Genes involved in arsenic transformation and resistance associated with different levels of arsenic-contaminated soils

Abstract

BackgroundArsenic is known as a toxic metalloid, which primarily exists in inorganic form [As(III) and As(V)] and can be transformed by microbial redox processes in the natural environment. As(III) is much more toxic and mobile than As(V), hence microbial arsenic redox transformation has a major impact on arsenic toxicity and mobility which can greatly influence the human health. Our main purpose was to investigate the distribution and diversity of microbial arsenite-resistant species in three different arsenic-contaminated soils, and further study the As(III) resistance levels and related functional genes of these species.ResultsA total of 58 arsenite-resistant bacteria were identified from soils with three different arsenic-contaminated levels. Highly arsenite-resistant bacteria (MIC > 20 mM) were only isolated from the highly arsenic-contaminated site and belonged to Acinetobacter, Agrobacterium, Arthrobacter, Comamonas, Rhodococcus, Stenotrophomonas and Pseudomonas. Five arsenite-oxidizing bacteria that belonged to Achromobacter, Agrobacterium and Pseudomonas were identified and displayed a higher average arsenite resistance level than the non-arsenite oxidizers. 5 aoxB genes encoding arsenite oxidase and 51 arsenite transporter genes [18 arsB, 12 ACR3(1) and 21 ACR3(2)] were successfully amplified from these strains using PCR with degenerate primers. The aoxB genes were specific for the arsenite-oxidizing bacteria. Strains containing both an arsenite oxidase gene (aoxB) and an arsenite transporter gene (ACR3 or arsB) displayed a higher average arsenite resistance level than those possessing an arsenite transporter gene only. Horizontal transfer of ACR3(2) and arsB appeared to have occurred in strains that were primarily isolated from the highly arsenic-contaminated soil.ConclusionSoils with long-term arsenic contamination may result in the evolution of highly diverse arsenite-resistant bacteria and such diversity was probably caused in part by horizontal gene transfer events. Bacteria capable of both arsenite oxidation and arsenite efflux mechanisms had an elevated arsenite resistance level.

Metagenomic analysis revealed highly diverse microbial arsenic metabolism genes in paddy soils with low-arsenic contents

“…We used the m 8 output format and e-value cutoffs of 1e À5 to do the best BLAST search (Mackelprang et al, 2011). The BLASTX outputs against As metabolism protein database were screened by a self-written script to extract alignments of aligned length !25 aa and identity !90% (Cai et al, 2009). Based on data from BLAST research and script-screening, the proportions of different types of As metabolism genes were defined as "percentage" (%, in "total As metabolism genes sequences") and "abundance" (ppm, one read in one million reads, in "total metagenome sequences"), respectively .…”

Structural and functional genomics of plasmid pSinA of Sinorhizobium sp. M14 encoding genes for the arsenite oxidation and arsenic resistance

“…The same synteny, but only for five genes, aioSRABcytC, is also found in the arsenite oxidase module of Achromobacter sp. SY8 strain (Cai et al, 2009). Homologs of the aioSR (twocomponent signal-transduction system) and aioAB (arsenite oxidase) genes are also present in the aio/aox loci of Herminiimonas arsenicoxydans (Muller et al, 2007) and Alcaligenes faecalis (Silver and Phung 2005a), but the regulatory genes (aioSR/aoxSR) in these hosts are separated from the structural genes (aioAB) by an additional ORF.…”

Characterization and transcription of arsenic respiration and resistance genes during in situ uranium bioremediation

“…ArsB and Acr3 are unrelated families of arsenic transporters and homologs of each type are widespread throughout bacteria, archaea and fungi (Rosen, 1999;Mukhopadhyay et al, 2002). Although Acr3 is less well characterized, it is present in more phylogenetically distant species than ArsB (Rosen, 1999;Achour et al, 2007;Cai et al, 2009). On the basis of the phylogenetic dissimilarities, Acr3 members can be divided in two subfamilies, Acr3(1) and Acr3(2) (Rosen, 1999;Wysocki et al, 2003;Achour et al, 2007).…”

“…On the basis of the phylogenetic dissimilarities, Acr3 members can be divided in two subfamilies, Acr3(1) and Acr3(2) (Rosen, 1999;Wysocki et al, 2003;Achour et al, 2007). The presence of arsenic resistance genes can serve as biomarkers of arsenic contamination in environmental samples (Anderson and Cook, 2004;Ford et al, 2005;Jackson et al, 2005;Cai et al, 2009).…”