Protective role of nanocurcumin against malathion-induced toxicity in selected gut microbiota isolates

The gut microbiota is a diverse and dynamic microbial ecosystem playing a pivotal role in nutrient metabolism, immune regulation, and overall host physiology. Disruption of this microbial balance, or dysbiosis, has been implicated in a range of diseases. Among environmental toxicants, organophosphate pesticides such as malathion are recognized for their potential to alter gut microbial communities; however, the specific effects on probiotic strains have not been fully elucidated. In this study, the influence of malathion on selected probiotic strains — Lactobacillus rhamnosus ( L. rhamnosus) , Lactobacillus plantarum ( L. plantarum) , L. rhamnosus LB21, L. plantarum 299v, and Bacillus coagulans ( B . coagulans )— were evaluated using 2,3,5-triphenyltetrazolium chloride (TTC) assay to assess metabolic activity and colony-forming unit (CFU) assay to measure viability. The malathion exposure resulted in a concentration-dependent decline in both parameters, with L. rhamnosus being the most susceptible. To counteract the observed toxicity, nanocurcumin was synthesized via sonication-assisted process, yielding particles averaging 29 nm in size and exhibiting a zeta potential of –75.8 mV. The antioxidant assays confirmed high radical scavenging activity (IC 50 = 19.91 μg/ml) and ferric reducing capacity of nanocurcumin comparable to that of ascorbic acid. The co-treatment with nanocurcumin significantly improved the viability and metabolic activity of malathion-stressed probiotic strains, particularly L. rhamnosus LB21, which demonstrated substantial recovery. These findings suggest that malathion exerts harmful effects on beneficial gut microbes, and nanocurcumin may serve as a protective and restorative agent to mitigate pesticide-induced microbial dysbiosis. • Malathion caused a concentration-dependent reduction in metabolic activity and viability of selected gut microbiota, with Lactobacillus rhamnosus showing the highest susceptibility. • Bacillus coagulans demonstrated greater tolerance to malathion, indicating species-specific resilience among selected gut microbiota. • Nanocurcumin nanoparticles (∼29 nm, −75.8 mV) exhibited strong stability and potent antioxidant activity, supporting their protective potential. • Nanocurcumin enhanced the metabolic activity of all selected gut microbiota, with the greatest stimulation observed in L. rhamnosus LB21. • Co-treatment with nanocurcumin effectively restored malathion-induced damage in selected gut microbiota, significantly improving TTC activity and CFU counts.