Activities And Related Genes Of Arsenite Oxidizers Inhabiting Arsenic-Contaminated Soil And Sediment

Nowadays, arsenic contamination has become a global concern. Over 10 million population from more than 20 provinces in China suffer from arsenic toxicity. Natural processes as well as anthropogenic activities lead arsenic from earth’s crust to be released into the environment. Jianghan Plain is a natural-occurred arsenic contaminated area, and Hunam Shimen is heavily contaminated by local realgar mining processes. This study selected Jianghan Plain and Hunan Shimen as sampling locations, and collected 6 soil and sediment samples to investigate the arsenic oxidizers inhabiting there. Microbial arsenite oxidation was explored on the community level and the molecular mechanisms under the bacteria-mediated transformation of arsenic was studied. This study also cloned the aio gene clusters from a typical highly efficient arsenite oxidizer, and explored the factors that regulate this strain’s ability to oxidize arsenite.According to the results, arsenic oxidizers inhabit both two sampling locations can oxidize considerable amount of arsenite to arsenate completely. The microbial community in Hunam Shimen can rapidly oxidize arsenite up to 5mM, and the ones from Jianghan Plain can oxidize 1 mM arsenite in a manner of days. These results suggest that various microbial trophic groups distributed widely in both natural occurred and people-made arsenic-contaminated areas, and a great number of them possess the ability to oxidize arsenite.Additionally,19 arsenite oxidizers were isolated from Mesorhizobium, Rhizobium, Pseudoxanthomonas, Achromobacter, Ensifer, Sphingopyxis, Flavobacterium, Pusillimonas, Shinella, Arthrobacter, Pseudomonas and Aminobacter,15 of which can oxidize 1mM to 5mM arsenite to arsenate in 2-5 days. Through molecular approaches, aio genes were cloned from 8 arsenite oxidizers and the mechanisms under the microbial arsenite oxidation were analyzed.Moreover, the aio gene clusters was cloned from a highly efficient arsenite oxidizer, designated Mesorhizobium sp. AOA-1. The structure of the aio gene clusters is aioB-aioA-cycC-moeA, and the highest identities of these four genes with corresponding genes identified from known arsenite oxidizers are 95%,79%,66% and 75%, respectively. Results also shown that higher concentration of arsenite can induce higher level of aio gene expressions in Mesorhizobium sp. AOA-1, and thereby enhance its ability to oxidize arsenite. Environmental factors also play roles in the regulation of microbial arsenite oxidation. Fe3+, NO3-, and SO42- moderately inhibit arsenite oxidation in Mesorhizobium sp. AOA-1, and Mn2+ significantly inhibits its ability to oxidize arsenite, while PO43- evidently enhances the arsenite oxidation process.This study has systematically investigated the microbial communities inhabiting different arenic-contaminated areas, isolated a number of arsenite oxidizers, and explored the mechanisms under the arsenic transformation processes. We have also cloned aio gene clusters from a highly efficient arsenic oxidizer and studied the factors that regulate its arsenite-oxidizing ability. Our results gained insights into the theoretical basis for microbial mediated arsenic-cycling, and provided potential materials to construct efficient arsenic-removal systems.