CO 2 -dependent fermentation of phenol to acetate, butyrate and benzoate by an anaerobic, pasteurised culture
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O R I G I N A L PA P E R
Anna Karlsson · Jörgen Ejlertsson · Bo H. Svensson
CO2-dependent fermentation of phenol to acetate, butyrate and benzoate by an anaerobic, pasteurised culture
Received: 27 August 1999 / Revised: 28 February 2000 / Accepted: 16 March 2000 / Published online: 14 April 2000 © Springer-Verlag 2000
Abstract Fermentative degradation of phenol was studied using a non-methanogenic, pasteurised enrichment culture containing two morphologically different bacteria. Phenol was fermented to benzoate, acetate and butyrate and their relative occurrence depended on the concentration of hydrogen. Proportionately more benzoate was formed with high initial levels of H2. The influence of PH2 on the fermentation pattern was studied both in dense cell suspensions and in growing cultures by addition of hydrogen. An increase in growth yield (OD578) was observed, compared to controls, as a consequence of phenol degradation; however, the increase was less in H2-amended treatments, in which most of the phenol ended up as benzoate. The degradation of phenol in the dense cell suspension experiments was dependent on CO2. Benzoate was not degraded when added as a substrate to the growing culture. This is, to our knowledge, the first report concerning the fermentative degradation of phenol to nonaromatic products. Key words Phenol fermentation · Reductive dehydroxylation · Hydrogen partial pressure · Ring cleavage
Introduction Many micro-organisms can degrade phenol aerobically or anaerobically. Pure cultures of anaerobic bacteria can completely oxidise phenol to carbon dioxide using nitrate, ferric iron or sulfate as the terminal electron acceptor (Tschech and Fuchs 1987; Kuever et al. 1993; Lovley et al. 1993; and reviewed in Heider and Fuchs 1997b). Under conditions in which CO2 is the only external electron acceptor available, the complete degradation of phenol to
A. Karlsson (✉) · J. Ejlertsson · B.H. Svensson Department of Water and Environmental Studies, University of Linköping, 58183 Linköping, Sweden e-mail: [email protected], Tel.: +46-13-282955, Fax: +46-13-133630
acetate is only possible in bacterial consortia in which hydrogen-consuming bacteria, i.e. methanogens or homoacetogens, keep the hydrogen and acetate levels low enough to allow the otherwise endergonic reaction (Eq. 1) to proceed. C6H5OH+5H2O→3CH3COO-+2H2+3H+ ∆G°′ =5.65 kJ mol-1 phenol
(1)
At least two different phenol degradation pathways have been suggested to occur under methanogenic conditions. Since Knoll and Winter (1987) first reported on benzoate formation from phenol, a degradation route via benzoylCoA/benzoate has received the most attention (Knoll and Winter 1989; Kobayashi et al. 1989; Béchard et al. 1990; Zhang and Wiegel 1990). Gallert and Winter (1994) proposed a degradation pathway in which phenol is transformed via carboxylation, thioester formation and dehydroxylation to benzoyl-CoA, which is thereafter converted to benzoate. The benzoate (or benzoyl-CoA) formed is then degraded through ring reduction and β-oxidation to aceta
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