New clusters of arsenite oxidase and unusual bacterial groups in enrichments from arsenic-contaminated soil.

In the present study cultivation-dependent and molecular methods were applied in combination to investigate the arsenite-oxidizing communities in enrichment cultures from arsenic and lead smelter-impacted soils with respect to both 16S rRNA and arsenite oxidase gene diversity. Enrichments with arsenite as the only electron donor resulted in completely different communities than enrichments with yeast extract and the simultaneous presence of arsenite. The lithoautotrophic community appeared to be dominated by Ferrimicrobium-related Actinobacteria, unusual Acidobacteria, Myxobacteria, and α-Proteobacteria but the heterotrophic community comprised many Dokdonella-related γ-Proteobacteria. Gene sequences of clones encoding arsenite oxidase from the enrichment for lithoautotrophs belonged to three major clusters with sequences from non-cultivated microorganisms. So, primers used to detect arsenite oxidase genes could amplify the genes from many α-, β- and γ-Proteobacteria, but not from various strains of the other phyla present in the enrichment for lithotrophs. This was also observed for the isolates where arsenite oxidase genes from new proteobacterial isolates of the genera Burkholderia, Bosea, Alcaligenes, Bradyrhizobium and Methylobacterium could be amplified but the genes of the new Rhodococcus isolate S43 could not. The results indicate that the ability to oxidize arsenite is widespread in various unusual taxa, and molecular methods for their detection require further improvement.