Similarity between biotransformation rates and turnover rates of organic matter biodegradation in anaerobic environments

Abstract

Methods have been developed to assess the rate of substrate transformation in anoxic environments based upon the rate of product formation. Transformation rate constants based on the production of gases, 14CH 4 and 14CO 2, ( k g) averaged 96.7% (SD = 14%) of the turnover rate constant ( k) based upon loss of [U- 14C]glucose, [I- 14C]lactate, [I- 14C]-or [2- 14C]acetate when examined in sewage sludge or lake sediments. Lower k g values, ≈ 1 2 of k , were obtained from [3- 14C]lactate in all habitats because [3-C]lactate produced [2-C]acetate which was later consumed by methanogens. Inclusion of volatile organic acid production in the transformation rate constant determinations ( k gv = 14 CH 4 , [ 14C]volatile organic acids) resulted in a k gv = 0.89 of the value for k for [3-C]lactate as expected, transformation rate constants decreased as the food chain was ascended with acetate > lactate > glucose. Cellulose, a polymer whose turnover rate constant could not be determined, was transformed considerably slower than glucose and k g = k gv. Transformation rate constants are a rapid and accurate technique for assessing turnover of specific metabolites in anoxic habitats and may be suited for examining the decomposition of polymers and compounds whose loss from ecosystems are difficult to quantify.