Simulation Study of Competition between Two Types of Microorganisms with Antagonistic Relationships in a Completely Mixed Reactor

Abstract

A simple dynamic model of competition between two types of microorganisms, one of which produces an inhibitory substance in an ideal chemostat, was developed to study the survival mechanism of an exogenous microbial strain introduced into an ecosystem possessing antagonistic activity against it. Numerical simulations of the model were carried out in 12 cases depending on the disposition of the growth rate curves of the two types of microorganisms and on the sensitivity of the microorganisms against the inhibitory substance. From the results, it was demonstrated that production of an inhibitory substance gives its producer a chance to exclude the competitor under conditions in which the producer would be otherwise excluded by the competitor. It was also found that production of a substance which is inhibitory not only against the competitor but also against the producer itself (autoinhibitory) allows the two microbial strains to coexist under conditions in which the competitor would otherwise be excluded. It was suggested that production of some inhibitory substances and tolerance to such substances are desirable characteristics for exogenous microorganisms to survive in microbial ecosystems, and a large inoculum density of exogenous microorganisms has a positive effect on their survival rate in some cases.