Abstract
Microbes produce metabolic resources that are important for cell growth yet leak into the environment. Other microbes can use these resources, adjust their own metabolic production accordingly, and alter the resources available for others. We analyze a model in which metabolite concentrations, production regulation, and population frequencies coevolve in the simple case of two cell types producing two metabolites. We identify three paradoxes where changes that should intuitively benefit a cell type actually harm it. For example, a cell type can become more efficient at producing a metabolite and its relative frequency can decrease—or alternatively the total population growth rate can decrease. Another paradox occurs when a cell type manipulates its counterpart’s production so as to maximize its own instantaneous growth rate, only to achieve a lower final growth rate than had it not manipulated. These paradoxes highlight the complex and counterintuitive dynamics that emerge in simple microbial economies.
Highlights
Microbes produce metabolic resources that are important for cell growth yet leak into the environment
We find that the growth rate is larger than either cell type would have been able to achieve in isolation (Fig. 2a)
We introduce a simple, general mathematical model to understand the interplay between microbial production decisions and population dynamics
Summary
Microbes produce metabolic resources that are important for cell growth yet leak into the environment. A cell type can become more efficient at producing a metabolite and its relative frequency can decrease—or alternatively the total population growth rate can decrease. Another paradox occurs when a cell type manipulates its counterpart’s production so as to maximize its own instantaneous growth rate, only to achieve a lower final growth rate than had it not manipulated. We do not consider punitive goods such as toxins or antibiotics We find it useful to classify goods in terms of which organisms produce them and which organisms benefit from their consumption. One common result of these syntrophic exchanges is a synergy between organisms, where the combined community has enhanced growth relative to any isolated individual[6]
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