Degradation of phenol via carboxylation to benzoate by a defined,obligate syntrophic consortium of anaerobic bacteria

Summary An obligate syntrophic culture was selected in mineral medium with phenol as the only carbon and energy source. The consortium consisted of a short and a long rod-shaped bacterium and of low numbers of Desulfovibrio cells, and grew only in syntrophy with methanogens, e. g. Methanospirillum hungatei. Under N₂/CO₂, phenol was degraded via benzoate to acetate, CH₄ and CO₂, while in the presence of H₂/CO₂ benzoate was formed, but not further degraded. When 4-hydroxybenzoate was fed to the mixed culture, it was decarboxylated to phenol prior to benzoate formation and subsequent ring cleavage. Isolation of pure cultures of the two rod-shaped bacteria failed. Microscopic observations during feeding of either 4-hydroxybenzoate, phenol or benzoate implied an obligate syntrophic interdependence of the two different rod-shaped bacteria and of the methanogen. The non-motile rods formed phenol from 4-hydroxybenzoate and benzoate from phenol, requiring an as yet unknown co-substrate or co-factor, probably cross-fed by the short, motile rod. The short, motile rodshaped bacterium grew only in syntrophy with methanogens and degraded benzoate to acetate, CO₂ and methane. Desulfovibrio sp., present in low numbers, apparently could not contribute to the degradation of phenol or 4-hydroxybenzoate.