Naphthalene degradation is an excellent model system for studying the relationship of bacterial function, naphthalene degradation, to bacterial community structure and gene exchange in the environment. Naphthalene-degrading bacteria are taxonomically diverse and the catabolic pathways for naphthalene are often encoded on plasmids. In a preliminary experiment, the initial genes of the Pseudomonas putida pathway for naphthalene degradation, nahAB, were used to probe the DNA of naphthalene degrading bacteria isolated from sediments and soils. Most of the soil isolates, about 50% of the freshwater isolates, but only 10% of the estuarine isolates displayed homology with the nahAB probe under highly stringent conditions for hybridization. The results indicate that gene exchange among naphthalene-degraders may be habitat-specific. The objectives of the proposed investigation are to collect and classify naphthalene-degrading bacteria from diverse environments, to determine the extent of homology between nahAB and the DNA of the degraders, and to analyze the relationship among nahAB homology, phenotypic- relatedness of the naphthalene degraders, and habitat distribution. First, a large collection of naphthalene degraders will be established by using a relatively nonselective isolation technique and by obtaining strains from existing cultures. Naphthalene-degraders will be classified by a numerical taxonomy approach. Degraders will be screened for plasmids and their degree of homology with the nahAB DNA probe will be determined by a semi-quantitative slot blot method. Field and laboratory data will be coded, stored in a mainframe computer, and analyzed for possible relationships by multivariate statistical methods. The study will yield baseline information on the ecology of naphthalene degraders and the extent of genetic exchange among bacteria of biogeochemical importance in the natural environment.
