A COMPARISON OF INT-FORMAZAN METHODS FOR DETERMINING BACTERIAL-ACTIVITY IN STREAM ECOSYSTEMS

We investigated different procedures for using a fluorescent stain and dehydrogenase indicator technique for detection of respiring bacteria in two stream ecosystems in the southeastern United States. A modifie d filter-transfer-freeze (FTF) procedure was useful in detecting iodon itrotetrazolium formazan (INT) crystals in unattached bacteria. This t echnique did not enhance detection of INT crystals in particle-bound e pilithic and epipelic bacteria. No significant differences were found between pre-stained polycarbonate filters mounted with immersion oil a nd those mounted with glycerol, although we preferred glycerol because of its optical clarity. In contrast to previous studies, we did not f ind that immersion oil dissolved INT crystals within bacterial cells e ven after a period of 24 h. Percentages of active bacteria in comparab le habitats were not significantly different between a sandstone and a carbonate stream. However, benthic habitats (epilithon and epipelon) had significantly higher percentages of active bacteria (approximately 15-26%) than overlying stream water (approximately 2-7%) at all sites on all sampling dates.