Anaerobic naphthalene degradation by microbial pure cultures under nitrate-reducing conditions

Pure bacterial cultures were isolated from a highly enriched denitrifying c onsortium previously shown to anaerobically biodegrade naphthalene. The iso lates were screened for the ability to grow anaerobically in liquid culture with naphthalene as the sole source of carbon and energy in the presence o f nitrate. Three naphthalene-degrading pure cultures were obtained, designa ted NAP-3-1, NAP-3-2, and NAP-4. Isolate NAP-3-1 tested positive for denitr ification using a standard denitrification assay. Neither isolate NAP-3-2 n or isolate NAP-4 produced gas in the assay, but both consumed nitrate and N AP-4 produced significant amounts of nitrite. Isolates NAP-4 and NAP-3-1 tr ansformed 70 to 90% of added naphthalene, and the transformation was nitrat e dependent, No significant removal of naphthalene occurred under nitrate-l imited conditions or in cell-free controls. Both cultures exhibited partial mineralization of naphthalene, representing 7 to 20% of the initial added C-14-labeled naphthalene. After 57 days of incubation, the largest fraction of the radiolabel in both cultures was recovered in the cell mass (30 to 5 0%), with minor amounts recovered as unknown soluble metabolites. Nitrate c onsumption, along with the results from the C-14 radiolabel study, are cons istent with the oxidation of naphthalene coupled to denitrification for NAP -3-1 and nitrate reduction to nitrite for NAP-4. Phylogenetic analyses base d on 16S ribosomal DNA sequences of NAP-3-1 showed that it,vas closely rela ted to Pseudomonas stutzeri and that NAP-4 was closely related to Vibrio pe lagius. This is the first report we know of that demonstrates nitrate-depen dent anaerobic degradation and mineralization of naphthalene by pure cultur es.