The product of the ybdE gene of the Escherichia coli chromosome is involved in detoxification of silver ions

Transcription of the ykcZ-ylcA ylcBCD-ykdE region of the Escherichia coli K38 chromosome was analysed by Northern RNA-DNA hybridization, RT-PCR and primer extension. Transcription of a dicistronic ykcZ-ylcA mRNA and a tetracistronic ylcBCD-ybdE mRNA was induced by silver and was initiated from the sigma-70 promoters ylcAp and ylcBp. Expression of beta -galactosidase activity from a Phi (ylcBp-lacZ) operon fusion was also induced by Ag+ and Cu2+, but not by Zn2+. In-frame deletion of ybdE from the chromosome yielded a silver-sensitive E. coli mutant strain which did not differ in its copper resistance from its wild-type strain. On the of her hand, deletion of the copA gene for the copper-exporting P-type ATPase CopA resulted in copper sensitivity, but not in silver sensitivity. A Delta ybdE Delta copA double mutant strain behaved towards copper as the Delta copA strain and towards silver as the Delta ykdE strain. Thus, in E. coli, the YlcBCD-YbdE system may be involved in silver- but not in copper resistance, and CopA may be involved in copper- but not in silver resistance.