Isolation, Identification, and Characterization of a Lipoate-Degrading Pseudomonad and of a Lipoate Catabolite

Abstract

A strain of bacteria that can degrade lipoic acid was isolated from soil. The bacterium, adapted to use 0.4% dl -lipoate as the sole organic substrate to supply carbon, sulfur, and energy, was identified morphologically and physiologically as a strain of Pseudomonas putida . Degradation of 1,6 - 14 C -lipoic acid, synthesized from 1,6 - 14 C -adipic acid, was evidenced by: (i) loss of approximately 50% of the total radioactivity from the medium after bacterial growth; (ii) appearance of 14 C-degradation products upon paper and thin-layer chromatography of the culture medium; and (iii) oxygraphically measured utilization of O 2 by cells in the presence of lipoate or other oxidizable substrates. Analyses of the benzene extract of culture medium by infrared, nuclear magnetic resonance, and mass spectrometry, and by gas-liquid chromatography after desulfuration, have characterized bisnorlipoic acid, or 4,6-dithiohexanoic acid, as the major catabolite present in the medium. β-Oxidation of the side chain is thus proven to be a pathway employed by the pseudomonad to degrade lipoic acid.