DEGRADATION OF PYRIDINE DERIVATIVES BY SOIL MICROORGANISMS (MICROCOCCUS, NOCARDIA)

Studies were conducted to evaluate microbial degradation of pyridine and pyridine derivatives in cultures and in soils. Two organisms were isolated from soil by enrichment with pyridine. The organisms, identified as Micrococcus luteus and a Nocardia spp., could not grow on or degrade mono- or disubstituted pyridinecarboxylic acids, hydroxy-, chloro-, amino-, or methylpyridines. Micrococcus luteus had pyridine-induced succinate semialdehyde dehydrogenase, as well as constitutive amidase activities, and degraded formate or formamide without a lag. The data indicate the organism degrades pyridine by C2-C3 ring cleavage without initial hydroxylation. Cells of M. luteus were permeable to pyridinecarboxylic acids, mono-hydroxypyridines, 2,3-dihydroxypyridine, mono-amino- and methylpyridines, indicating that permeability barriers did not account for extreme substrate specificity of the organism. Relationships between structure and biodegradability for pyridine derivatives were studied using soil and mixed cultures and measuring disappearance of the pyridine added as well as ammonium released from the pyridine ring. In nutrient solutions, pyridinecarboxylic acids, mono-hydroxypyridines, and the unsubstituted pyridine ring were all degraded within 24 days, and most within 7 days. Methylpyridines were intermediate in degradability, disappearing in \u3c7 to \u3e30 days. None of the aminopyridines was completely degraded in 30 days. Of the chloropyridines tested, only 4-chloropyridine was completely degraded in 24 days. During a 64 day incubation in soil, extractability of pyridine derivatives with KCl + HCl decreased from an average of 88% to essentially zero for all compounds except aminopyridines. From 36 to 94% of added aminopyridines was recovered after 64 days of incubation. Degradation of most pyridine derivatives was confirmed by accumulation of N in amounts equivalent to 61 to 80% of the decrease in extractable pyridines. Nitrogen did not accumulate in soil treated with 2,3-dihydroxypyridine, 2-, 3-, 2,3-, or 2,6-chloropyridines, suggesting that these compounds were not degraded. Lack of degradation for the latter 4 compounds was confirmed by 89 to 94% recovery during extraction of soil with methanol. For both nutrient solutions and soils, degradability of the compounds generally followed the order pyridinecarboxylic acids \u3e pyridine = mono-hydroxypyridines \u3e methylpyridines \u3e aminopyridines = chloropyridines