RNA Interference Directed against the Transglutaminase Gene Triggers Dysbiosis of Gut Microbiota in Drosophila

Abstract

Edited by Luke O'NeillWe recently reported that transglutaminase (TG) suppresses immune deficiency pathway-controlled antimicrobial peptides (IMD-AMPs), thereby conferring immune tolerance to gut microbes, and that RNAi of the TG gene in flies decreases the lifespan compared with non-TG-RNAi flies. Here, analysis of the bacterial composition of the Drosophila gut by next-generation sequencing revealed that gut microbiota comprising one dominant genus of Acetobacter in non-TG-RNAi flies was shifted to that comprising two dominant genera of Acetobacter and Providencia in TG-RNAi flies. Four bacterial strains, including Acetobacter persici SK1 and Acetobacter indonesiensis SK2, Lactobacillus pentosus SK3, and Providencia rettgeri SK4, were isolated from the midgut of TG-RNAi flies. SK1 exhibited the highest resistance to the IMD-AMPs Cecropin A1 and Diptericin among the isolated bacteria. In contrast, SK4 exhibited considerably lower resistance against Cecropin A1, whereas SK4 exhibited high resistance to hypochlorous acid. The resistance of strains SK1-4 against IMD-AMPs in in vitro assays could not explain the shift of the microbiota in the gut of TGRNAi flies. The lifespan was reduced in gnotobiotic flies that ingested both SK4 and SK1, concomitant with the production of reactive oxygen species and apoptosis in the midgut, whereas the survival rate was not altered in gnotobiotic flies that monoingested either SK4 or SK1. Interestingly, significant amounts of reactive oxygen species were detected in the midgut of gnotobiotic flies that ingested SK4 and SK2, concomitant with no significant apoptosis in the midgut. In gnotobiotic flies that co-ingested SK4 and SK1, an additional unknown factor(s) may be required to cause midgut apoptosis.Foreign substances, including foods, minerals, and microbes, continually pass through the intestinal tract and attach to the gut epithelium. Development of physical and immunologic barriers against foreign substances is thus essential to protect the gut epithelia. Healthy and balanced gut microbiota provide essential nutrients for their host and help to maintain gut immune homeostasis, whereas disruption of the balance, called dysbiosis, is associated with various animal diseases (1, 2). The fruit fly, Drosophila melanogaster, is a useful model for investigating the close relationship between bacteria and bacteria or host and bacteria interactions (3, 4), and the gut microbial community of Drosophila comprises ϳ10 5 microbes of ϳ20 species (5-7). The Drosophila gut is functionally analogous to the mammalian intestinal tract (8, 9), producing antimicrobial peptides (AMPs) 2 and reactive oxygen species (ROS) (10, 11). Microbes or microbe-derived immune elicitors in the fly gut can initiate several immune signaling pathways, such as the immune deficiency (IMD) pathway activated by peptidoglycans to produce AMPs and the dual oxidase (DUOX) signaling pathway activated by uracils to produce . In addition to pathogenic bacteria, commensal microbe-derived peptidoglycans constitutively acti...

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