A COMPARISON OF VIABILITY AND VITALITY TESTING METHODS AFTER BENCH SCALE UV- AND HEAT-TREATMENT OF THE DIATOM THALASSIOSIRA WEISSFLOGII

Abstract

Thalassiosira weissflogii, a marine diatom, was inactivated using two bench-scale treatment methods: ultraviolet radiation (UV-C) and a water bath (50°C). After treatment with either UV-C or heat, and a 24-hour dark incubation, cultures were analyzed using a range of monitoring methods to assess viability and vitality: serial dilution culture most probable number (SDC-MPN), cellular ATP concentration, vital stains, and chlorophyll fluorescence. T. weissflogii viable cell concentration was reduced by 3-log after 6 minutes of heat exposure or 148 mJ/cm2 of UV-C radiation. UV-C treatment is far more energy efficient, using less than 1% of the equivalent input energy required for heat treatment. Viability, as determined through a growth assay, is compared against the other monitoring methods. Vitality testing was demonstrated to produce false positive results, especially for the UV-C treated cells.