Abstract
BackgroundArsenic (As) is a natural metalloid, widely used in anthropogenic activities, that can exist in different oxidation states. Throughout the world, there are several environments contaminated with high amounts of arsenic where many organisms can survive. The most stable arsenical species are arsenate and arsenite that can be subject to chemically and microbiologically oxidation, reduction and methylation reactions. Organisms surviving in arsenic contaminated environments can have a diversity of mechanisms to resist to the harmful effects of arsenical compounds.ResultsThe highly metal resistant Ochrobactrum tritici SCII24 was able to grow in media with arsenite (50 mM), arsenate (up to 200 mM) and antimonite (10 mM). This strain contains two arsenic and antimony resistance operons (ars1 and ars2), which were cloned and sequenced. Sequence analysis indicated that ars1 operon contains five genes encoding the following proteins: ArsR, ArsD, ArsA, CBS-domain-containing protein and ArsB. The ars2 operon is composed of six genes that encode two other ArsR, two ArsC (belonging to different families of arsenate reductases), one ACR3 and one ArsH-like protein. The involvement of ars operons in arsenic resistance was confirmed by cloning both of them in an Escherichia coli ars-mutant. The ars1 operon conferred resistance to arsenite and antimonite on E. coli cells, whereas the ars2 operon was also responsible for resistance to arsenite and arsenate. Although arsH was not required for arsenate resistance, this gene seems to be important to confer high levels of arsenite resistance. None of ars1 genes were detected in the other type strains of genus Ochrobactrum, but sequences homologous with ars2 operon were identified in some strains.ConclusionA new strategy for bacterial arsenic resistance is described in this work. Two operons involved in arsenic resistance, one giving resistance to arsenite and antimonite and the other giving resistance to arsenate were found in the same bacterial strain.
Highlights
Arsenic (As) is a natural metalloid, widely used in anthropogenic activities, that can exist in different oxidation states
Most ars operons consist of three genes: arsR, arsB and arsC, and most of the knowledge about these genes comes from studies of ars operons in Escherichia coli [3], Pseudomonas aeruginosa [4] and Staphylococcus species [5,6]
Arsenic resistance of Ochrobactrum tritici SCII24T Tolerance to arsenite, arsenate and antimonite were tested in O. tritici SCII24
Summary
Arsenic (As) is a natural metalloid, widely used in anthropogenic activities, that can exist in different oxidation states. Organisms surviving in arsenic contaminated environments can have a diversity of mechanisms to resist to the harmful effects of arsenical compounds. The second family of arsenite carriers has been much less characterized and includes the arsB gene of Bacillus subtilis [17] and the Acr gene from Saccharomyces cerevisiae [18]. Another gene, arsH, without a clear function described, has been found close to arsenic resistance genes in Yersinia enterocolitica [19], in Acidothiobacillus ferroxidans [20], in Serratia marcescens [21], in Synechocystis sp. In addition to the above mentioned arsenic resistance operons, a broad diversity of ars operons have been described in different species [26,27,28,29,30,31]
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