New Bacillus thuringiensis strain isolated from the gut of Malabari goat is effective against Tetranychus macfarlanei

Abstract

This study illustrates a novel strain (designated as BPU5) of Bacillus thuringiensis (Bt) isolated from the rumen of Malabari goat, capable of producing polymorphic d-endotoxin crystals concomitantly with sporulation in Luria–Bertani medium (LB), and the d-endotoxin was efficient to combat Tetranychus macfarlanei, a devastating mite. Polymorphic d-endotoxin crystals produced were assessed by scanning electron microscopy and monitored its production concomitantly with sporulation in LB with or without sugar supplements. Toxicity of the d-endotoxin was assessed on T. macfarlanei using leaf disc bioassay method. Mortality rate was determined by comparing the survival of mites on the diet (prepared in 10% sucrose and powdered rice husk) containing different concentrations (1–10 mg/ml) of 72-h-old crude pellet (dried mixture of d-endotoxin (17 mg/g pellet), endospores and a few vegetative cells) or control diet with autoclaved pellet. The maximum production (1.39 mg/ml) of d-endotoxin was observed at 72 h in LB. Among the sugars (glucose, sucrose, maltose or lactose) tested as additional carbon source, glucose (8 g/l) enhanced (1.82 mg/ml) the production of d-endotoxin by 30%. The lethal concentration (LC50) required to kill 50% mites was estimated as 8.024 mg/ml. The d-endotoxin produced by B. thuringiensis BPU5 is shown to efficiently combat T. macfarlanei, a devastating mite infesting agricultural fields.