Altered Mercury Transport in a Mutant of Pseudomonas fluorescens B69

Summary: A 34 MDal plasmid harboured by Pseudomonas fluorescens B69 carried a gene coding for the mercuric reductase enzyme, thus promoting mercury resistance in the host strain. Mercury-sensitive variants were isolated when a hypersensitive, cured derivative of strain B69 was exposed to 10 μg mercury (II) ml−1. The alteration in mercury transport appeared to be the result of a mutation, since a transconjugant of the mutant, which carried the mercury-resistance plasmid, showed a reduced rate of mercury volatilization compared to the parental resistant strain. In addition, more mercury was tightly bound to the mutant cells. This phenomenon represents a new aspect of bacterial resistance to mercurials.