Bacillus sp. CDB3 isolated from cattle dip-sites possesses two ars gene clusters
Somanath Bhat , Xi Luo , Zhiqiang Xu , Lixia Liu , Ren Zhang
DOI:
Received January 29, 2010,Revised August 31, 2010, Accepted , Available online
Volume 23,2011,Pages 95-101
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Contamination of soil and water by arsenic is a global problem. In Australia, the dipping of cattle in arsenic-containing solution
to control cattle ticks in last centenary has left many sites heavily contaminated with arsenic and other toxicants. We had previously
isolated five soil bacterial strains (CDB1-5) highly resistant to arsenic. To understand the resistance mechanism, molecular studies have
been carried out. Two chromosome-encoded arsenic resistance (ars) gene clusters have been cloned from CDB3 (Bacillus sp.). They
both function in Escherichia coli and cluster 1 exerts a much higher resistance to the toxic metalloid. Cluster 2 is smaller possessing
four open reading frames (ORFs) arsRorf2BC, similar to that identified in Bacillus subtilis Skin element. Among the eight ORFs in
cluster 1 five are analogs of common ars genes found in other bacteria, however, organized in a unique order arsRBCDA instead of
arsRDABC. Three other putative genes are located directly downstream and designated as arsTIP based on the homologies of their
theoretical translation sequences respectively to thioredoxin reductases, iron-sulphur cluster proteins and protein phosphatases. The
latter two are novel of any known ars operons. The arsD gene from Bacillus species was cloned for the first time and the predict protein
di ers from the well studied E. coli ArsD by lacking two pairs of C-terminal cysteine residues. Its functional involvement in arsenic
resistance has been confirmed by a deletion experiment. There exists also an inverted repeat in the intergenic region between arsC and
arsD implying some unknown transcription regulation.
