Maintenance affects the stability of a two-tiered microbial 'food chain'?

Microbial 'food chains' are fundamentally different from canonical food chains in the sense that the waste products of the organisms on one trophic level are consumed by organisms of the next trophic level rather than the organisms themselves. In the present paper we introduce a generalised model of a two-tiered microbial 'food chain' with feedback inhibition, after applying an appropriate dimensionless transformation, and investigate its stability analytically. We then parameterised the model with consensus values for syntrophic propionate degradation compiled by the IWA Task Group for Mathematical Modelling of Anaerobic Digestion Processes. Consumption of energy for all processes other than growth is called maintenance. In the absence of maintenance and decay the microbial 'food chain' is intrinsically stable, but when decay is included in the description this is not necessarily the case. We point out that this is in analogy to canonical food chains where introduction of maintenance in the description of a stable (equilibrium or limit cycle) predator-prey system generates chaos.