Biotransformation of p-toluic acid in anoxic estuarine sediments under a CO 2 or N 2/H 2 atmosphere

Abstract

The composition of the headspace gas affected the growth dynamics of microbial populations and the biotransformation pattern of p-toluic acid in anoxic estuarine sediments. Under CO 2 atmosphere, p-toluic acid was transformed by the sediment microorganisms without a lag period, while under N 2/H 2 atmosphere, p-toluic acid was transformed after a lag period of 55 days. Under the N 2/H 2 atmosphere, the methanogen population, following a rapid increase of almost two orders of magnitude, remained at a high level until just before the onset of biotransformation. We hypothesize that during the lag period, the hydrogenotrophic methanogens were removing the H 2, a step which is essential before the reaction can be exergonic. Acetogenic bacteria did not initiate decarboxylation as the first step of biotransformation under either atmosphere. Neither the methanogens nor the acetogenic bacteria appeared to be directly involved in the biotransformation of p-toluic acid under either atmosphere. Under the CO 2 atmosphere, biotransformation of p-toluic acid involved sulfate-reducing bacteria, while under N 2/H 2, both sulfate-reducing bacteria and other eubacteria were involved.