In this study, ACR3(1) and ACR3(2) appeared to be mostly associated

with high arsenite resistance since they were only identified from the high and intermediate arsenic-contaminated sites, while arsB was found in all three sites. One explanation is that ACR3 may have a higher affinity and veloCity to extrude arsenite than arsB and thus seems to be more effective. Heavy metal contaminated environments were shown to provide a strong selective pressure for transfer of related resistance genes within soil systems [44]. In this study, aoxB and ACR3(1) appeared to be more stable than ACR3(2) and arsB since phylogenetic discrepancies between 16S rRNA genes Selleckchem AZD6738 and ACR3(2)/arsB were found which supported HGT events of ACR3(2) and arsB. Most of the HGT occurred in strains identified from the highly arsenic-contaminated TS soil [6 ACR3(2)]. This indicates that arsenite learn more transporter genes may be horizontally transferred and increasingly present in a microbial population under conditions of long-term elevated arsenic stress. It is important to note

that HGT occurred in somewhat closely related species in this study, however, this does not detract from the suggestion of HGT and it is likely that the HGT events occurred between these closely related species. Martinez et al. [45] reported that PIB-Type ATPases (pbrA/cadA/zntA) were broadly transferred in Arthrobacter and Bacillus in radionuclide and metal contaminated soils. Jackson and Dugas [46]

also suggested that horizontally transferred arsC resulted in the diversities and complexities of arsenate reductase during its evolution. Excluding arsC, other genes related to arsenic resistance (e.g. arsA, arsB/ACR3) had not been reported as being transferred by HGT. To our knowledge, this is the first study to report widespread horizontal transfer of arsenite transporter genes. The HGT event and subsequent maintenance may have occurred increasingly under the high arsenic pressure [47] and resulted in plastic selleck chemical changes in microbial diversity. Conclusion This work investigates the distribution CYTH4 and diversity of microbial arsenite-resistant species in soils representing three different levels of arsenic contamination, and further studies the arsenite resistance and arsenic transforming genes of these species. Our research provides valuable information of microbial species and genes responsible for arsenite oxidation and resistance, and increases knowledge of the diversity and distribution of the indigenous bacteria that may be stimulated for successful bioremediation of arsenic contamination. Methods Site description and soil sample collection Four soil samples representing high (TS), intermediate (SY) and low (LY/YC) levels of arsenic contamination were used in this study. The TS soil was collected in Tieshan District, a highly arsenic-contaminated region, which is located in Huangshi City, Hubei Province, central China.