Thermodynamic constraints on the diversity of microbial ecosystems

Jacob Cook and Robert G. Endres, Life Sciences, Imperial College London, London, United Kingdom, Samraat Pawar, Life Sciences, Imperial College London, Ascot, United Kingdom

Background/Question/Methods
Understanding the key role that microbial ecosystems play in many salient processes, such as carbon cycling
and antibiotic resistance, necessarily requires study of the factors shaping their formation and persistence.
Theoretical approaches to this question have often made use of generalisations of the MacArthur consumer-
resource model. However, this type of model cannot capture thermodynamic effects as reaction reversibility
is not considered. We therefore develop a consumer-resource model utilizing fully reversible reaction kinetics.

Results/Conclusions
Using this model, we find ecosystem diversity is strongly linked to the free energy of supplied resource, and
the inclusion of strains utilising near-to-equilibrium reactions increases diversity. These effects arise due to
variation in the rate of substrate diversication between conditions. This suggests that our results should be
observed in ecosystems where diversication from an initial substrate occurs. Our results therefore have clear
implications for understanding ecosystem formation in conditions where only a few substrates are supplied.