A COMPARISON OF TETRAZOLIUM REDUCTION AND FDA HYDROLYSIS WITH OTHER MEASURES OF MICROBIAL ACTIVITY

Two simple enzyme assays are described as surrogates for microbial activity in a range of environmental materials. The two assays rely on different enzyme systems, one (the fluorescein diacetate method) is sensitive to both free and membrane-bound enzymes, while the other (the INT assay) measures the activity of the succinate dehydrogenase complex bound to intracellular membranes. Both methods are shown to correlate closely with both the ATP content and cell density of pure and mixed microbial cultures, while the FDA activity of leaf litter was also shown to correlate closely with maximum glucose-stimulated respiration rate. It is concluded that the assays are good alternatives to more conventional and labour-intensive methods of measuring total microbial activity, and that the INT assay is best-suited for measuring cell density whereas the FDA assay is better for estimates of decomposer activity.