Microbial Activity in Lake Sediments with Particular Reference to Electrode Potential Gradients

Abstract

Microbial activity was determined along electrode potential gradients within sediments, and along sediment surfaces in a stratified eutrophic lake. There was evidence of a change from a tricarboxylic acid cycle-based metabolism to a fermentative 1 with decreasing electrode potential. A more detailed examination of the stratification of the microbial community showed that the activities of enzymes associated with energy metabolism (in this case electron transport) were highest on electrode potential gradients. This was observed within a sediment core on a millimeter-depth scale, and over several meters at the surface of sediments, on a transect which ran from oxic littoral muds to the anoxic profundal zone. Microbial hydrolytic enzymes, such as protease and amylase, were most active at the sediment surface, where the highest concentrations of substrates might be expected.