Species-specific alkaline phosphatase activity in freshwater spring phytoplankton: Application of a novel method

For the first time, in situ alkaline phosphatase activity (APA) was studied at the species level in a natural spring community of freshwater phytoplankton. This was achieved by utilizing a substrate called enzyme labeled fluorescence (ELF), which forms fluorescent precipitates at the site of APA. Samples collected from Lake Erken, Sweden, were assayed with ELF and a number of species belonging to Bacillariophyceae, Chlorophyceae and Dinophyceae were labeled. Within these species we found temporal changes in the percentage of the populations that were ELF labeled. Our results demonstrate that species are not all utilizing AP at the same time, and that within one species, individual cells express different levels of APA. Comparisons between ELF activity and bulk community APA measurements, using standard methods, showed cases both of agreement and disagreement. In this study, we were unable to determine whether some of the fragile flagellates were producing AP. These cells were destroyed in the ELF-labeling process. Overall, we found that the ELF method provided new information on APA in freshwater phytoplankton, and that species-specific measurements are possible, but not for all classes of phytoplankton.