Phylogenetic analysis on the arsenic-resistant bacteria isolated from three different freshwater environments

Several aquatic environments are arsenic (As)-contaminated by geochemical sources and by residues derived from industrial and agricultural activities. In the current study, arsenic-resistant bacterial strains were isolated from Lake Albano, the Tiber River and a freshwater well (Bassano Romano), three sites located in the Latium region, central Italy, in which volcanic formations and aquifers containing As contribute to water As contamination. Bacteria capable of either oxidising As(III) or reducing As(V) belonged, on the basis of the 16S rRNA gene sequences, to the Proteobacteria, Firmicutes and Bacteroidetes. Moreover, phylogenetic analysis conducted on the gene codifying the ArsB, an As(III) efflux membrane protein pump related to the arsenic resistance, suggested the occurrence of horizontal arsB transfer events for some of the examined environmental strains, even among taxa belonging to taxonomically distant bacteria. Overall, these results showed that in each of the environments investigated, bacteria related to the redox of As coexisted, confirming important roles of microbial populations in the speciation of As and increasing the knowledge in view of the bioremoving of As compounds.