CROSS HYBRIDIZATION OF PLASMID AND GENOMIC DNA FROM AROMATIC AND POLYCYCLIC AROMATIC HYDROCARBON DEGRADING BACTERIA

Forty-three bacterial strains were collected from various environmental and commercial sources and their ability to degrade polycyclic aromatic hydrocarbons (PAHs) was confirmed using the criteria of growth, mineralization, and oxidation. Undigested genomic DNA from these strains was blotted by Southern transfer to replicate membranes, which were probed either with purified plasmids (e.g., TOL and NAH7, associated with toluene and naphthalene degradation, respectively) or with genomic DNA from the other strains. The isolates were grouped according to hybridization and PAH-degradation results. One group of eight strains grew on naphthalene vapors as sole carbon source and hybridized with archetypical NAH plasmids. Another group of six isolates mineralized phenanthrene but could not grow on naphthalene, and their cryptic plasmids hybridized with Pseudomonas sp. HL7b, which degrades a wide range of PAHs. The remaining isolates, which could not grow on naphthalene but mineralized and (or) oxidized a variety of PAHs, hybridized with neither the pure plasmids nor heterologous genomic DNA, implying that their PAH-degradative genes were significantly dissimilar. This suggests that using TOL or NAH plasmids to probe an environmental population might reveal toluene- or naphthalene-degradative genes but would underestimate the occurrence of PAH-degradative genes. We suggest that a suite of probes would be necessary to evaluate the PAH-degradation potential of a mixed population.