The contribution of melanization toDrosophilasurvival changes withEnterococcus faecalisV583 genomic content

Abstract

ABSTRACTEnterococcus faecalisis a human opportunist pathogen able to infect and killDrosophila. Previous studies proved thatE. faecaliscarrying the Fsr quorum sensing system are extremely virulent. Fsr is the regulator of two important virulence factors, gelatinase and serine protease, which cause death ofDrosophilaadult flies by decreasing its tolerance to infection. The exact mechanism underlying the toxicity of theseE. faecalisvirulence factors is nevertheless not known, in particular the way they interfere with the host immune response. In the present study, we investigated the influence of Fsr-GelE-SprE bacterial factors on different immunity responses, namely antimicrobial peptide production, phagocytosis and melanization. UsingE. faecalisV583 wild type andE. faecalisV583 ΔfsrBΔgelEΔsprEmutant we showed that both drosomycin production and phagocytosis were activated to similar levels by the two bacterial strains. However, fly pupae infected with the mutant strain showed less melanization and higher survival rates when compared to pupae infected with wild type bacteria. Using adult flies carrying thePPO1ΔPPO2Δmutation, we found that absence of melanization had a different impact in survival of the flies when infected with the twoE. faecalisstrains.PPO1Δ,PPO2Δmutant flies were more tolerant toE. faecalisdeprived of its major virulence factors. By showing that the presence of theE. faecalisproteases completely alters the impact of melanization activation onDrosophilatolerance, this study provides new clues on the interactions betweenE. faecalisvirulence factors and the fly´s immune system. Future studies onDrosophilaimmunity should consider the pathogen genomic content.