A new pathway for isonicotinate degradation by Mycobacterium sp. INA1

An organism able to utilize isonicotinate aerobically as the sole source of carbon, nitrogen and energy was isolated from soil samples and identified as a Mycobacterium sp. No growth occurred on any other heteroaromatic substrate tested, except 2-hydroxyisonicotinate, which was shown to be an intermediate in isonicotinate metabolism. Degradation of isonicotinate involved two consecutive hydroxylations leading to 2,6-dihydroxy-isonicotinate (citrazinate). The reactions were catalysed by two different dehydrogenases, which were apparently molybdenum-dependent. Citrazinate was activated by CoA via a synthetase reaction, and the resulting citrazyl-CoA ester was reduced by a NADPH-dependent reductase. In the presence of 1 mm-arsenite, cells accumulated 2-oxoglutarate during isonicotinate metabolism.