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Free keywords:
bacterial interactions; frequency-dependent
selection; Lotka–Volterra equations; nonlinear
dynamics; population dynamics
Abstract:
Microbial communities display complex population dynamics, both in frequency
and absolute density. Evolutionary game theory provides a natural
approach to analyse and model this complexity by studying the detailed interactions
among players, including competition and conflict, cooperation and
coexistence. Classic evolutionary game theory models typically assume constant
population size, which often does not hold for microbial populations.
Here, we explicitly take into account population growth with frequencydependent
growth parameters, as observed in our experimental system.
We study the in vitro population dynamics of the two commensal bacteria
(Curvibacter sp. (AEP1.3) and Duganella sp. (C1.2)) that synergistically protect
the metazoan host Hydra vulgaris (AEP) from fungal infection. The frequencydependent,
nonlinear growth rates observed in our experiments indicate that
the interactions among bacteria in co-culture are beyond the simple case of
direct competition or, equivalently, pairwise games. This is in agreement
with the synergistic effect of anti-fungal activity observed in vivo. Our analysis
provides new insight into the minimal degree of complexity needed to appropriately
understand and predict coexistence or extinction events in this kind
of microbial community dynamics. Our approach extends the understanding
of microbial communities and points to novel experiments.
