SUMMARY: Pool sizes, turnover times and turnover rates of ethanol and acetate in anoxic sediments of Lake Mendota and Knaack Lake and in anoxic sewage digestor sludge were determined by gas chromatography-gas proportional counting techniques. Ethanol accounted for 6, 14 and 2·5% of the total carbon flux to methane in these environments, respectively. The distribution of labelled carbon in the methane and carbon dioxide fractions obtained during incubation of the anoxic materials with C-1 and C-2 labelled acetate and ethanol revealed a significantly higher degree of randomization with ethanol than with acetate tracers. HPLC analysis of sediment pore water preparations revealed that labelled acetate and propionate were formed as intermediates of labelled ethanol degradation, whereas no labelled butyrate was detected. Addition of hydrogen to Knaack Lake sediment samples inhibited ethanol degradation drastically and led to a significant accumulation of labelled butyrate. The above findings together with the results of most probable number enumerations of anaerobic ethanol-degrading bacteria indicate that propionate-forming bacteria contributed significantly to ethanol degradation in Knaack Lake sediment and in sewage sludge.


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