Effect of Nitrogen Source on End Products of Naphthalene Degradation

Abstract

Soil cultures, enrichment cultures, and pure culture isolates produced substantial quantities of salicylic acid from naphthalene in a mineral salts medium containing NH 4 Cl as the nitrogen source. However, when KNO 3 was substituted for NH 4 Cl, these same cultures failed to accumulate detectable quantities of salicylic acid but did turn the medium yellow. When an isolate identified as a Pseudomonas species was used, viable cell numbers were much greater in the medium containing KNO 3 , but up to 94% of the naphthalene was utilized in both media. After 48 h of incubation in a 0.1% naphthalene-mineral salts medium, the cultures containing NH 4 Cl showed irregular clumped cells, a pH of 4.7, 42 μg of salicylic acid per ml, and the production of 4.4 ml of CO 2 . Under the same conditions, the cultures in the medium containing KNO 3 showed uniform cellular morphology, a pH of 7.3, no salicylic acid, the production of 29.7 ml of CO 2 , and a distinct yellow coloration of the medium. The differences between nitrogen sources could not be accounted for by pH alone since results obtained using buffered media were similar. Growth with NH 4 NO 3 displayed a pattern similar to that obtained when NH 4 Cl was used. The yellow coloration in the medium containing KNO 3 was apparently due to more than one compound, none of which were 1,2-naphthoquinone or acidic in nature, as suggested by other investigators. Further attempts to identify the yellow compounds by high-pressure liquid chromatography, infrared analysis, and gas chromatography-mass spectrometry have been unsuccessful thus far.