Metabolic Integration of Bacterial Endosymbionts through Antimicrobial Peptides.

Antimicrobial peptides (AMPs) are massively produced by eukaryotic hosts during symbiotic interactions with bacteria. Among other roles, these symbiotic AMPs have the capacity to permeabilize symbiont membranes and facilitate metabolite flow across the host-symbiont interface. We propose that an ancestral role of these peptides is to facilitate metabolic exchange between the symbiotic partners through membrane permeabilization. This function may be particularly critical for integration of endosymbiont and host metabolism in interactions involving bacteria with strongly reduced genomes lacking most small metabolite transporters. Moreover, AMPs could have acted in a similar way at the onset of plastid and mitochondrion evolution, after a host cell took up a bacterium and needed to extract nutrients from it in the absence of dedicated solute transporters.