Dissolved Organic Phosphorus Utilization by Synechococcus

While it is now recognized that dissolved organic phosphorus (DOP) is an important source of phosphorus (P) for phytoplankton growth and productivity in the ocean, the contribution of specific DOP sources to microbial community P demand is not fully understood. We tested the DOP preferences of two strains of marine Synechococcus: the open ocean WH8102 and the coastal WH5701. Preliminary results indicate greater hydrolysis of the P-anhydride compounds 3-polyphosphate (3polyP), followed by adenosine 5’-triphosphate (ATP), than the P-monoester compound adenosine monophosphate (AMP) in culture exudate and in whole cultures. Hydrolysis rates were much greater under phosphate-depleted culture condition, indicating regulation of DOP hydrolysis by ambient phosphate concentration. In addition, we monitored the growth of both strains of Synechococcus in SN media lacking phosphate (-P) or supplemented with either 45 µM phosphate (+P), 3polyP, 45-polyphosphate (45PP), ATP, AMP or glucose-6-phosphate (G6P). We found that both strains could grow similarly on all P sources, except for AMP which sustained virtually no growth for the open ocean strain or very slow growth for the coastal strain. These results confirm the capacity of Synechococcus to utilize different P-anhydride compounds for growth, including longer chains of polyP, while the P-monoester compound AMP appears to be much less bioavailable. Yet, growth on G6P indicates that other P-monoesters may be utilized. We will therefore test a wider range of substrates. Furthermore, targeted proteomics analysis in Synechococcus cultures revealed a number of potential P-hydrolyzing enzymes that could be involved in the transformation of these DOP sources. Overall, these results indicate that inorganic polyphosphates are a key bioavailable source of P for the globally distributed and abundant marine cyanobacteria Synechococcus.