The bacterial oxidation of N-methylisonicotinate, a photolytic product of Paraquat

Abstract

Two bacteria have been isolated that are capable of oxidizing N-methylisonicotinate, a photodegradation product of Paraquat (1.1'-dimethyl-4,4'-bipyridylium ion). N-Methylisonicotinate-grown cells of strain 4C1, a Gram-positive rod, oxidized 2-hydroxy-N-methylisonicotinate without lag. Cell-free extracts of these cells converted 2-hydroxyisonicotinate into 2,6-dihydroxyisonicotinate; the reaction did not require molecular oxygen. Maleamate was deamidated and maleate isomerized to fumarate by soluble enzyme systems. [(14)C]Formaldehyde was isolated as the dimedone derivative from the supernatant of a cell suspension oxidizing N-[(14)C]methylisonicotinate, and no [(14)C]-methylamine was detected. Whole cells incubated with N-methyl[carboxy-(14)C]isonicotinate released 95% of the radioactivity as (14)CO(2). The second bacterium, strain 4C2, a Gram-negative rod, did not oxidize any of the mono- or di-hydroxypyridines or their N-methyl derivatives that were available or could be synthesized; nor did cell-free extracts oxidize any of these compounds. Methylamine was oxidized by whole cells without lag; cell-free extracts converted methylamine into formaldehyde when a soluble enzyme system requiring an electron acceptor was used; formaldehyde was oxidized to formate and formate to CO(2) by enzyme systems requiring NAD(+).

Biodegradation of Pyridine Derivatives in Soil Suspensions

“…The same result was reported by Naik et al [21]. Organisms capable of metabolizing the monoisomers have been isolated [8,9,11,13], and it appears that all three can be converted to diols and metabolized via the maleamate pathway. Picolinate (Zpyridinecarboxylic acid) is metabolized by Bacillus [26] and by a gram-negative rod [13] after hydroxylation first at position 6.…”

“…It appears that the unsubstituted ring is cleaved without initial hydroxylation . Isonicotinic acid (Cpyridinecarboxylic acid) may also be metabolized without initial hydroxylation, or it may be converted t o a dihydroxy derivative prior t o ring fission [8]. All monohydroxypyridines and monopyridinecarboxylic acids can be converted t o diols prior to ring fission .…”

Catabolism of isonicotinate by Mycobacterium sp. INA1: extended description of the pathway and purification of the molybdoenzyme isonicotinate dehydrogenase

“…INA1, these facts do not necessarily contradict an involvement of citrazinate as a true intermediate (Kretzer & Andreesen, 1991). 2-Hydroxyisonicotinate and citrazinate were finally also shown to be intermediates in N-methylisonicotinate metabolism by the unidentified Gram-positive strain 4C 1 (Orpin et al, 1972). A further intermediate was maleamate.…”

Microbial metabolism of the pyridine ring. The hydroxylation of 4-hydroxypyridine to pyridine-3,4-diol (3,4-dihydroxypyridine) by 4-hydroxypyridine 3-hydroxylase

“…During a study of the microbial metabolism of the widely used bipyridinium herbicides, paraquat (1,1'dimethyl-4,4'-bipyridilium dichloride) and diquat (1, 1'-diethylene-2,2'-bipyridilium dibromide), microorganisms were isolated that would degrade the monohydroxylated pyridines. 2-Hydroxypyridine and 3-hydroxypyridine were hydroxylated by Achromobacter strains (Houghton & Cain, 1972) to pyridine-2,5-diol which was then degraded by the maleamate pathway (Cain et al, 1974), a route also used by Pseudomonas putida when grown on nicotinic acid (Behrman & Stanier, 1957) and by a pseudomonad growing at the expense of picolinamide (Orpin et al, 1972). 4-Hydroxypyridine, however, was degraded by an Agrobacterium sp.…”

“…An alternative mechanism of hydroxylation is involved in the hydroxylation of many heterocyclic compounds, such as uracil (Hayaishi & Komberg, 1952), nicotinic acid (Hughes, 1955;Holcenberg & Stadtman, 1969;Hirschberg & Ensign, 1971a,b), nicotine (Hochstein & Dalton, 1967) or N-methylisonicotinic acid (Orpin et al, 1972). Studies with H21180 have shown that the 02 incorporated into these hydroxylated products is derived from water with NADP+, an artificial dye such as Methylene Blue, or a particulate electron-transport system linked to 02 being required as electron acceptor:…”