ABSTRACT: Competitive ability for phosphorus of 2 heterotrophic bacteria, isolated from the photic zone of a lake, was investigated by a growth kinetic characterization in batch cultures using a radioactive tracer. Key characteristics chosen were based on a competition model verified under both steady state and non steady state conditions in previous studies. The characterization included determination of P requirement, uptake kinetic parameters and release rates of dissolved inorganic phosphate (P_i). The 2 bacteria exhibited different kinetic properties that may reflect differences in competitive strategies. Strain 3h seemed to be adapted to competition at more transient or pulsed supply modes of P_i, as reflected by its P-specific maximum uptake rate, which was 4 times higher than that of strain 2g. Strain 2g, on the other hand, seemed to be a better competitor at uniform or moderately pulsed P_i supply modes. This is due to a better ability to maintain positive net P_i uptake at low concentrations, with the critical concentration for positive net uptake being a factor of 2 lower for strain 2g than for strain 3h. A comparison with typical values of kinetic parameters published for cyanobacteria and green algae suggest that cyanobacteria may be better competitors than the heterotrophic bacteria at transient supply modes of P_i, whereas green algae have a comparable or better ability than the heterotrophic bacteria to compete for P at uniform supply modes of P_i. These conclusions are based on relatively few data, with considerable within-group variation, and should therefore be considered with caution.

KEY WORDS: Bacteria · Phosphorus · Nutrients · Uptake · Competition · Elemental ratios

Published in AME Vol. 14, No. 2 (1998) on February 13
Print ISSN: 0948-3055; Online ISSN: 1616-1564. Copyright © Inter-Research, Oldendorf/Luhe, 1998