Identification of Metal Resistance Genes in a Strain of Enterobacter cloacae

Abstract

A multi-metal resistant strain of Enterobacter cloacae (E. cloacae) grows when exposed to toxic salts of mercury, cadmium, zinc, copper and selenite. In general, bacteria respond to toxic metal concentrations using efflux mechanisms, metal transformation (reduction and oxidation), and sequestration. Transposon mutagenesis was used to generate five selenite sensitive, two zinc sensitive and three cadmium sensitive strains of E. cloacae. DNA sequencing of the mutagenized genes suggested that a polyphosphate kinase, a sporulation domain protein, a Lon protease and Type-II Secretion protein may be involved in selenite resistance. In addition, a P-type ATPase may be involved in Zn resistance. The sporulation domain protein, tyrosine recombinase and Lon protease may be expressed in response to selenite-induced oxidative stress, the polyphosphate kinase may be involved in selenite reduction and processing and the type-II Sec protein may be involved in selenite efflux. The P-type ATPase may be involved in mercury/cadmium/zinc efflux. Finally, the sequence of two cloned PCR fragments indicated that the E. cloacae strain contains genes for copper and mercury resistance. By studying metal-resistance mechanisms, it may be possible to develop strategies to clean metal-contaminated waste sites.