We examined the anaerobic degradation of phenol and the ortho, meta, and para isomers of chlorophenol, methoxyphenol, methylphenol (cresol), and nitrophenol in anaerobic sewage sludge diluted to 10% in a mineral salts medium. Of the 12 monosubstituted phenols studied, only p-chlorophenol and o-cresol were not significantly degraded during an 8-week incubation period. The phenol compounds degraded and the time required for complete substrate disappearance (in weeks) were: phenol (2), o-chlorophenol (3), m-chlorophenol (7), o-methoxyphenol (2), m- and p-methoxyphenol (1), m-cresol (7), p-cresol (3), and o-, m-, and p-nitrophenol (1). Complete mineralization of phenol, o-chlorophenol, m-cresol, p-cresol, o-nitrophenol, p-nitrophenol, and o-, m-, and p-methoxyphenol was observed. In general, the presence of Cl and NO2 groups on phenols inhibited methane production. Elimination or transformation of these substituents was accompanied by increased methane production, o-Chlorophenol was metabolized to phenol, which indicated that dechlorination was the initial degradation step. The methoxyphenols were transformed to the corresponding dihydroxybenzene compounds, which were subsequently mineralized.

Anaerobic biodegradation of phenolic compounds in digested sludge.

Lignin as a Marker in Digestion Studies: a Review

From an anaerobic enrichment culture with vanillate as substrate, a catechol-degrading lemon-shaped nonsporing sulfate-reducing bacterium, strain NZva20, was isolated in pure culture. Growth occurred in defined, bicarbonate-buffered, sulfide-reduced freshwater medium with catechol as sole electron donor and carbon source. Catechol was completely oxidized to CO2 with an average growth yield of 31 g cell dry mass per mol of catechol, corresponding to 9.5 g cell dry mass per mol of sulfate reduced. Further substrates utilized as electron donors and carbon sources were resorcinol, hydroquinone, benzoate and several other aromatic compounds, hydrogen plus carbon dioxide, formate, lactate, pyruvate, alcohols including methanol, dicarboxylic acids, acetate, propionate and higher fatty acids up to 18 carbon atoms. Instead of sulfate, sulfite, thiosulfate, dithionite or nitrate served as electron acceptors. Nitrate was reduced to ammonium. Strain NZva20 is the first bacterium in which the complete oxidation of organic substrates is linked to the ammonification of nitrate. Elemental sulfur was not utilized as electron acceptor. In the absence of an electron acceptor slow growth occurred on pyruvate or fumarate. The G+C content of the DNA of strain NZva20 was 52.4 mol%. Cytochromes were present. Desulfoviridin could not be detected. Strain NZva20 is described as type strain of a new species, Desulfobacterium catecholicum sp. nov.

Complete oxidation of catechol by the strictly anaerobic sulfate-reducing Desulfobacterium catecholicum sp. nov.

Aromatic compounds comprise the second largest group of natural products (Fig. 1); in addition a variety of xenobiotics are man-made aromatic pollutants. They are metabolized by microorganisms following two fundamentally different strategies: Under aerobic conditions, aromatic compounds are transformed by monooxygenases and dioxygenases into a few central intermediates such as catechol, protocatechuate and gentisate. These dihydroxylated compounds are suitable for an oxidative cleavage of the aromatic ring (the pertinent aerobic literature will not be covered here but see Chapter 11 by Smith). Under anoxic conditions, aromatic compounds have to be transformed by other means than by oxygenases. It is now proven that numerous low molecular weight aromatic compounds are degraded by different groups of anaerobic bacteria (early reports by Tarvin and Buswell 1934; Dutton and Evans 1967) and that the aromatic ring structures are reductively attacked, as proposed by the late W.C. Evans (Dutton and Evans 1969; Balba and Evans 1977; Evans 1977; Williams and Evans 1975; Evans and Fuchs 1988). It has to be pointed out, however, that there is no evidence for a significant anaerobic degradation of polymeric high molecular weight aromatics such as lignins, which represent probably more than half of the aromatic compounds (Hackett et al. 1977; Zeikus 1980; Young and Frazer 1987).

Biochemistry of anaerobic biodegradation of aromatic compounds

Revue. Biochemical mechanisms of anaerobic metabolism. Photometabolism. Nitrate-dependent aromatic metabolism. Sulphate-dependent aromatic metabolism. Methanogenic fermentation of aromatic compounds. Anaerobic lignin degradation

https://sfamjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2672.1984.tb01404.x

Evans Wc

Papers

The methanogenic fermentation of plant phenolics [proceedings].