Degradation of alkylpyridines by pseudonocardia sp. M43 and gordonia nitida LE31

Abstract

Alkylpyridines are toxic environmental pollutants commonly found in many surface- and groundwater near industries for the production of synthetic liquid fuels. In this study, alkylpyridines degrading bacteria were isolated from an industrial wastewater by enrichment culture technique and their taxonomic and degradation characteristics were investigated. One of the isolates, strain M43 degraded 4-methylpyridine (4-MP) and 4-ethylpyridine (4-EP) aerobically. Morphology, cellular fatty acid composition and sequence analysis of the 16s rDNA indicate that the bacterium is a member of the genus Pseudonocardia. The highest binary sequence similarity of 99.1 % was found with Pseudonocardia sulfidoxydans. The strain M43 was a filamentous bacterium and grew as pellicles in the liquid culture. During the course of 4-MP and 4-EP degradation, UV absorbing metabolites were transiently accumulated in the culture media. The metabolites produced from both 4-MP and 4-EP showed UV absorption maxima at 224 and 289 nm that are characteristic of 2-hydroxylated pyridines. The metabolite from 4-methylpyridine was identified to be 2-hydroxy-4-methylpyridine by mass spectral analysis. The strain M43 was able to use 2-hydroxy-4-methylpyridine as growth substrate. The results indicate that Pseudonocardia sp. strain M43 degraded 4-MP and 4-EP via initial hydroxylation to 2-hydroxy-4-methylpyridine and 2-hydroxy-4-ethylpyridine respectively. Beside of 4-MP and 4-EP, M43 also degraded pyridine among various pyridine derivatives. However, inability of M43 to use hydroxypyridines suggests that pyridine degradation pathway of M43 maybe different from the 4-MP and 4-EP degradation pathway. This is the first report on the hydroxylated intermediates produced during the degradation of 4-MP and 4-EP by pure culture. Another isolate, strain LE31 degraded 3-ethylpyridine and 3-methylpyridine The strain LE31 was taxonomically studied by polyphasic approach. Strain LE31 was identified as a member of the...