Alternative stable states in a model of microbial community limited by multiple essential nutrients

Abstract

Microbial communities routinely have several alternative stable states observed for the same environmental parameters. Sudden and irreversible transitions between these states make external manipulation of these systems more complicated. To better understand the mechanisms and origins of multistability in microbial communities, we introduce and study a model of a microbial ecosystem colonized by multiple specialist species selected from a fixed pool. Growth of each species can be limited by essential nutrients of two types, e.g. carbon and nitrogen, each represented in the environment by multiple metabolites. We demonstrate that our model has an exponentially large number of potential stable states realized for different environmental parameters. Using game theoretical methods adapted from the stable marriage problem we predict all of these states based only on ranked lists of competitive abilities of species for each of the nutrients. We show that for every set of nutrient influxes, several mutually uninvadable stable states are generally feasible and we distinguish them based upon their dynamic stability. We further explore an intricate network of discontinuous transitions (regime shifts) between these alternative states both in the course of community assembly, or upon changes of nutrient influxes.

Regime shifts in a phage-bacterial ecosystem and strategies for its control

“…The negative interactions between these species are 195 mediated by either their co-infecting phages or their shared nutrients. In this respect 196 the mechanism of bistability in our model is similar to that in consumer resource 197 models without phages (4…”

“…C and N) to have different C:N stoichiometries. 207 Regime shifts and multistability are known to occur when competition between 208 species in principle allows for their co-existence, while the differences in stoichiometry 209 make such coexistence dynamically unstable (14,4). This is also true in our model, 210 where bistability between species B 1 and B 2 is possible whenever their co-existence 211 is dynamically unstable.…”

“…Similarly, multistability studied in Refs. (14,4) requires species competing for two 206 types of essential resources (e.g. C and N) to have different C:N stoichiometries.…”

“…(2) for a review), which have been previously modelled 92 in the context of competition for nutrients (5,4) and without phages. In order for a 93 phage-bacterial ecosystem to be in principle capable of bistability, the slow-growing 94 bacterial species needs to produce disproportionately more phages per each unit 95 of consumed nutrient than the fast-growing one:…”

“…In microbial ecosystems (2) these 41 ms Submission Template mSystems Submission Template mSystems Submission Template mSystems Submission Template mSystems Submission Template mSystems Submission Tem transitions are known to be possible when a bacterial species directly produces some 42 metabolic waste products or antibiotics (3) that inhibit the growth of other bacteria. 43 They may also occur when bacterial species compete for several food sources, which 44 they use either in different stoichiometric ratios (4) or in different preferential orders 45 (5). Here we explore a new type of regime shifts caused by interactions between 46 bacteria and phages.…”