Fermentative metabolism of substituted monoaromatic compounds by a bacterial community from anaerobic sediments

Abstract

An anaerobic microbial community containing 4 to 5 different populations capable of degrading syringic acid completely to CH₄ and CO₂ was enriched from freshwater lake sediments. The community can be maintained with syringic acid as sole carbon- and energy source in a defined mineral medium. Syringic acid is converted stoichiometrically according to

$$C_9 H_{10} O_5 + 4H_2 O \to 4{\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 2$}}CH_3 COOH \to 4{\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 2$}}CH_4 + 4{\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 2$}}CO_2$$

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The aromatic ring of several other syringols can be degraded as well. The presence of 3 hydroxy or methoxy substituents seems to be the only condition for successful ring cleavage. Corresponding catechols and guaiacols, however, are converted to 2-hydroxyphenol (catechol); the ring is not cleaved.

Methoxylated syringols are first converted to the corresponding hydroxylated analogs with concomittant formation of CH₄ and CO₂ from the methoxyl carbon. A second population ferments gallic acid and pyrogallol stoichiometrically to 3 mol acetate. Methane formation from acetate is attributed to several methanogens, none of which can be associated with any one of the known acetotrophic ones.