PT - JOURNAL ARTICLE AU - Samantha Haller AU - Adrien Franchet AU - Abdul Hakkim AU - Jing Chen AU - Eliana Drenkard AU - Shen Yu AU - Stefanie Schirmeier AU - Zi Li AU - Frederick M. Ausubel AU - Samuel Liégeois AU - Dominique Ferrandon TI - RhlR, but not RhlI, allows <em>P. aeruginosa</em> bacteria to evade <em>Drosophila</em> Tep4-mediated opsonization AID - 10.1101/165530 DP - 2017 Jan 01 TA - bioRxiv PG - 165530 4099 - http://biorxiv.org/content/early/2017/07/26/165530.short 4100 - http://biorxiv.org/content/early/2017/07/26/165530.full AB - When Drosophila flies feed on Pseudomonas aeruginosa strain PA14, some bacteria cross the intestinal barrier and start proliferating inside the hemocoel. This process is limited by hemocytes through phagocytosis. We have previously shown that the PA14 quorum-sensing regulator RhlR is required for these bacteria to elude the cellular immune response. RhlI synthesizes the auto-inducer signal that activates RhlR. Here, we compare the null mutant phenotypes of rhlR and rhlI in a variety of infection assays in Drosophila and in the nematode Caenorhabditis elegans. Surprisingly, in Drosophila, unlike ΔrhlR mutants, ΔrhlI mutants are only modestly attenuated for virulence and are poorly phagocytosed and opsonized in a Thioester-containing Protein4-dependent manner. Likewise, ΔrhlI but not ΔrhlR mutants colonize the digestive tract of C. elegans and kill it as efficiently as wild-type PA14. Thus, RhlR has an RhlI-independent function in eluding detection or counter-acting the action of the immune system. In contrast to the intestinal infection model, Tep4 mutant flies are more resistant to PA14 in a septic injury model, which also depends on rhlR. Thus, the Tep4 putative opsonin can either be protective or detrimental to host defense depending on the infection route.