Bacterial immune systems as causes and consequences of microbiome structure.

Attacks from molecular parasites such as mobile genetic elements (MGEs) have driven the evolution of defense systems in bacterial genomes. Yet, despite significant advances in understanding the molecular mechanisms of these bacterial immune systems, we have only a rudimentary understanding of their ecology and evolution. Bacteria exist as part of complex microbiomes, but community ecology and microbiome research has yet to characterize the impacts of interactions between MGEs and defense mechanisms upon the structure, dynamics and evolution of microbiomes. This Essay introduces and discusses the interplay between bacterial community dynamics and bacterial immune systems, speculating about how these reciprocal interactions may shape microbial community structure and function.