The heavy metal tolerant soil bacterium Achromobacter sp. strain AO22 encodes acop locus and its copper biosensor ability
2011
Ng, Shee Ping | Palombo, Enzo A. | Bhave, Mrina
Copper-containing compounds are introduced into the environment through agricultural products, mining and metal industries, and cause severe detrimental effects on ecosystems. Certain microorganisms exposed to these stressors appear to have developed mechanisms to maintain intracellular copper homeostasis and avoid toxicity. This study aimed to identify the copper homeostasis determinants from a multi-metal tolerant soil bacterium, Achromobacter sp. A022. A cluster of genes, designated copSRABGOFCDK, was identified, of which copSRAB and copCD are related to the cop operons of Pseudomonas syringae and Cupriavidus metallidurans CH34 and pco of E. coli, which encode systems that sequester in or export excess copper from the periplasm. copF encodes a putative heavy metal P-type ATPase with a role of cytoplasmic copper efflux, while copG, copO and copK encode putative periplasmic copper chaperones. Sequencing of the flanking regions of the A022 cop locus indicated that it could be present on a genomic island (GI). A section of DNA between copR and copA was functionally identified as a copper responsive promoter using a lacZ reporter construct, pCOPRP, in E. coli. In an engineered strain of A022 carrying the same plasmid, designated A022 (pCOPRP), expression of lacZ was enhanced 140-fold in the presence of Cu but minimal when exposed to cadmium, lead, mercury. silver, and zinc. This soil bacterium and its cop operon thus make excellent systems for studying copper homeostasis and designing biosensors for environmental copper contamination, rather than the enteric E. coli.
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