Selection and Coexistence in a Bioreactor

The bioreactor (continuous flow stirred tank reactor) has become an ubiquitous experimental device that also allows the study of selection, bistability or coexistence of competing species in the laboratory. The steady state solutions (and relaxation times of two mechanisms) of a number of simple mechanisms are calculated that contain two competing autocatalytic steps followed by a third step. For simplicity the third step is chosen to be either a first order conversion between the rival species (mechanism II), an additional autocatalytic conversion (mechanism III), or an annihilation step between the two species (mechanism IV). Selection may be displayed by all mechanisms studied, coexistence only by mechanisms II and III, whereas IV shows bistability where either one of two steady states are reached depending upon initial concentrations. A number of relevant biological systems are described and qualitatively compared with theory.