Repurposing lead, nickel and cadmium resistant Bacillus xiamenensis VITMSJ3 in the effective inhibition of Spodoptera litura larvae: A mechanistic perspective

Abstract

Pests are the major cause for decrease in crop productivity, due to infestation and intense feeding pattern. Use of chemical pesticides not only leads to resistance in pests but can also show residual toxicity. Therefore, in the current study lead, nickel and cadmium resistant Bacillus xiamenensis VITMSJ3 tested as a strong plant growth-promoting bacteria (PGPB) was repurposed for its inhibitory effects against larvae of Spodoptera litura. Toxicity assessment was studied using leaf bioassay against larvae of S. litura and higher mortality rate of 93.33% was attained at 72nd hours upon augmentation with Bacillus xiamenensis VITMSJ3 which was found to be less in B. thuringiensis and pesticide with 83.33 and 53.33% respectively. There was a direct impact with reduction in the feeding of leaves while Bacillus xiamenensis VITMSJ3 was treated with larvae as compared to control with a significant statistical difference at p < 0.05. Histopathological analysis and Scanning Electron Microscopy (SEM) micrographs revealed damage in the gut and breakages in brain. Presence of rod shaped bacteria on the gut surface with morphology similar to Bacillus xiamenensis VITMSJ3 was observed. Further combined plant-larvae study revealed the efficiency of potent PGPR strain to enhance the plant growth inhibiting the survivability of the targeted larvae. Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) enzymatic activities was clearly found higher in plants as compared to larvae. Increased MDA content in larvae inferred the toxic effects of Bacillus xiamenensis VITMSJ3. Similarly the plant infestations and colonization of bacteria was also visualized. Our findings suggests Bacillus xiamenensis VITMSJ3 to be an effective and potential substitute for pest control against larvae of S. litura.