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.

An obligately anaerobic, spore-forming, acidophilic sulfate-reducing bacterium, strain SJ4(T), was isolated from an acid mining effluent decantation pond sediment sample (pH around 3.0). Cells were Gram negative, non-motile, curved rods occurring singly. Strain SJ4(T) grew at pH 3.6-5.5 with an optimum at pH 5.2. Strain SJ4(T) utilized H(2), lactate, pyruvate, glycerol, glucose, and fructose as electron donors. Lactate and glucose were weakly used. Sulfate was used as electron acceptors, but not sulfite, elemental sulfur, arsenate (V), and fumarate. The G + C content of genomic DNA was 42.3 mol% (HPLC). 16S rRNA gene sequence analysis indicated that strain SJ4(T) belonged to the genus Desulfosporosinus within the family Peptococcaceae in the phylum Firmicutes. The level of 16S rRNA gene sequence similarity with other Desulfosporosinus species was 94.7-96.2%, D. orientis DSM 765(T) (similarity of 96.2%) and D. auripigmenti DSM 13351(T) (similarity of 95%) being its closest relatives. DNA-DNA relatedness values with D. orientis and D. auripigmenti were 16.5 and 31.8%, respectively. On the basis of phenotypic, phylogenetic, and genetic characteristics, strain SJ4(T) represents a novel species within the genus Desulfosporosinus, for which the name Desulfosporosinus acidiphilus sp. nov. is proposed. The type strain is SJ4(T) (=DSM 22704(T) = JCM 16185(T)).

Aims: To select an autotrophic arsenic(III)-oxidizing population, named CASO1, and to evaluate the performance of the selected bacteria in reactors. Methods and Results: An As(III)-containing medium without organic substrate was used to select CASO1 from a mining environment. As(III) oxidation was studied under batch and continuous conditions. The main organisms present in CASO1 were identified with molecular biology tools. CASO1 exhibited significant As(III)-oxidizing activity between pH 3 and 8. The optimum temperature was 25°C. As(III) oxidation was still observed in the presence of 1000 mg l )1 As(III). In continuous culture mode, the As(III) oxidation rate reached 160 mg l )1 h )1 . The CASO1 consortium contains at least two organisms -strain b3, which is phylogenetically close to Ralstonia picketii, and strain b6, which is related to the genus Thiomonas. The divergence in 16S rDNA sequences between b6 and the closest related organism was 5AE9%, suggesting that b6 may be a new species. Conclusions: High As(III)-oxidizing activity can be obtained without organic nutrient supply, using a bacterial population from a mining environment. Significance and Impact of the Study: The biological oxidation of arsenite by the CASO1 population is of particular interest for decontamination of arsenic-contaminated waste or groundwater.

BackgroundThiomonas strains are ubiquitous in arsenic-contaminated environments. Differences between Thiomonas strains in the way they have adapted and respond to arsenic have never been studied in detail. For this purpose, five Thiomonas strains, that are interesting in terms of arsenic metabolism were selected: T. arsenivorans, Thiomonas spp. WJ68 and 3As are able to oxidise As(III), while Thiomonas sp. Ynys1 and T. perometabolis are not. Moreover, T. arsenivorans and 3As present interesting physiological traits, in particular that these strains are able to use As(III) as an electron donor.ResultsThe metabolism of carbon and arsenic was compared in the five Thiomonas strains belonging to two distinct phylogenetic groups. Greater physiological differences were found between these strains than might have been suggested by 16S rRNA/rpoA gene phylogeny, especially regarding arsenic metabolism. Physiologically, T. perometabolis and Ynys1 were unable to oxidise As(III) and were less arsenic-resistant than the other strains. Genetically, they appeared to lack the aox arsenic-oxidising genes and carried only a single ars arsenic resistance operon. Thiomonas arsenivorans belonged to a distinct phylogenetic group and increased its autotrophic metabolism when arsenic concentration increased. Differential proteomic analysis revealed that in T. arsenivorans, the rbc/cbb genes involved in the assimilation of inorganic carbon were induced in the presence of arsenic, whereas these genes were repressed in Thiomonas sp. 3As.ConclusionTaken together, these results show that these closely related bacteria differ substantially in their response to arsenic, amongst other factors, and suggest different relationships between carbon assimilation and arsenic metabolism.

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