Enhanced Persistence of Insecticidal Crystal Proteins of Bacillus thuringiensis Subsp kurstaki by Transforming the Predominant Phyllosphere Bacterium, Bacillus megaterium

Abstract

The insecticidal crystal proteins (ICP) of Bacillus thuringiensis (Bt) have relatively short persistence when applied as foliar spray. The limited persistence of the ICP on the phyllosphere is mainly due to alkaline pH and UV radiation in the solar spectrum. In this regard, chemical adjutants, plant derived substances such as phenols and flavinoids have been employed to improve the persistence of the ICP. Alternatively, expression of ICP in a predominant phyllosphere bacterium has been shown to be useful in enhancing the persistence of the same. Therefore, Bacillus megaterium, a predominant phyllosphere bacterium of cabbage, was engineered to express the ICP of Bt subsp kurstaki (Btk) through conjugal transfer. A total of seven stable transformants, viz., A3, B3, C3, El, E2, E3 & F were obtained in the above. Among them, B3 was highly toxic to the important pests of cabbage, Plutella xylostella (0.36 ng/cm²) and Crocidoloutia binotalis (1.74 ng/cm²). Additionally, B3 had extended lysis (96 hours) and higher persistence (9 cfu/cm²) as compared to the rest of the transformants and Btk.