Abstract
So far, numerous genes have been found to associate with various strategies to resist and transform the toxic metalloid arsenic (here, we denote these genes as “arsenic-related genes”). However, our knowledge of the distribution, redundancies and organization of these genes in bacteria is still limited. In this study, we analyzed the 188 Burkholderiales genomes and found that 95% genomes harbored arsenic-related genes, with an average of 6.6 genes per genome. The results indicated: a) compared to a low frequency of distribution for aio (arsenite oxidase) (12 strains), arr (arsenate respiratory reductase) (1 strain) and arsM (arsenite methytransferase)-like genes (4 strains), the ars (arsenic resistance system)-like genes were identified in 174 strains including 1,051 genes; b) 2/3 ars-like genes were clustered as ars operon and displayed a high diversity of gene organizations (68 forms) which may suggest the rapid movement and evolution for ars-like genes in bacterial genomes; c) the arsenite efflux system was dominant with ACR3 form rather than ArsB in Burkholderiales; d) only a few numbers of arsM and arrAB are found indicating neither As III biomethylation nor AsV respiration is the primary mechanism in Burkholderiales members; (e) the aio-like gene is mostly flanked with ars-like genes and phosphate transport system, implying the close functional relatedness between arsenic and phosphorus metabolisms. On average, the number of arsenic-related genes per genome of strains isolated from arsenic-rich environments is more than four times higher than the strains from other environments. Compared with human, plant and animal pathogens, the environmental strains possess a larger average number of arsenic-related genes, which indicates that habitat is likely a key driver for bacterial arsenic resistance.
Highlights
Arsenic (As) is considered one of the most toxic metalloids widely distributed on earth
NO1, Alcaligenes faecalis subsp. faecalis NCIB 8687, Herminiimonas arsenicoxydans ULPAs1 and Thiomonas sp. 3As were the sequenced arsenite oxidizers isolated from niches contaminated with arsenic, in which, the mechanisms related to arsenic resistance and arsenite oxidation have been widespread investigated [16,17,18,19,28,29,30,31,32,33]
Many studies have revealed the widespread distribution of arsenic-related genes in bacteria, and arsenic-related genes have been isolated from a large number of bacteria from different niches [1,4,8,9,11,13,41]
Summary
Arsenic (As) is considered one of the most toxic metalloids widely distributed on earth. To adapt to habitats contaminated with arsenic, microbes have developed multiple strategies for resistance to and transformation of arsenic These strategies have primarily included the following: 1) cytoplasmic/ periplasmic AsV reduction and As III extrusion; 2) As III oxidation and AsV extrusion; and 3) As III methylation and volatilization by way of the formation of a gas, called biomethylation [2,3,4,5,6].
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