Comparative phosphorus nutrition of the marine cyanobacterium Synechococcus WH7803 and the marine diatom Thalassiosira weissflogii

Phosphate uptake kinetics of Synechococcus sp. WH7803 and Thalassiosira weissflogii were studied in axenic batch culture. Phosphate-replete Synechococcus sp. WH7803 cells have a lower affinity for inorganic phosphate (Pi) (K-s = 67 mu mol l(-1)) than Pi-starved cells (K-s = 3.1 mu mol l(-1)). The K, of Pi-starved cells increased similar to 5-fold (K-s = 14-20 mu mol l(-1)) following incubation in the dark or upon addition of the uncoupler carbonyl cyanide p-trifluoromethoxy phenylhydrazone (FCCP). Pi-replete and Pi-starved T. weissflogii exhibit similar affinities for phosphate (K-s of 6.6 and 8.9 mu mol l(-1), respectively). In both cases, K, values are increased by incubation in the dark. The rate of Pi uptake, when the organisms were cultured in competition with each other, was dependent on the Pi state of the cells: Pi-replete T.weissflogii displayed faster Pi uptake than Pi-replete Synechococcus sp. WH7803, whereas Pi-starved T.weissflogii displayed a slower rate of uptake than Synechococcus sp. WH7803. Both T.weissflogii and Synechococcus sp. WH7803 could take up phosphorus (P) when it was supplied as a range of organic phosphate compounds, the phosphate groups being cleaved from the organic phosphate molecule and incorporated. Both organisms could cleave and incorporate phosphorus from dCTP, p-nitrophenyl phosphate, glucose-6-phosphate and glycerol phosphate; however, only T. weissflogii grew with cyclic AMP as the sole P source. Uptake kinetics of P from the nucleotide dCTP were determined; phosphate-replete Synechococcus sp. WH7803 cells have a lower affinity for P from dCTP (K-s = 60 mu mol l(-1)) than Pi-starved cells (K-s = 8 mu mol l(-1)). Pi-replete and Pi-starved T. weissflogii exhibit similar affinities for P from dCTP (K-s values are 43 and 48 mu mol l(-1), respectively).