The measurement of electron transport system activity in river biofilms

The factors affecting the measurement of electron transport system (ETS) activity in river biofilm through the reduction of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT) to iodonitrotetrazolium formazan (INT-formazan) have been studied. Methanol extracts INT-formazan more effectively than either propanol or ethanol. A concentration of 0.02% INT was chosen and samples should be incubated for less than 8 h. ETS activity is optimal at a circumneutral pH. ETS stimulators (NADH, NADPH and succinate) added as a check of the assay produced an increase in INT-formazan indicating that ETS activity was being measured. This assay is quick, easy to use and ideal for field studies.