Control analysis of microbial interactions in continuous culture: a simulation study

Abstract

SUMMARY: Metabolic Control Analysis (MCA) has been applied to flux of substrates and products during the growth of a single species and of two interacting species in a chemostat. Single-species growth was described by classical chemostat kinetics and the two-species interaction was commensalism, the first species converting the inflowing limiting substrate to a product which provided the limiting substrate for the second species. For the single species situation, control of flux to product is shared by the dilution rate and bacterial specific growth rate, and control can be quantified in terms of two flux control coefficients CJ D and CJμum1representing the fractional changes in flux resulting from fractional changes in the dilution rate and maximum specific growth rate, respectively. At low dilution rates, dilution rate exerts greater control, whilst CJμm1exceeds CJ D at high dilution rates. In the two-species commensal interaction, additional control on flux to product is exerted by species 2 and may be quantified in a further flux control coefficient CJμm2. Control exerted by a particular species in this interaction increases as factors, e.g. maximum specific growth rate and saturation constant for growth, change to decrease its specific growth rate. Control over flux by a species is also increased by addition of an inhibitor specific to that species and a method is proposed for determining experimentally the flux control coefficient for a species which can be inhibited in this manner.