ANAEROBIC DEGRADATION OF ALPHA-RESORCYLATE BY THAUERA-AROMATICA STRAIN AR-1 PROCEEDS VIA OXIDATION AND DECARBOXYLATION TO HYDROXYHYDROQUINONE

Anaerobic degradation of alpha-resorcylate (3,5-dihydroxybenzoate) was studied with the denitrifying strain AR-1, which was assigned to the described species Thauera aromatica. alpha-Resorcylate degradation doe s not proceed via the benzoyl-CoA, the resorcinol, or the phloroglucin ol pathway. Instead, alpha-resorcylate is converted to hydroxyhydroqui none (1,2,4-trihydroxybenzene) by dehydrogenative oxidation and decarb oxylation. Nitrate, K-3[Fe(CN)(6)], dichlorophenol indophenol, and the NAD(+) analogue 3-acetylpyridine adeninedinucleotide were suitable el ectron accepters for the oxidation reaction; NAD(+) did not function a s an electron acceptor. The oxidation reaction was strongly accelerate d by the additional presence of the redox carrier phenazine methosulfa te, which could also be used as sole electron acceptor. Oxidation of a lpha-resorcylate with molecular oxygen in cell suspensions or in cell- free extracts of a-resorcylate- and nitrate-grown cells was also detec ted although this bacterium did not grow with alpha-resorcylate under an air atmosphere. alpha-Resorcylate degradation to hydroxyhydroquinon e proceeded in two steps. The alpha-resorcylate-oxidizing enzyme activ ity was membrane-associated and exhibited maximal activity at pH 8.0. The primary oxidation product was not hydroxyhydroquinone. Rather, for mation of hydroxyhydroquinone by decarboxylation of the unknown interm ediate in addition required the cytoplasmic fraction and needed lower pH values since hydroxyhydroquinone was not stable at alkaline pH.