Phytoplankton extracellular phosphatases: Investigation using the ELF (enzyme labelled fluorescence) technique

Phosphorus deficiency is frequently the limiting factor in phytoplankton growth and the major source of selective pressure on single populations in a variety of aquatic environments. Phytoplankton species have several mechanisms that allow them to overcome phosphorus starvation, such as high-affinity uptake of orthophosphate (Pi), stand-by energy metabolism or utilization of phosphorus from stored polyphosphates. This short review is focused on the production of extracellular phosphatases that is usually accompanied by high-affinity uptake of Pi. Extracellular phosphatases are localized on thecell membrane, where they catalyze the liberation of Pi from various organic compounds that are too large to be directly transported into the cell. The production of extracellular phosphatases is not a general response to starvation in phytoplankton; it is a species-specific or cell-specific feature. The ELF (Enzyme Labelled Fluorescence) technique enables direct visualization of the sites of enzymatic activity and therefore gives detailed information about the physiological status of natural phytoplankton.