Ecological dynamics of an acetate producer <i>E</i>. <i>coli</i> strain P and an acetate consumer strain C in a chemostat.

<p>(A) Interactions between the strains. Producer strain P (blue) produces acetate (black) at a rate <i>p</i>_{<i>ac</i>,<i>P</i>} and consumes glucose (grey) as its sole carbon source. Consumer strain C consumes mainly acetate but can also consume glucose at some rate <i>c</i>_{<i>glc</i>,<i>C</i>}. Both strains may also consume other nutrients or produce other metabolic by-products, which are not shown. (B) Dynamics in a chemostat for an acetate production flux by P of 2.6 (<i>p</i>_{<i>ac</i>,<i>P</i>} = 2.6 mmol∙gDW^-1h^-1). The horizontal axis shows time, and the vertical axis shows the biomass of P (in blue) and C (in red) vs. time. (C), as in (B), but the vertical axis shows the concentration of glucose (grey), acetate (black) and carbon dioxide (green). (D) Steady state biomass (vertical axis) of the producer strain (P, in blue), consumer strain (C, in red), and both strains (P+C, in black) as a function of the acetate production rate (horizontal axis). This rate is expressed either in absolute flux units (top horizontal axis) or as the percentage of the maximal acetate production rate (bottom horizontal axis), that is, the rate beyond which the producer strain grows so slowly that it is flushed out of the chemostat. (B), (C) and (D) show the results of simulations of ecological dynamics in a chemostat inhabited by an acetate producer strain P and an acetate consumer strain C. For the purpose of these figures, it is assumed that strain C cannot consume glucose (<i>c</i>_{<i>glc</i>,<i>C</i>} = 0). (E) Nutritional niche of the producer strain P (blue) and the consumer strain C (red) when metabolically distinguishable strains coexist. The horizontal and vertical axes show the glucose and acetate consumption rates, respectively, of the indicated strains in metabolic steady-state. P’s steady-state nutrient consumption increases with its acetate production <i>p</i>_{<i>ac</i>,<i>P</i>} (blue arrow). The blend and ratio of nutrients that C consumes varies with the maximal glucose consumption rate <i>c</i>_{<i>glc</i>,<i>C</i>}. That is, increasing C’s maximal glucose consumption <i>c</i>_{<i>glc</i>,<i>C</i>}, increases C’s glucose consumption in steady state while reducing its acetate consumption, as indicated by the red arrow.