Methanogenic degradation of hydroquinone and catechol via reductive dehydroxylation to phenol

Abstract

Fermentative degradation of hydroquinone, catechol, and phenol was demonstrated with nearly‐homogeneous mixed methanogenic cultures obtained from freshwater sediments and sewage sludge by enrichment with the respective phenolic substrates. Gram‐negative short rods predominated in these cultures, together with hydrogen‐ and acetate‐utilizing methanogens. Acetate and methane were the only degradation products. Bacteria enriched with hydroquinone or catechol also degraded phenol and p‐hydroxy‐benzoate, but not resorcinol or resorcylic acids. Phenol was formed as an intermediate during catechol and hydroquinone degradation, indicating that reductive dehydroxylation was the primary event in degradation of these substrates. Inhibition experiments with bromoethanesulfonate and acetylene indicated that catechol, hydroquinone, and phenol degradation depended on a syntrophic co‐operation of fermenting bacteria and hydrogen‐oxidizing methanogens.

Enzymes of anaerobic metabolism of phenolic compounds

“…Examples are the reductive dehydroxylations of 3-hydroxybenzoyl-CoA [38] (and this work) and of 4-hydroxy-3-methylbenzoyl-CoA [39 -411 which play a role in anaerobic 3-hydroxybenzoate, 0-cresol, and 2,4-dimethylphenol degradation. Reductive dehydroxylations play a similar role in anaerobic catechol, hydroquinone, and gentisic acid degradation [17,[42][43][44][45]. It is thought that catechol is carboxylated to protocatechuate which, after activation to protocatechuyl-CoA, is reductively dehydroxylated sequentially ; hydroquinone appears to be carboxylated to gentisate and its conversion to benzoyl-CoA seems to proceed similarly (B. Schink, University of Konstanz, personal communication).…”

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

“…Fermentative degradation of hydroquinone was so far only reported for sludge samples (Young and Rivera 1985) and for enrichment cultures (Szewzyk et al 1985). Strain HQG61 described in this paper is the first anaerobic fermenting bacterium degrading hydroquinone in pure culture.…”

“…The hydroquinone-degrading strain HQG61 was isolated from an anaerobic fixed bed reactor inoculated with a liquid enrichment culture which had been cultivated for more than two years with hydroquinone as sole energy and carbon source (Szewzyk et al 1985). In this highly enriched mixed culture, a stable community had developed which consisted mainly of the hydroquinone-degrading bacteria and two types of methanogenic bacteria, namely, Methanospirillum sp.…”

“…Strain HQG61 was isolated from the enrichment culture HQG6 described in an earlier study (Szewzyk et al 1985), which was originally inoculated with anoxic digestor sludge from the municipal sewage plant in G6ttingen, FRG.…”

“…Two bacteria have been described degrading benzoate in syntrophic coculture with a hydrogen-consuming bacterium (Mountfort et al 1984;Tschech and Schink 1986). No fermenting bacterium degrading phendiols has been isolated in pure culture, but degradability of these compounds under methanogenic conditions has been observed in enrichment cultures and sludge samples (Szewzyk et al 1985;Young and Rivera 1985).…”