Engineered Enterococcus faecalis disrupts redox homeostasis to suppress Nosema bombycis in Bombyx mori

Nosema bombycis, the causative agent of pébrine disease, is a major pathogen of the economically important silkworm Bombyx mori, resulting in substantial losses in sericulture. While conventional control strategies offer limited efficacy, symbiont-mediated RNA interference (RNAi) has emerged as a sustainable and targeted strategy for disease control. This study investigates the role of gut microbiota in host defense and evaluates the potential of engineered Enterococcus faecalis to inhibit N. bombycis proliferation by disrupting its antioxidant systems. Germ-free and mono-colonized silkworm models were established to assess the effects of core gut symbionts on N. bombycis infection. Among the tested gut microbiota, E. faecalis demonstrated unique protective properties, reducing N. bombycis gene copy number by 83.97% compared to germ-free controls. This protection was associated with the significant upregulation of host ROS-generating enzymes and sustained elevation of gut ROS levels. Accordingly, N. bombycis infection triggers a substantial reorganization of thioredoxin and glutathione systems to counteract host-derived oxidative stress. Nanoparticle-mediated RNAi targeting microsporidian γ-glutamylcysteine synthetase (γ GCS) and thioredoxin reductase (TrxR) genes significantly reduced N. bombycis gene copy number, confirming the critical role of antioxidant mechanisms in N. bombycis invasion. Finally, the engineered E. faecalis successfully colonized the silkworm gut, where it delivered dsRNA targeting the microsporidian redox system to induce RNAi-mediated gene silencing and significantly suppress N. bombycis proliferation. Our findings broaden the understanding of microbial defense mechanisms and offer a sustainable, symbiont-based RNAi strategy for inhibiting microsporidian infection in silkworm.