Effects of SpoIVA on the formation of spores and crystal protein in Bacillus thuringiensis

Abstract

In addition to forming spores, Bacillus thuringiensis (Bt) 4.0718 can produce toxins, insecticidal crystal protein (ICP) and vegetative insecticidal protein (Vip). The Bt spoIVA was successfully knocked out by gene recombination and was shown to inhibit sporulation. The mutant strain also exhibited significantly decreased growth and crystal formation, which inhibited spore formation and partially reduced the rate of crystal synthesis.The 50 % lethal concentrations (LC50) values of Bt 4.0718, replacement, complementation and multi-copy mutant strains against the fourth larval stage of H. armigera was determined as 5.422, 6.776, 6.223 and 5.018 μg/mL, respectively. A total of 1814 proteins were identified through isobaric tags for relative and absolute protein (iTRAQ), with 41 and 54 up and downregulated proteins observed. Gene ontology enrichment analysis showed that differentially expressed proteins were primarily involved in the biological process and molecular function. Quantitative real-time PCR analysis confirmed that 9 differential expressed genes exhibited a positive correlation between changes at transcriptional and translational levels. The results of this study provide a basis for further studies of the metabolic regulatory network of spores and crystal protein formation. Moreover, they can be used to ecologically safe insecticide of farmland production because the constructed Bt spoIVA mutants did not produce spores.Provides new ideas for the targeted improvement and application of environmentally friendly spore-free strains.