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Aquatic Microbial Ecology

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AME 14:119-127 (1998)  -  doi:10.3354/ame014119

Evaluation of competitive ability of two heterotrophic planktonic bacteria under phosphorus limitation

Olav Vadstein*

Trondhjem Biological Station, Norwegian University of Science and Technology, N-7034 Trondheim, Norway

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 (Pi). 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 Pi, 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 Pi supply modes. This is due to a better ability to maintain positive net Pi 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 Pi, whereas green algae have a comparable or better ability than the heterotrophic bacteria to compete for P at uniform supply modes of Pi. These conclusions are based on relatively few data, with considerable within-group variation, and should therefore be considered with caution.

Bacteria · Phosphorus · Nutrients · Uptake · Competition · Elemental ratios

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