Effect of clpP disruption on alkaline sensitivity of Bacillus thuringiensis

OBJECTIVE: We compared alkaline tolerance between Bacillus thuringiensis (Bt) and B. subtilis (Bs) and to determine the effect on growth when the clpP gene encoding caseinolytic protease is disrupted after alkaline shock. METHODS: B. thuringiensis HD73 mutant with the deletion of clpP gene was constructed by homologous recombination. The effects of clpP deletion on the growth after alkaline shock, sporulation and germination were analyzed. RESULTS: Bt can recover growth from alkaline shock when the medium pH was between 8.9 and 9.1 whereas that was between 8.2 and 8.4 for Bs. Bt tolerated alkaline more than Bs, leading Bt to adapt in alkaline environment of the midgut as a pathogen of insect. Deletion of clpP gene had no influence on sporulation and germination. The clpP mutant grew slower than Bt HD73 in the LB medium in addition to NaOH of 30 mmol/L. It indicates that the ClpP plays an important role in the alkaline tolerance of Bt strain.