Multifunctional Properties of the Gut Symbiont Enterococcus gallinarum Associated With Eudocima materna Caterpillars...

Gut symbiotic bacteria are highly dynamic and contribute to digestion, development, immunity, detoxification, and environmental adaptation in insect hosts. In fruit-sucking moths (FSM), particularly Eudocima materna (Lepidoptera: Noctuidae), adults are destructive frugivorous pests, whereas larvae feed exclusively on toxic plants such as Tinospora cordifolia. This study investigates the gut bacterial diversity of FSM larvae, with an emphasis on their role in host plant adaptation. Nine bacterial strains were isolated, including Enterobacter hormaechei, Klebsiella aerogenes, Mammaliicoccus sciuri, Staphylococcus sciuri, Staphylococcus aureus, Staphylococcus saprophyticus, and Enterococcus gallinarum. All isolates were subjected to biochemical profiling (sugar and carbohydrate utilization) and antimicrobial susceptibility testing against 12 antibiotics. Among them, E. gallinarum (strain L4), S. sciuri, and M. sciuri exhibited anti-quorum-sensing activity. Notably, E. gallinarum played a key role in host plant digestion and was capable of degrades a ~ 45 kDa protein present in T. cordifolia leaves. GC-MS analysis of methanolic extracts of E. gallinarum revealed several bioactive compounds, including gentamicin A, cyclo (Phe-Pro), isoisopulegol, and gougerotin. Whole-genome sequencing of strain L4 identified genes encoding degradation enzymes (alcohol dehydrogenase, phosphotriesterase), multiple antibiotic resistance genes (YurZ, PptA, CatE, OadB, PycA, and Tdh), diverse metabolic pathways, and secondary metabolite biosynthesis clusters. Subsequently, digestive and detoxification enzymes were identified, including alpha-amylase, serine protease, lipase, chitinase, pectinesterase, carboxylesterase, glutathione peroxidase, and cytochrome P450. Molecular docking analysis showed strong interactions of degradation enzymes with organophosphate insecticides, with binding scores of -6.8 kcal/mol for triazophos and -5.5 kcal/mol for quinalphos. These findings highlight the multifunctional role of E. gallinarum in host plant adaptation and detoxification in FSM larvae, offering new insights into microbe-insect interactions and potential microbial-based biotechnological applications.