THE ROLE OF EXTRACELLULAR PHOSPHATASES IN AQUATIC ENVIRONMENTS
Keywords:extracellular phosphatases, phosphorus, plankton, epiphyton, aquatic ecosystem.
Enzymatic hydrolysis of organic matter is a major process in nutrient cycling in aquatic environments, allowing nutrients retained in the particulate and dissolved organic fractions to become available to aquatic microorganisms, in this paper, a literature review about the role of extracellular phosphatases in aquatic environments is presented. Special emphasis will be given to the dynamics of extracel1ular phosphatase activity in Brazilian ecosystems. Extracelular phosphatases catalyze the hydrolysis of organic phosphorus compounds to inorganic phosphate. These enzymes are produced mainly by algae, bacteria and zooplankton, and may play an important role in structuring plankton communities in aquatic ecosystems. However, it is not well known to which extent phosphatase activity is important to provide inorganic phosphate to plankton. The quantity and quality of dissolved organic compounds are key factors that control phosphatase activity in natural waters. Moreover, phosphatase synthesis is repressed by high concentrations of inorganic phosphate and it is depressed when phosphate reaches low concentrations in the medium. These characteristics constitute the theoretical basis for the use of extracellular phosphatase activity as a measure of phosphorus deficiency of algae in culture and in the natural phytoplankton community, although some restrictions to this approach have been suggested. In this paper, methods available to measure the activity of phosphatases, and their activity in sediments and in epiphytic communities are briefly discussed.