Modifying and reacting to the environmental pH can drive bacterial interactions

Abstract

Microbes usually exist in communities consisting of myriad different but interacting species. These interactions are typically mediated through environmental modifications; microbes change the environment by taking up resources and excreting metabolites, which affects the growth of both themselves and also other microbes. We show here that the way microbes modify their environment and react to it sets the interactions within single-species populations and also between different species. A very common environmental modification is a change of the environmental pH. We find experimentally that these pH changes create feedback loops that can determine the fate of bacterial populations; they can either facilitate or inhibit growth, and in extreme cases will cause extinction of the bacterial population. Understanding how single species change the pH and react to these changes allowed us to estimate their pairwise interaction outcomes. Those interactions lead to a set of generic interaction motifs—bistability, successive growth, extended suicide, and stabilization—that may be independent of which environmental parameter is modified and thus may reoccur in different microbial systems.

Author summary

Microbes typically live alongside many other species in complex communities. These microbial communities are very important for us because they also live in and on our bodies and can determine our health and well-being. The composition and function of these communities, such as who is part of such a community and who is excluded, are decided by the interactions between the microbes. These microbial interactions can be driven by many different factors such as resource competition or toxin production. Although these factors are all different, the interactions are typically mediated through the environment; the microbes modify the environment, and they and other microbes have to live in this new environment. We show here that by understanding how microbes change and react to the environment, it is possible to understand and even predict their interactions. We believe that this way of thinking about microbial interactions will lead to a better understanding of more complex communities that are so important for our well-being.