APPLICATION OF A DIRECT MICROSCOPIC METHOD OF THE DETERMINATION OF ACTIVE BACTERIA IN LAKES

Electron transport activity was measured in planktonic, freshwater bacteria by determining the number of cells which reduced 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride (INT) to INT-formazan, which was deposited as opague, red, intracellular crystals. Counting was facilitated by application of the malachite green-INT (MINT) method. MINT counts were not significantly different when compared with acridine orange direct counts for determining total bacterial numbers in Florida lakes of varying trophic status. Use of MINT makes it possible to enumerate both active and inactive freshwater bacteria on the same preparation using only bright field microscopy.