The role of competition versus cooperation in microbial community coalescence

Abstract

Microbial communities are ubiquitous in nature. Although processes driving the assembly of these consortia are not yet well understood, new communities frequently emerge when two or more microbial ensembles encounter each other and mix to yield a new functioning aggregation, termed "community coalescence". Despite recent advances in our understanding of coalescence, theoretical work has focused mainly on competition, and more work is necessary to determine role of other common microbial interactions, such as cooperation. In this work, we study the combined effects that competitive and cooperative interactions have in the outcome of coalescence events. We simulate communities with varying levels of each type of interaction using a consumer-resource model with cross-feeding on metabolic by-products. We then perform coalescence simulations and measure interaction levels on the pre- and post-coalescence communities using new metrics of competition and cooperation that we present previously. We find that when both interactions are present, the less competitive community tends to succeed in community coalescence, regardless of its cooperativity, suggesting that minimizing competition is the main driving force of this process. When competition is weak however, simulations show that highly cooperative communities are at a disadvantage in coalescence events, indicating that multi-species invasions tend to intercept cooperative links. Microbial community coalescence is gaining popularity in applied and basic research due to its multiple advantages. In the absence of theory that supports real life observations, here we develop a framework to understand and predict the result of community coalescence events from the perspective of biotic interactions present in the community.

Variation in thermal physiology can drive the temperature-dependence of microbial community richness

“…This contrasts with other explanations of unimodality in thermal responses such as enzyme kinetics ( Kontopoulos et al, 2018 ; Arroyo et al, 2022 ) or the metabolic niche hypothesis ( Clarke and Gaston, 2006 ) which invoke reduced metabolic rates at high temperatures (above the OTR), either because of the inactivation of enzymes or the reduction in number of viable metabolic strategies, to explain the decline in coexisting species. Furthermore, the observed patterns of negative covariance seen in existing data (analysed here; ( Smith et al, 2019, 2021 )) suggest that peaks of richness should occur towards the higher end of the operational temperature ranges (OTRs) of most mesophilic bacteria, a prediction that is consistent with unimodal microbial species temperature-richness relationships observed in the real world ( Milici et al, 2016 ; Sharp et al, 2014 ; Thompson et al, 2017 ). We expect that the mechanism we propose here will be particularly relevant to predicting the temperature-richness relationship in: (i) communities where system dynamics is driven primarily by species interactions (as opposed scenarios where environmental filtering or neutral processes dominate); (ii) environments where species typically experience temperatures within their OTR (arguably the most common scenario on planet Earth); (iii) At scales where trait TPC distributions are relatively constant across communities and thus independent of the local environment.…”

“…Finally, we acknowledge that we have only considered competitive interactions here. Whilst it has been argued that competitive interactions dominate in microbial communities ( Foster and Bell, 2012 ) there has more recently been a recognition of the importance of cooperative interactions that develop through cross-feeding between strains on their metabolic-by-products ( Goldford et al, 2018 ; Marsland et al, 2019 ; Lechón et al, 2021 ). The generalised Lotka-Volterra model we use is inappropriate for modeling the dynamical consequences of cooperative interactions due to their inherently destabilising effects in such systems due to the absence of explicit resource dynamics ( Bunin, 2017 ).…”

“…A key aspect missing from these current explanations is the significant variation that exists in thermal responses of key metabolic traits such as growth and respiration rate across microbial taxa ( Smith et al, 2019, 2021 ; Kontopoulos et al, 2020 ). This variation is expected to be important in determining the responses of microbial communities to temperature through two mechanisms.…”

“…In this paper, we derive a new theory that predicts the response of microbial community richness to temperature while accounting for variation in thermal sensitivity of metabolic traits across populations. We focus on competitive interactions, which strongly limit diversity in microbial communities in particular ( Marsland et al, 2019 ; Goldford et al, 2018 ; Ratzke et al, 2020 ; Lechón et al, 2021 ). Using a general model, we first derive a mathematical expression that links the distribution of population thermal performance curves to the number of species that can feasibly coexist within a community.…”

Whole community invasions and the integration of novel ecosystems

“…[ 62 , 70 – 73 ]) and multi-species invasion, the situations are distinct in part because a non-native invader may have characteristics drastically different than the native population. Recent work has also considered the formation of a community from two parent communities in the context of single trophic level microbial communities; in this context the process is sometimes referred to as coalescence [ 74 – 76 ].…”