species of different genomic islands conferred heavy metal resistance and metabolic idiosyncrasies. Our comparative genomic analyses suggest that the natural environment influences the genomic evolution of these bacteria. Importantly, these results highlight the genomic variability that may exist inside a taxonomic group, enlarging the concept of bacterial species.

A new primer set was designed to specifically amplify ca. 1,100 bp of aoxB genes encoding the As(III) oxidase catalytic subunit from taxonomically diverse aerobic As(III)-oxidizing bacteria. Comparative analysis of AoxB protein sequences showed variable conservation levels and highlighted the conservation of essential amino acids and structural motifs. AoxB phylogeny of pure strains showed well-discriminated taxonomic groups and was similar to 16S rRNA phylogeny. Alphaproteobacteria -, Betaproteobacteria -, and Gammaproteobacteria -related sequences were retrieved from environmental surveys, demonstrating their prevalence in mesophilic As-contaminated soils. Our study underlines the usefulness of the aoxB gene as a functional marker of aerobic As(III) oxidizers.

A novel marine sulfate-reducing bacterium, strain CV2803^T, which is able to oxidize aliphatic hydrocarbons, was isolated from a hydrocarbon-polluted marine sediment (Gulf of Fos, France). The cells were rod-shaped and slightly curved, measuring 0·6×2·2–5·5 μm. Strain CV2803^Tstained Gram-negative and was non-motile and non-spore-forming. Optimum growth occurred in the presence of 24 g NaCl l⁻¹, at pH 7·5 and at a temperature between 28 and 35 °C. Strain CV2803^Toxidized alkanes (from C₁₃to C₁₈) and alkenes (from C₇to C₂₃). The DNA G+C content was 41·4 mol%. Comparative sequence analyses of the 16S rRNA gene and dissimilatory sulfite reductase (dsrAB) gene and those of other sulfate-reducing bacteria, together with its phenotypic properties, indicated that strain CV2803^Twas a member of a distinct cluster that contained unnamed species. Therefore, strain CV2803^T(=DSM 15576^T=ATCC BAA-743^T) is proposed as the type strain of a novel species in a new genus,Desulfatibacillum aliphaticivoransgen. nov., sp. nov.