University of Maryland College Park College Park, Maryland
We used Beauveria bassiana and seven strains of Metarhizium that differ in infection strategies, and with LT50’s ranging from 3 to 10 days, to study how individual pathogen genotypes interact with Drosophila. The fastest killing strains had the greatest reproductive capacity on cadavers, irrespective of whether they produce toxins, and induced the earliest and largest Toll immune response, so virulence does not depend on suppressing immunity. Consistent with this, Drosophila’s antifungal peptide drosomycin does not inhibit Metarhizium strains. Disrupting the Toll component Dif only increased susceptibility to Beauveria bassiana and Metarhizium frigidum, whereas flies lacking the immune sensor Persephone succumbed quickly to all pathogen strains, including the very weakly pathogenic M. album. Females of most Drosophila lines are more susceptible to Metarhizium than males, but this sexual dimorphism was lost or reversed with some combinations of pathogens and immune-deficient flies. Using the Agilent Array platform, we showed that many Ma549-responsive genes, affecting immune, physiological and homeostatic responses, require Dif or Persephone, but Persephone dependent transcriptome included additional genes that prevent a hyperimmune response and encode non-self-recognition proteins. Persephone also regulates Hayan that activates cuticular melanization and partially suppresses M. frigidum and B. bassiana but not M. anisopliae, whereas deleting Sp7, the activator of hemolymph phenoloxidases, increased longevity of flies infected with M. frigidum, B. bassiana and M. anisopliae. This study emphasizes that the outcome of an infection depends on factors specific to each pathogen interacting with diverse aspects of host immunity.
