Detection of heavy metal ion resistance genes in Gram-positive and Gram-negative bacteria isolated from a lead-contaminated site

Resistance to a range of heavy metal ions wasdetermined for lead-resistant and other bacteria whichhad been isolated from a battery-manufacturing sitecontaminated with high concentrations of lead. Several Gram-positive (belonging to the genera Arthrobacter and Corynebacterium) andGram-negative (Alcaligenes species) isolateswere resistant to lead, mercury, cadmium, cobalt,zinc and copper, although the levels of resistance tothe different metal ions were specific for eachisolate. Polymerase chain reaction, DNA-DNAhybridization and DNA sequencing were used to explorethe nature of genetic systems responsible for themetal resistance in eight of the isolates. SpecificDNA sequences could be amplified from the genomic DNAof all the isolates using primers for sections of themer (mercury resistance determinant on thetransposon Tn501) and pco (copperresistance determinant on the plasmid pRJ1004) geneticsystems. Positive hybridizations with mer andpco probes indicated that the amplified segmentswere highly homologous to these genes. Some of thePCR products were cloned and partially sequenced, andthe regions sequenced were highly homologous to theappropriate regions of the mer and pcodeterminants. These results demonstrate the widedistribution of mercury and copper resistance genes inboth Gram-positive and Gram-negative isolates obtainedfrom this lead-contaminated soil. In contrast, theczc (cobalt, zinc and cadmium resistance) andchr (chromate resistance) genes could not beamplified from DNAs of some isolates, indicating thelimited contribution, if any, of these genetic systemsto the metal ion resistance of these isolates.