Initial steps of catabolism of trihydroxybenzenes in Pelobacter acidigallici

The initial steps of the anaerobic degradation of trihydroxylated aromatic monomers were investigated in a strain (AG2) isolated on gallic acid and identified as Pelobacter acidigallici. Kinetic studies showed that strain AG2 fermented gallic acid into acetate with a transient accumulation of pyrogallol and phloroglucinol in the medium. In addition phloroglucinol was produced from all other trihydroxylated aromatic monomers and pyrogallol from 2,3,4-trihydroxybenzoate. Although protocatechuate did not support growth of the organism, it was partially decarboxylated by resting cells of strain AG2. Cell free extract of strain AG2 catalysed the oxidation of NADPH in presence of resorcinol, 2,4,6-trihydroxybenzoate and phloroglucinol. However, comparison of activities indicated that the latter was the true physiological electron acceptor. Phloroglucinol and its reduction product dihydrophloroglucinol appeared thus to play a key role in metabolism of trihydroxybenzenes and a unified pathway, involving a decarboxylation of trihydroxybenzoates, a para transhydroxylation of pyrogallol into phloroglucinol and the formation of dihydrophloroglucinol, was proposed.