Dissolved organic phosphorus regeneration by bacterioplankton: 5'-nucleotid-ase activity and subsequent phosphate uptake in a mesocosm enrichment experiment

Bacterial 5'-nucleotidase activity was studied during a mesocosm enrichment experiment on the SW coast of Finland, Baltlc Sea. 5'-nucleotidase activlty and uptake of 3 2 ~0 4 hydrolyzed from 5'nucleotide was compared to direct 3 2 ~0 4 uptake measurements and other nutrient data. The enzyme was not repressed by elevated PO, concentrations, and it hydrolyzed orthophosphate from dissolved organic phosphorus in amounts which were quantitatively significant in the phosphorus dynamics of the community. Bacteria partly assimilated the hydrolyzed PO,, but depending on nutritional conditions, 0 to 80 YO of the hydrolyzed PO4 was released to the environment. Temporal uncoupling between nutrient assimilation and growth was evident for both bacteria and algae. 5'-nucleotidase represented a mechanism of phosphorus regeneration which supports the concept of closely integrated microaggregates having an important role in nutrient cycles of nutrient-depleted surface waters O Inter-Research/Printed in F. R. Germany