The phytopathogenic bacteria Erwinia carotovora infects Drosophila and activates an immune response

Abstract

Although Drosophila possesses potent immune responses, little is known about the microbial pathogens that infect Drosophila . We have identified members of the bacterial genus Erwinia that induce the systemic expression of genes encoding antimicrobial peptides in Drosophila larvae after ingestion. These Erwinia strains are phytopathogens and use flies as vectors; our data suggest that these strains have also evolved mechanisms for exploiting their insect vectors as hosts. Erwinia infections induce an antimicrobial response in Drosophila larvae with a preferential expression of antibacterial versus antifungal peptide-encoding genes. Antibacterial peptide gene expression after Erwinia infection is reduced in two Drosophila mutants that have reduced numbers of hemocytes, suggesting that blood cells play a role in regulating Drosophila antimicrobial responses and also illustrating that this Drosophila – Erwinia interaction provides a powerful model for dissecting host–pathogen relationships.

Nitric oxide contributes to induction of innate immune responses to gram-negative bacteria inDrosophila

“…It has been demonstrated previously that domino mutants are incapable of producing Dipt in their fat body after natural infection with Ecc, whereas fat body production of Drs was not impaired (Basset et al 2000). This result has implicated hemocytes, which are missing in domino mutants, in the response to bacteria; however, as the mutation is relatively pleiotropic, other explanations for the domino dependence are possible.…”

“…These observations led to the proposal that hemocytes may produce a cytokine-like molecule following natural infection that activates antimicrobial peptide production in the fat body (Basset et al 2000). Whereas the proposal that the fat body response is secondary to a hemocyte signal remains tentative because of the pleiotropy of the domino mutation, it is clear that a gut (proventriculus) response can occur independent of hemocytes.…”

“…The trauma of injury weakly activates immune responses even without bacteria, thus eroding the specificity of the response. A recently devised natural infection protocol activated the Imd pathway by briefly feeding larvae on concentrated slurries of a gram-negative bacteria such as Erwinia carotovora carotovora (Ecc; Basset et al 2000).…”

Bacterial strategies to overcome insect defences

“…The proventriculus blockage arises because of hemin storage (hms) gene products 24 , which produce an extracellular matrix that is involved in biofilm formation, both in vitro and in the flea proventriculus 20 30 . The evf (Erwinia virulence factor) gene is required for bacterial persistence 36 .…”

“…A central role in gut tolerance to bacteria has been attributed to amidase PGRPs (PGRP-LB and PGRP-SC) as they abrogate the immunostimulatory activity of peptidoglycan fragments that are released by commensals 46,47 . It is also interesting to note the existence of specialization in the gut epithelium as only parts of the epithelium are immunoreactive, whereas bacteria are present throughout the midgut after infection 18,30,31 .…”