Peptidoglycan recognition protein-triggered induction of Escherichia coli gene in Drosophila melanogaster

Abstract

Interaction between the host and pathogen determines the fate of both organisms during the infectious state. The host is equipped with a battery of immune reactions, while the pathogen displays a variety of mechanisms to compromise host immunity. Although bacteria alter their pattern of gene expression in host organisms, studies to elucidate the mechanism behind this are only in their infancy. We here examined the possibility that host immune proteins directly participate in the change of gene expression in bacteria. Escherichia coli was treated with a mixture of the extracellular region of peptidoglycan recognition protein (PGRP)-LC and the antimicrobial peptide attacin of Drosophila, and subjected to DNA microarray analysis for mRNA repertoire. We identified 133 annotated genes whose mRNA increased after the treatment, and at least four of them were induced in response to PGRP-LC. One such gene, lipoprotein-encoding nlpI, showed a transient increase of mRNA in adult flies depending on PGRP-LC but not PGRP-LE. NlpI-lacking E. coli had a lowered growth rate and/or viability in flies than the parental strain. These results suggest that a host immune receptor triggers a change of gene expression in bacteria simultaneously with their recognition and induction of immune responses.