Bacterial-Derived Uracil as a Modulator of Mucosal Immunity and Gut-Microbe Homeostasis in Drosophila

Abstract

All metazoan guts are subjected to immunologically unique conditions in which an efficient antimicrobial system operates to eliminate pathogens while tolerating symbiotic commensal microbiota. However, the molecular mechanisms controlling this process are only partially understood. Here, we show that bacterial-derived uracil acts as a ligand for dual oxidase (DUOX)-dependent reactive oxygen species generation in Drosophila gut and that the uracil production in bacteria causes inflammation in the gut. The acute and controlled uracil-induced immune response is required for efficient elimination of bacteria, intestinal cell repair, and host survival during infection of nonresident species. Among resident gut microbiota, uracil production is absent in symbionts, allowing harmonious colonization without DUOX activation, whereas uracil release from opportunistic pathobionts provokes chronic inflammation. These results reveal that bacteria with distinct abilities to activate uracil-induced gut inflammation, in terms of intensity and duration, act as critical factors that determine homeostasis or pathogenesis in gut-microbe interactions.

The dual oxidase gene BdDuox regulates the intestinal bacterial community homeostasis of Bactrocera dorsalis

“…We hypothesize that the difference in the release of uracil between symbionts and opportunistic pathobionts could explain the difference in BdDuox gene expression described in Figure 2. This is consistent with the observation of Lee et al (2013) that uracil is released primordially by infectious bacteria but not by symbiotic bacteria. It was proposed that free uracil may originate from the breakdown of stable RNA, such as ribosomal RNA, and that uracil release could be considered to an indicator of a specific metabolic and physiological state of the bacterial community (Rinas et al, 1995).…”

“…These results suggest that Duox expression is activated by another mechanism. To date, uracil is the only microbederived factor that modulates Duox activity in Drosophila (Lee et al, 2013). It is possible that BdDuox gene expression is also regulated by uracil in B. dorsalis.…”

Methods to study Drosophila immunity

“…Recently, the group of Won-Jae Lee has employed a novel probe for measuring ROS in Drosophila intestine [101]. This probe (R19S) is a rhodamine-based sensor which specifically reacts with HOCl and not with other ROS [102].…”

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

“…The Drosophila genome contains one DUOX gene, which is indispensable for gut immunity, and an extracellular peroxidase homology domain of DUOX has the enzymatic activity to produce highly microbicidal hypochlorous acid (HOCl) from H 2 O 2 in the presence of chlorine (32). On the other hand, severe gut infection by pathogenic bacteria induces excessive production of DUOX-dependent ROS to damage host tissues and cells and thus decreases the survival rate (11,16). Strains SK1-4 were incubated in the presence of HOCl containing 15 g/liter or 50 g/liter available chlorine to determine the resistance to ROS (Table 6).…”

“…In addition to pathogenic bacteria, commensal microbe-derived peptidoglycans constitutively activate the IMD pathway in the gut through peptidoglycan recognition protein long transcript C and peptidoglycan recognition protein long transcript E, and several types of suppression of the IMD pathway have been reported (10,15). On the other hand, non-commensal bacteria, such as the opportunistic insect pathogen Ecc15 and the insect pathogens Pseudomonas entomophila and Gluconobacter morbifer G707T, secrete uracil to trigger the DUOX-dependent ROS production (16). The IMD pathway-controlled antimicrobial peptides (IMD-AMPs) exhibit a microbicidal effect on a narrow range of virulent bacteria, whereas ROS-based immunity appears to be a more effective antimicrobial system against gut infection (11)(12)(13)(14).…”