Patterns of partnership: surveillance and mimicry in host-microbiota mutualisms.

The repertoire of microbial cues monitored by animal and plant tissues encompasses not just molecules but also microbial activities. These include typical pathogen strategies of injuring membranes, degrading cellular material, and scavenging resources. These activities, however, are not exclusive to pathogens. Instead, they characterize the competitive strategies of microbes living in multispecies communities, like those typically found colonizing host tissues. Similar activities are also deployed by host tissues to keep microbes in check. We propose that host surveillance and mimicry of Microbial-Associated Competitive Activities (MACAs), derived from an evolutionary history of living in mixed microbial communities, has shaped contemporary animal and plant tissue programs of defense, repair, metabolism, and development.