Isolation and characterization of an anaerobic syntrophic benzoate-degrading bacterium from sewage sludge

Abstract

An anaerobic, motile, gram-negative, rod-shaped bacterium is described which degrades benzoate in coculture with an H2-utilizing organism and in the absence of exogenous electron acceptors such as O2, SO 4 = or NO 3 - . The bacterium was isolated from a municipal primary, anaerobic sewage digestor using anaerobic roll-tube medium with benzoate as the main energy source and in syntrophic association with an H2-utilizing sulfate-reducing Desulfovibrio sp. which cannot utilize benzoate or fatty acids apart from formate as energy source. The benzoate utilizer produced acetate (3 mol/mol of substrate degraded) and presumably CO2 and H2, or formate from benzoate. In media without sulfate and with Methanospirillum hungatei (a methanogen that utilizes only H2−CO2 or formate as the energy source) added, 3 mol of acetate and 0.7 mol of methane were produced per mol of benzoate and CO2 was probably formed. Low numbers of Desulfovibrio sp. were present in the methanogenic coculture and a pure coculture of the benzoate utilizer with M. hungatei was not obtained. The generation times for growth of the sulfate-reducing and methanogenic cocultures were 132 and 166h, respectively. The benzoate utilizer did not utilize other common aromatic compounds, C 3 - −C7 monocarboxylic acids, or C4-C6 dicarboxylic acids for growth, nor did it appear to use SO 4 = , NO 3 - or fumarate as alternative electron acceptors. Addition of H2 inhibited growth and benzoate degradation.