Abstract

The chromium resistance properties encoded by a natural plasmid recovered from the environment were investigated. A 200 kb plasmid was isolated by the exogenous plasmid isolation method. The plasmid conferred a chromate resistance phenotype (MIC 8 mmol l -1) to a chromate susceptible strain of Pseudomonas putida KT 2441 (MIC 0.5 mmol l -1). The resistant strain took up 50% less 51Cr than the isogenic susceptible strain of Ps. putida KT2441. In addition, the resistant strain expressed two new membrane proteins encoded by the plasmid, an outer membrane protein (molecular weight 60 000) and an inner membrane protein (molecular weight 35 000). The physiological significance of these proteins is under current investigation.