Inhibition of Phagocytic Killing of Escherichia coli in Drosophila Hemocytes by RNA Chaperone Hfq

Abstract

An RNA chaperone of Escherichia coli, called host factor required for phage Qβ RNA replication (Hfq), forms a complex with small noncoding RNAs to facilitate their binding to target mRNA for the alteration of translation efficiency and stability. Although the role of Hfq in the virulence and drug resistance of bacteria has been suggested, how this RNA chaperone controls the infectious state remains unknown. In the present study, we addressed this issue using Drosophila melanogaster as a host for bacterial infection. In an assay for abdominal infection using adult flies, an E. coli strain with mutation in hfq was eliminated earlier, whereas flies survived longer compared with infection with a parental strain. The same was true with flies deficient in humoral responses, but the mutant phenotypes were not observed when a fly line with impaired hemocyte phagocytosis was infected. The results from an assay for phagocytosis in vitro revealed that Hfq inhibits the killing of E. coli by Drosophila phagocytes after engulfment. Furthermore, Hfq seemed to exert this action partly through enhancing the expression of σ38, a stress-responsive σ factor that was previously shown to be involved in the inhibition of phagocytic killing of E. coli, by a posttranscriptional mechanism. Our study indicates that the RNA chaperone Hfq contributes to the persistent infection of E. coli by maintaining the expression of bacterial genes, including one coding for σ38, that help bacteria evade host immunity.

Alteration of the phagocytosis and antimicrobial defense of Octodonta nipae (Coleoptera: Chrysomelidae) pupae to Escherichia coli following parasitism by Tetrastichus brontispae (Hymenoptera: Eulophidae)

“…This was accomplished by comparing the number of live E. coli, the phagocytosis, the bacteriostatic activity, and the mRNA expression level of the AMPs reported mainly against E. coli between parasitized and unparasitized pupae after injection of enhanced green fluorescent protein (EGFP)-expressing E. coli. The choice of EGFP-expressing E. coli was based on the advantage of the being visually engulfed (Bicker et al, 2008;Aung et al, 2012), the induction of antimicrobial reaction (Shiratsuchi et al, 2016), and their propagative ability in infected hosts (Aung et al, 2012). Moreover, the practicability of phagocytosis by the injection of EGFP-expressing E. coli in O. nipae pupae had been previously tested before by Meng et al (2016).…”