Degradation of hydroquinone, gentisate, and benzoate by a fermenting bacterium in pure or defined mixed culture

Abstract

Abstract. From a methanogenic fixed-bed reactor fed with hydroquinone as sole energy and carbon source, a rodshaped bacterium was isolated in pure culture which could degrade hydroquinone and gentisate (2,5-dihydroxybenzoate). In syntrophic coculture with either Desulfovibrio vulgaris or Methanospirillum hungatei, also benzoate could be degraded. Other substrates such as sugars, fatty acids, alcohols, and cyclohexane derivatives were not degraded. Sulfate, sulfite, or nitrate were not used as external electron acceptor. The isolate was a Gram-negative, non-motile, nonsporeforming strict anaerobe; the guanine-plus-cytosine content of the DNA was 53.2_+ 1.0 mol%. In pure culture, hydroquinone was degraded to acetate and benzoate, probably via an intermediate carboxylation. In syntrophic mixed cultures, all three substrates were converted completely to acetate. Phenol was never detected as a fermentation product.

Soils contaminated with explosives: Environmental fate and evaluation of state-of-the-art remediation processes (IUPAC Technical Report)

“…Reductive deamination reactions were postulated first for 2-aminobenzoate degradation by methanogenic enrichment cultures [285]. Reductive dehydroxylation of gentizate to benzoate and acetate was demonstrated in the fermenting bacterium HQGO1 [286].…”

Evidence of reversed electron transport in syntrophic butyrate or benzoate oxidation by Syntrophomonas wolfei and Syntrophus buswellii

“…It seems probable that benzoate-grown cells of S. busweIlii have the ability to activate crotonate; however, this must be confirmed by enzyme measurements in cell-free extracts of the syntrophically grown culture. A recently isolated syntrophically benz0ate-oxidizing bacterium can grow in pure culture with gentisate or hydroquinone as substrate (Szewzyk and Schink 1989;Gomy and Schink 1994).…”

Hydroquinone degradation via reductive dehydroxylation of gentisyl-CoA by a strictly anaerobic fermenting bacterium

“…Also reductive elimination of one of the hydroxyl groups to form phenol as an intermediate is improbable since dehydroxylation has been demonstrated so far only for coenzyme A-linked aromatic compounds. Carboxylation of hydroquinone to gentisate as the first reaction in anaerobic degradation has been proposed earlier for the fermenting bacterium strain HQG61 (Szewzyk and Schink 1989). This bacterium degrades hydroquinone to benzoate and acetate in pure culture, and oxidizes hydroquinone, gentisate, and benzoate to acetate and CO2 in the presence of a methanogenic partner bacterium.…”

“…Since the carboxylation of hydroquinone is an endergonic process (Table 4, (3)) it was not surprising that the cell yield Ys [g tool-l] of strain HQG61 was 3.6 g tool -1 higher with gentisate than with hydroquinone (Szewzyk and Schink 1989). If YATP [g X mol ATP-1] is assumed to be 10 g x tool A T P -1 (Stouthamer 1979) and the free energy for irreversible ATP synthesis to be 70 kJ x mol A T P -~ (Thauer et al 1977), strain HQG61 would gain 25 kJ per mol more from gentisate than from hydroquinone.…”