Identification of the plasmid-mobilization potential of the strain Klebsiella pneumoniae ozenae KIIIA isolated from a polluted aquatic environment

Adaptation in Toxic Environments: Arsenic Genomic Islands in the Bacterial Genus Thiomonas

Acid mine drainage (AMD) is a highly toxic environment for most living organisms due to the presence of many lethal elements including arsenic (As). Thiomonas (Tm.) bacteria are found ubiquitously in AMD and can withstand these extreme conditions, in part because they are able to oxidize arsenite. In order to further improve our knowledge concerning the adaptive capacities of these bacteria, we sequenced and assembled the genome of six isolates derived from the Carnoulès AMD, and compared them to the genomes of Tm. arsenitoxydans 3As (isolated from the same site) and Tm. intermedia K12 (isolated from a sewage pipe). A detailed analysis of the Tm. sp. CB2 genome revealed various rearrangements had occurred in comparison to what was observed in 3As and K12 and over 20 genomic islands (GEIs) were found in each of these three genomes. We performed a detailed comparison of the two arsenic-related islands found in CB2, carrying the genes required for arsenite oxidation and As resistance, with those found in K12, 3As, and five other Thiomonas strains also isolated from Carnoulès (CB1, CB3, CB6, ACO3 and ACO7). Our results suggest that these arsenic-related islands have evolved differentially in these closely related Thiomonas strains, leading to divergent capacities to survive in As rich environments.

Constitutive arsenite oxidase expression detected in arsenic-hypertolerant Pseudomonas xanthomarina S11

Pseudomonas xanthomarina S11 is an arsenite-oxidizing bacterium isolated from an arsenic-contaminated former gold mine in Salsigne, France. This bacterium showed high resistance to arsenite and was able to oxidize arsenite to arsenate at concentrations up to 42.72 mM As[III]. The genome of this strain was sequenced and revealed the presence of three ars clusters. One of them is located on a plasmid and is organized as an "arsenic island" harbouring an aio operon and genes involved in phosphorous metabolism, in addition to the ars genes. Neither the aioXRS genes nor a specific sigma-54-dependent promoter located upstream of aioBA genes, both involved in regulation of arsenite oxidase expression in other arsenite-oxidizing bacteria, could be identified in the genome. This observation is in accordance with the fact that no difference was observed in expression of arsenite oxidase in P. xanthomarina S11, whether or not the strain was grown in the presence of As[III].