MECHANISM INVOLVED IN THE METABOLISM OF NITROPHENYL-CARBOXYLIC ACID COMPOUNDS BY MICROORGANISMS

Abstract

The stepwise reduction of nitrate has been studied rather extensively during the past years and metabolic schemes have been postulated from the data obtained from growth, inhibition, and respiration experiments. The reduction of nitrate to nitrite is generally accepted although the pathway below nitrite is still rather poorly defined. Hydroxylamine has long been postulated as an intermediate in the scheme of reduction of nitrite to ammonia and this proposal has received support from a number of workers. Taniguchi and co-workers (1953) demonstrated that cell-free extracts of Bacillus pumilis reduced nitrate, nitrite, and hydroxylamine to ammonia when reduced methylene blue was present as an elec-tron donor. Silver and McElroy (1954) have postulated a tentative scheme for nitrate reduc-tion in Neurospora crassa and discussed the possi-bility that free hydroxylamine existed as an intermediate in the pathway of nitrite reduction. These workers also carried out experiments designed to study the reduction of m-dinitro-benzene in support of the postulation that ni-trate metabolism might involve incorporating the inorganic nitrogen into an organic molecule before reduction to the amino level as proposed by de la Haba (1950). Related studies have shown that certain nitrogen containing carbox-ylic acid compounds may readily be metabolized by microorganisms (Durham, 1958). In an attempt to clarify some of the questions that have been raised concerning hydroxplamine as an intermediate in nitrate and nitrite assimila-tion we have undertaken studies involving the metabolism of nitrophenyl-carboxylic acid com-