Which games are growing bacterial populations playing?

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 frequency-dependent 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 frequency-dependent, 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.

Fibroblasts and Alectinib switch the evolutionary games played by non-small cell lung cancer

“…Non-cell-autonomous effects [17] allow fitness to depend on a cell's micro-environmental context, including the frequency of other cell types: growth rates need to be measured in competitive fitness assays over a range of seeding frequencies. Other microscopic experimental systems in which frequency dependent fitness effects have been considered include, but are not limited to: Escherichia coli [21,22], yeast [23,24], bacterial symbionts of hydra [25], breast cancer [17] and pancreatic cancer [26]. Hence, we continued our experiments over a range of initial proportions of resistant and parental cells in mixed cultures for each of the four experimental conditions.…”

“…This is due to the higher explanatory value of linear models and our hope to influence the well-established study of matrix games in microscopic systems. Some good EGT work has recently been done on non-linear games [25,26,30], but this is very little compared to the immense literature on matrix games. More importantly, we think that our focus on matrix games is better viewed not from the perspective of model selection but rather as an operational definition of effective games.…”

“…In EGT, a game is the rule mapping the population's strategy distribution to the fitness of individual strategies. Previous work has considered games like snowdrift [24], stag hunt [25], rock-paper-scissors [21], and public goods [23,26] alongside experiments. Instead, we experimentally operationalize the effective game (see [15,16]) as an assayable hidden variable of a population and its environment.…”

Adaptive dynamics of unstable cancer populations: The canonical equation

“…This leaves our model interesting for the previously discussed specific confined experiments, while not yet complete when trying to study three-dimensional growing tumours. While studying modifications to our formalism, following the work of evolutionary game theory on growing populations (see e.g., Li et al, 2015;Melbinger, Cremer, & Frey, 2010), we have decided to present this basic model as it remains a first step into a comprehensible and qualitative insight for the dynamics of populations able to evolve their mutation probability.…”

The Origin of Mucosal Immunity: Lessons from the Holobiont Hydra

“…and Duganella sp.) that synergistically protect the Hydra host from fungal infection (39, 73). The observed frequency-dependent, nonlinear growth rates indicate that the interactions among these two bacteria in coculture are beyond the simple case of direct pairwise interactions.…”