Selection of clc, cba, and fcb chlorobenzoate-catabolic genotypes from groundwater and surface waters adjacent to the Hyde Park, Niagara Falls, chemical landfill

The frequency of isolation of three nonhomologous chlorobenzoate catabolic genotypes (clc, cba, and fcb) was determined for 464 isolates from freshwat er sediments and ground-water in the vicinity of the Hyde Park industrial l andfill site in the Niagara watershed. Samples were collected from both con taminated and noncontaminated sites during spring, summer, and fall and enr iched at 4, 22, or 32 degrees C with micromolar to millimolar concentration s of chlorobenzoates and 3-chlorobiphenyl (M. C. Peel and R. C. Wyndham, Mi crob, Ecol: 33:59-68, 1997). Hybridization at moderate stringency to restri ction-digested genomic DNA with DNA probes revealed the chlorocatechol 1,2- dioxygenase operon (clcABD), the 3-chlorobenzoate 3,4-(4,5)-dioxygenase ope ron (cbaABC, and the 4-chlorobenzoate dehalogenase (fcbB) gene in isolates enriched from all contaminated sites in the vicinity of the industrial land fill. Nevertheless, the known genes were found in less than 10% of the isol ates from the contaminated sites, indicating a high level of genetic divers ity in the microbial community. The known genotypes were not enriched from the noncontaminated control sites nearby. The de, cba, and fcb isolates wer e distributed across five phenotypically distinct groups based on Biolog ca rbon source utilization, with the breadth of the host range decreasing in t he order clc > cba > feb. Restriction fragment length polymorphism (RFLP) p atterns showed that the cba genes were conserved in all isolates whereas th e clc and fcb genes exhibited variation in RFLP patterns. These observation s are consistent with the recent spread of the cba genes by horizontal tran sfer as part of transposon Tn5271 in response to contaminant exposure at Hy de Park. Consistent with this hypothesis, IS1071, the flanking element in T n5271, was found in all isolates that carried the cba genes. Interestingly, IS1071 was also found in a high proportion of isolates from Hyde Park carr ying the clc and fcb genes, as well as in type strains carrying the clcABD operon and the biphenyl (bph) catabolic genes.