Can bacteria outcompete phytoplankton for phosphorus? a chemostat test

Area of Science:

• Aquatic microbiology
• Limnology
• Nutrient cycling

Background:

• Bacterioplankton are traditionally studied for mineralization processes in lakes.
• Emerging research indicates bacterioplankton may significantly compete with phytoplankton for phosphorus.
• Understanding this competition is crucial for aquatic ecosystem dynamics and nutrient availability.

Purpose of the Study:

• To investigate the competitive interactions for phosphorus between a freshwater bacterium (Pseudomonas paucimobilis) and a phosphorus-limited alga (Synedra ulna var. danica).
• To determine the influence of exogenously supplied organic carbon on bacterial and algal biomass.
• To assess the predictive accuracy of short-term phosphorus uptake ratios for long-term growth.

Main Methods:

• Chemostat cultures were utilized to simulate lake conditions and control nutrient supply rates.
• Experiments involved co-culturing Pseudomonas paucimobilis with Synedra ulna var. danica.
• Short-term (32)P orthophosphate uptake experiments were conducted to measure phosphorus assimilation rates.

Main Results:

• Pseudomonas paucimobilis successfully outcompeted Synedra ulna var. danica for phosphorus across a range of supply rates.
• Increased exogenous organic carbon availability led to enhanced bacterial biomass and reduced algal biomass.
• Bacterial to algal phosphorus uptake ratios in short-term experiments accurately predicted their relative long-term growth.

Conclusions:

• Freshwater bacteria can be significant competitors for phosphorus against phytoplankton, influencing algal populations.
• Organic carbon availability plays a key role in modulating the outcome of bacterial-algal competition for phosphorus.
• Short-term phosphorus uptake measurements provide a reliable method for forecasting long-term competitive dynamics in aquatic microbial communities.