Microbial interactions as modular: Implications for ecosystem dynamics and evolution

Microbial communities contribute to numerous processes that profoundly impact planetary and human health. They therefore hold potential for addressing many of today's pressing global challenges. Microbial ecosystems have been studied at many levels, ranging from the molecular processes of individual cells to the emergent properties and functions of the entire collective. One notable complexity of these ecosystems is that microbes are constantly engaged in interactions with their environment and other microbes, which in turn influences not only their own growth but also community function, assembly, and stability. While interactions are very often the subject of contemporary microbiology research, these studies often lack precise, mechanistically rooted characterizations of these interactions. In this article, we propose strategies to overcome such limitations by providing a conceptual framework for describing microbe–microbe interactions and discussing the implications of this framework for the study of microbial communities and their evolution. Starting from basic principles, we build a mechanistic description of microbial interactions that treats each interaction as a series of modular, interconnected subprocesses. We then examine how this modularity shapes microbial communities and their evolution, as well as how this modularity can improve our approaches for characterizing and mathematically modeling microbial ecosystems.