Characterization of pyridine degrading bacteria isolated from oil shale column

Abstract

From the anoxic zone of an oil shale leachate column three pyridine-degrading bacterial strains were isolated. Two strains were Gramnegative facultatively anaerobic rods and one strain was a branched Grampositive bacterium. The branched Gram-positive strain had the best pyridine-degrading ability. This organism was aerobic, non-motile, catalase positive, oxidase negative, and had no flagellum. The G+C content of the DNA was 66.5 mol\%. The major menaquinone was MK-8($H_2$). The main cellular fatty acids were saturated and monounsaturated straight chains. This organism contained mycolic acid, meso-diaminopimelic acid, arabinogalactan and glycolyl residues in the cell wall. Due to morphological, physiological and chemotaxonomic characteristics this strain was placed in the genus Rhodococcus. The optimum culture conditions were as follows: temperature 30-32$^\circ$C, pH 7.0-8.0 and 0.1\% v/V of pyridine as sole carbon, energy and nitrogen source. Utilization of pyridine by a batch fermentor culture of Rhodococcus sp. was characterized by a specific growth rate of 0.12 $h^{-1}$, specific oxygen uptake rate of 9.76 $mMO_2$/g.hour, growth yield of 0.34 me cell mg pyridine$^{-1}$ and a doubling time of $5.3^{-1}$. The system for the metabolism of pyridine by Rhodococcus sp. is constitutive and specific for pyridine. This organism could be grow on many other toxic aromatic compounds as the sole carbon source.