Fermentative degradation of resorcinol and resorcylic acids

Abstract

Anaerobic fermentative degradation of resorcinol and resorcylates was studied in enrichment cultures inoculated with marine or freshwater sediments or digested sludge, e-Resorcylate (3,5-dihydroxybenzoate) was degraded very rapidly to acetate and methane by enrichment cultures inoculated with freshwater sediment or sewage sludge, but degradation was slow in enrichments from marine habitats. The freshwater cultures did not degrade any other related phenolic substrates. Inhibition of methanogenic bacteria by bromoethanesulfonate and acetylene led to enhanced acetate formation indicating homoacetogenic hydrogen oxidation. With resorcinol (1,3-dihydroxybenzene) and/% and 7-resorcylate (2,4- and 2,6-dihydroxybenzoate), two different types of Gram-positive spore-forming strict anaerobes were isolated, which both did not grow with c~-resorcylate. Both were assigned to the genus Clostridium. From freshwater enrichments, six strains were isolated in defined coculture with Campylobacter sp. They fermented resorcinol and /% and 7-resorcylate stoichiometrically to acetate and butyrate. No interspecies hydrogen transfer to methanogenic or other anaerobic bacteria was found. None out of numerous organic nutrients tested substituted for Campylobacter sp. as partner in defined cultures; the nutritive dependence of this bacterium could not be elucidated. Isolates from marine sediments formed acetate and hydrogen from resorcyclic compounds, and depended on syntrophic association with hydrogenscavenging anaerobes such as methanogens.