Mortality causes universal changes in microbial community composition

Clare I Abreu,Vilhelm L Andersen Woltz,Jonathan Friedman,Jeff Gore

doi:10.1038/s41467-019-09925-0

Abstract

All organisms are sensitive to the abiotic environment, and a deteriorating environment can cause extinction. However, survival in a multispecies community depends upon interactions, and some species may even be favored by a harsh environment that impairs others, leading to potentially surprising community transitions as environments deteriorate. Here we combine theory and laboratory microcosms to predict how simple microbial communities will change under added mortality, controlled by varying dilution. We find that in a two-species coculture, increasing mortality favors the faster grower, confirming a theoretical prediction. Furthermore, if the slower grower dominates under low mortality, the outcome can reverse as mortality increases. We find that this tradeoff between growth and competitive ability is prevalent at low dilution, causing outcomes to shift dramatically as dilution increases, and that these two-species shifts propagate to simple multispecies communities. Our results argue that a bottom-up approach can provide insight into how communities change under stress.

Highlights

All organisms are sensitive to the abiotic environment, and a deteriorating environment can cause extinction
We report experimental results that expand upon the prior literature regarding the effect of dilution on pairwise outcomes, and we use the pairwise outcomes to develop a predictive understanding of how multispecies community composition changes with increased dilution
At the highest and lowest dilution factors, one species excludes the others at all starting fractions (Pv at low dilution, Enterobacter aerogenes (Ea) at high dilution)

Summary

Introduction

All organisms are sensitive to the abiotic environment, and a deteriorating environment can cause extinction. Instances of such deterioration include antibiotic use on gut microbiota[8], ocean warming in reef communities[9], overfishing in marine ecosystems[10], and habitat loss in human-modified landscapes[11] Such disturbances can affect community structure in several ways, such as allowing for the spread of invasive species[12], causing biodiversity loss and mass extinction[13,14], or altering the interactions between the remaining community members[15,16]. We find that a pervasive tradeoff between growth rate and competitive ability in our system favors slow growers in high-density, low-dilution environments, leading to striking changes in outcomes as mortality increases. Our results highlight that the seemingly complicated states a community adopts across a mortality gradient can be traced back to a predictable pattern in the outcomes of its constituent pairs

Methods

Results

Conclusion