The Measurement of Electron Transport System Activity in Freshwater Benthic and Planktonic Samples

The measurement of electron transport system (ETS) activity in freshwater benthic and planktonic samples was examined. Significant improvements in sensitivity were obtained by increasing the concentration of substrates and of Triton X-100 in the extraction buffer and by changing the buffer system. The mechanical homogenization procedures which have been used previously to extract the enzymes were shown to be inadequate yielding, at best, 25% of the activity obtained by ultrasonication. The yield of enzymes from sediments was greatly affected by the degree of dilution used and previously published methods would appear to be inadequate. ETS activity correlated well with biological oxygen uptake and, in individual water and sediment profiles, with microbial numbers and biomass. At a more general level, however, the ETS: biomass ratio showed considerable variation.