Detection of catabolic genes in indigenous microbial consortia isolated from a diesel-contaminated soil

Bioremediation is often used for in situ remediation of petroleum-contamina ted sites. The primary focus of this study was on understanding the indigen ous microbial community which can survive in contaminated environment and i s responsible for the degradation. Diesel, toluene and naphthalene-degradin g microbial consortia were isolated from diesel-contaminated soil by growin g on selective hydrocarbon substrates. The presence and frequency of the ca tabolic genes responsible for aromatic hydrocarbon biodegradation (xylE, nd oB) within the isolated consortia were screened using polymerase chain reac tion PCR and DNA-DNA colony hybridization. The diesel DNA-extract possessed both the xylE catabolic gene for toluene, and the nah catabolic gene for p olynuclear aromatic hydrocarbon degradation. The toluene DNA-extract posses sed only the xylE catabolic gene, while the naphthalene DNA-extract only th e ndoB gene. Restriction enzyme analysis with HaeIII indicated similar rest riction patterns for the xylE gene fragment between toluene DNA-extract and a type strain, Pseudomonas putida ATCC 23973. A substantial proportion (74 %) of the colonies from the diesel-consortium possessed the xylE gene, and the ndoB gene (78%), while a minority (29%) of the toluene-consortium harbo red the xylE gene. 59% of the colonies from the naphthalene-consortium had the ndoB gene, and did not have the xylE gene. These results indicate that the microbial population has been naturally enriched in organisms carrying genes for aromatic hydrocarbon degradation and that significant aromatic bi odegradative potential exists I the site. Characterization of the populatio n genotype constitutes a molecular diagnosis which permits the determinatio n of the catabolic potential of the site to degrade the contaminant present . (C) 2001 Elsevier Science Ltd. All rights reserved.