Biocontrol potential and characterization of cell-free supernatants from Xenorhabdus nematophila: A novel approach to control Tetranychus urticae

Abstract

The two-spotted spider mite (Tetranychus urticae) poses a significant threat to global agriculture due to its wide host range and rapid development of resistance to chemical pesticides. This research explores the acaricidal effects of cell-free supernatant (CFS) derived from Xenorhabdus nematophila, a bacterium that symbiotically associates with Steinernema carpocapsae, against T. urticae. In vitro assessments demonstrated that treatment with X. nematophila CFS at the highest concentration of 10⁹ CFS/mL resulted in complete mortality of adult mites after 72 h. Additionally, in vivo experiments on Lablab purpureus L. plants showed a remarkable 91.0 % reduction in mite populations 14 days after applying a concentration of 10⁸ CFS/mL. To further investigate the chemical composition and mode of action of the CFS, we conducted metabolite profiling and molecular docking studies. Gas chromatography-mass spectrometry (GC-MS) identified a total of 61 metabolites, with fatty acyls constituting the predominant category (49.2%). Notably, 2-octyl-1H-quinolin-4-one was the most abundant compound, exhibiting a peak area of 10.27%. Molecular docking analyses revealed strong binding affinities of this compound with critical T. urticae proteins, including TuAchE (−8.8 kcal/mol), TuGluCl (−6.1 kcal/mol), and TuMETI (−7.7 kcal/mol), indicating potential disruption of essential physiological functions in the mite. Importantly, the CFS demonstrated minimal toxicity to beneficial organisms, such as the predatory mite Neoseiulus longispinosis and honey bees Apis cerana indica, suggesting its safety for non-target species. Overall, our findings highlight the promising role of X. nematophila and its bioactive compounds as effective and environmentally friendly alternatives for managing T. urticae populations, contributing to sustainable agricultural practices.