Microbiological transformation of pyridine N-oxide and pyridine by Nocardia sp.

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Abstract
A Nocardia sp., which utilises pyridine N-oxide (PNO), 2-hydroxypyridine, and pyridine as sole sources of carbon, nitrogen, and energy, has been isolated from soil by enrichment on PNO. PNO-adapted cells rapidly oxidized PNO and 2-hydroxypyridine; pyridine was oxidized very slowly. 2-Hydroxy pyridine- and pyridine-adapted cells oxidized their respective substrates, but PNO was not oxidized. Dihydroxypyridines did not accumulate during growth of the organism, but the formation of blue pigments during fermentation of PNO and 2-hydroxypyridine suggested their transient participation. The pigment has been characterized as 4,5,4′,5′-tetrahydroxy-3,3′-diazadiphenoquinone-(2,2′). No pigment was formed during pyridine metabolism. 2,5-Dihydroxypyridine was oxidized by PNO- and 2-hydroxypyridine-adapted but not by pyridine-adapted cells. Succinic semialdehyde was characterized as the intermediate of pyridine metabolism from semicarbazide-inhibited cultures; it was rapidly oxidized by pyridine-adapted cells. Pyridine N-oxide is therefore metabolized in this Nocardia sp. via 2-hydroxypyridine and 2,5-dihydroxypyridine, but these compounds do not serve as intermediates of pyridine metabolism.