Electrode system for determination of microbial cell populations in polluted water

Microbial cell populations in polluted water were determined by using a fuel cell-type electrode. The electrode was composed of a Pt anode, a Pt-K3Fe(CN)6-K4Fe(CN)6 cathode, and a cation-exchange membrane for separating two electrode compartments. The principle of microbial cell number determination is based on sensing a redox dye reduced by microorganisms with the electrode. Sample solutions containing microorganisms, a redox dye (thionine), and peptone were purged with oxygen-free nitrogen during the determination. A linear relationship was obtained between the increasing rate of current and the number of microbial cells measured by the colony count method above 10(4) cells per ml. The determination time varied with the number of microbial cells determined from 20 to 60 min for 3.6 x 10(6) and 3.6 x 10(4) cells per ml, respectively.