Competition between phytoplankton and bacteria: exclusion and coexistence

Area of Science:

• Microbial Ecology
• Theoretical Ecology
• Mathematical Biology

Background:

• Resource-based competition in continuous culture is well-studied for bacteria (Monod, Contois models) and phytoplankton (Droop models).
• Theoretical models for homogeneous populations predict competitive exclusion, where only one species survives.
• Previous studies validated competitive exclusion experimentally and in natural environments.

Purpose of the Study:

• To generalize existing models by studying competition among three distinct microorganism types.
• To investigate the competitive dynamics between planktonic bacteria, aggregating bacteria, and free phytoplankton.
• To determine the conditions under which coexistence or competitive exclusion occurs.

Main Methods:

• Utilized a generalized Monod model for planktonic bacteria.
• Employed a Contois model for aggregating bacteria.
• Applied a Droop model for free phytoplankton.
• Analyzed substrate concentration evolution under competitive pressure in a chemostat.

Main Results:

• Demonstrated that competition leads to coexistence between several aggregating bacterial species and one free species (bacterial or phytoplankton).
• Observed that all other free species are washed out.
• Identified three distinct competition outcomes based on substrate subsistence concentration and species type.

Conclusions:

• The study generalizes microbial competition theory by incorporating different microbial strategies (planktonic, aggregating, phytoplankton).
• Coexistence of aggregating bacteria with a single superior free competitor is a key outcome.
• Theoretical predictions are extended to more complex microbial community structures.