Chemical composition and phosphate uptake kinetics of limnetic bacterial communities cultured in chemostats under phosphorus limitation

Natural bacterial communities were grown in chemostats diluted with filtered lake water manipulated to yield phosphorus limitation. The results suggested P limitation of the bacteria when the P : C and the surplus : C ratios were between 17–120 and 2.7–100 µg P(mg C)−1, respectively. These high values indicate that heterotrophic bacteria are net consumers of phosphate and that they sequester a considerably higher fraction of the particulate P in lakes than expected from their biomass in terms of carbon. Estimates of maximal uptake velocity and affinity for phosphate at low concentrations for the mixed bacterial communities were influenced by the degree of P limitation. A review of published data indicates that under P limitation bacteria are superior to phytoplankton in taking up phosphate at low concentrations, whereas their abilities are comparable at saturation.