The gut bacterium Stenotrophomonas maltophilia enhances insect resistance to RNA biopesticides and baculoviruses via secreted nucleases

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Insecticidal efficacy relies on the ability of oral pesticides to breach the insect gut barrier and enter either epithelial cells or the hemolymph system. However, the role of gut bacteria in modulating the effectiveness of these insecticides remains largely uninvestigated. This study isolated and characterized a specific bacterial strain, Stenotrophomonas maltophilia Sma2, from the cotton bollworm gut. Sma2 significantly increased cotton bollworm’s resistance to RNA-based biopesticides and baculovirus insecticides. Further investigation revealed that Sma2 contributes to host physiological functions by secreting three extracellular nucleases—EN1, EN2, and EN3—into the bacterial supernatant. Among these, EN3 exhibited potent activity against dsRNA (a key component of RNA biopesticides) and baculoviruses (e.g., nucleopolyhedroviruses) both in vitro and in vivo, contributing to the reduced efficacy of these biopesticides. Moreover, silkworms fed with Sma2 showed significantly enhanced resistance to Bombyx mori nucleopolyhedrovirus (BmNPV), leading to higher survival rates. These results underscore the capacity of gut bacteria, such as Sma2, to mediate host antiviral defense, suggesting that commensal bacteria play a crucial role in protecting hosts from viral infections. In summary, this study offers new perspectives on utilizing beneficial commensal bacteria to improve the effectiveness of nucleic acid-based pest control strategies.