Expression of chromate resistance genes from Shewanella sp. strain ANA-3 in Escherichia coli.

The plasmidic chromate resistance genes chrBAC from Shewanella sp. strain ANA-3 were transferred to Escherichia coli. Expression of chrA alone, on a high- or low-copy number plasmid, conferred increased chromate resistance. In contrast, expression of the complete operon chrBAC on a high-copy number plasmid did not result in a significant increase in resistance, although expression on a low-copy number plasmid made the cells up to 10-fold more resistant to chromate. The chrA gene also conferred increased chromate resistance when expressed in Pseudomonas aeruginosa. The chrR gene from the P. aeruginosa chromosome was necessary for full chromate resistance conferred by chrA. A diminished chromate uptake in cells expressing the chrA gene suggests that chromate resistance is due to chromate efflux.