Enumeration of acetogens by a colorimetric most-probable-number assay.

Anaerobic O demethylation by acetogenic bacteria often is the first step in the mineralization of methoxylated aromatic compounds in anoxic environments. In this reaction, an ether bond is cleaved and the resulting methyl group is metabolized via the acetyl coenzyme A pathway (acetogenesis). Anaerobic O demethylation was used to assess acetogen populations. Environmental samples were diluted in anaerobic medium containing a methoxylated aromatic substrate (vanillate) and titanium(III), and acetogen titers were estimated by the most-probable-number (MPN) method. Complex formation between Ti(III) and vicinal hydroxyl groups of the aromatic products of anaerobic O demethylation results in the development of a yellow color in the medium, which can be detected by eye and monitored spectrophotometrically. High-performance liquid chromatography analysis of the yellow MPN tubes showed that they contained the product of anaerobic O demethylation of vanillate (protocatechuate). This assay was used to enumerate O-demethylating acetogen populations in environmental samples.