Microbial associations are integral to all eukaryotes. Mutualism, the interaction of two
species for the benefit of both, is an important aspect of microbial associations, with
evidence that multicellular organisms in particular benefit from microbes. However, the
microbe's perspective has largely been ignored, and it is unknown whether most microbial
symbionts benefit from their associations with hosts. It has been presumed that microbial
symbionts receive host-derived nutrients or a competition-free environment with reduced …