ALGAE AS COMPETITORS FOR GLUCOSE WITH HETEROTROPHIC BACTERIA(1)

Area of Science:

• Aquatic Ecology
• Microbial Ecology
• Biogeochemistry

Background:

• Dissolved organic carbon (DOC) is a major carbon pool in aquatic systems.
• The role of mixotrophic algae in DOC utilization is less understood compared to heterotrophic bacteria.

Purpose of the Study:

• To test if algae can outcompete bacteria for DOC, reducing concentrations below bacterial needs.
• To investigate the mechanisms of competition for DOC between algae and bacteria.

Main Methods:

• Assessed glucose uptake kinetics in algae and bacteria.
• Conducted competition experiments in chemostats under varying light/dark conditions and glucose supply.
• Determined minimum residual glucose concentrations in cultures.

Main Results:

• Bacteria exhibited higher specific glucose uptake rates than algae.
• Algae outcompeted bacteria in the light but not in the dark.
• Discontinuous glucose supply favored algae.
• Some algae achieved lower residual glucose concentrations than bacteria, especially in the dark.

Conclusions:

• The hypothesis that algae competitively exclude bacteria by lowering DOC was not supported.
• Competition for DOC differs from competition for particulate matter.
• Algal dark uptake of DOC may be significant in aphotic aquatic zones.