MprF-mediated immune evasion is necessary for Lactiplantibacillus plantarum resilience in the Drosophila gut during inflammation.

Multiple peptide resistance factor (MprF) confers resistance to cationic antimicrobial peptides (AMPs) in several pathogens, thereby enabling evasion of the host immune response. The role of MprF in commensals remains, however, uncharacterized. To close this knowledge gap, we used a common gut commensal of animals, Lactiplantibacillus plantarum, and its natural host, the fruit fly Drosophila melanogaster, as an experimental model to investigate the role of MprF in commensal-host interactions. The L. plantarum ΔmprF mutant that we generated exhibited deficiency in the synthesis of lysyl-phosphatidylglycerol (Lys-PG), resulting in increased negative cell surface charge and increased susceptibility to AMPs. Susceptibility to AMPs had no effect on ΔmprF mutant's ability to colonize guts of uninfected flies. However, we observed significantly reduced abundance of the ΔmprF mutant after infection-induced inflammation in the guts of wild-type flies but not flies lacking AMPs. Additionally, we found that the ΔmprF mutant compared to wild-type L. plantarum induces a stronger intestinal immune response in flies due to the increased release of immunostimulatory peptidoglycan fragments, indicating an important role of MprF in promoting host tolerance to commensals. Our further analysis suggests that MprF-mediated lipoteichoic acid modifications are involved in host immunomodulation. Overall, our results demonstrate that MprF, besides its well-characterized role in pathogen immune evasion and virulence, is also an important commensal resilience factor. Author summary: Commensal microbial communities residing in the host intestine often experience the exposure to host immune effectors triggered by the pathogens during infection. Despite these perturbations, intestinal commensals stably colonize the host, thus exhibiting resilience to inflammation. Here, we used the fruit fly Drosophila melanogaster and its gut commensal, Lactiplantibacillus plantarum, as a model to investigate the role of a specific bacterial gene, multiple peptide resistance factor (MprF), in commensal-host interactions during infection. We generated an L. plantarum ΔmprF mutant and demonstrated susceptibility of this mutant to AMPs and deficiency in the colonization of flies after infection. Importantly, ΔmprF mutant efficiently colonized flies that lack AMPs, demonstrating that MprF-mediated resistance to host AMPs is crucial for commensal persistence during infection. Additionally, we discovered that the ΔmprF mutant induced due to an increased release of cell-wall fragments enhanced immune response in flies as compared to wild-type bacteria. Hence, MprF confers two highly-relevant functions for commensal-host association: AMP resistance and immune evasion. Finally, we showed a role of MprF in regulating LTA size, implying a broader role of MprF in the bacterial physiology then previously appreciated. Collectively, our work shows that AMP resistance via MprF-mediated lipid and LTA modifications is essential for commensal resilience during inflammation. [ABSTRACT FROM AUTHOR]