ENUMERATION OF ACETOGENS BY A COLORIMETRIC MOST-PROBABLE-NUMBER ASSAY

Anaerobic O demethylation by acetogenic bacteria often is the first st ep in the mineralization of methoxylated aromatic compounds in anoxic environments, In this reaction, an ether bond is cleaved and the resul ting methyl group is metabolized via the acetyl coenzyme A pathway (ac etogenesis). Anaerobic O demethylation was used to assess acetogen pop ulations, Environmental samples were diluted in anaerobic medium conta ining 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 d evelopment of a yellow color in the medium, which can be detected by e ye and monitored spectrophotometrically. High-performance liquid chrom atography 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 populatio ns in environmental samples.