Collagenase COlB1 Is A New Virulence Factor Of Cunninghamella Elegans In Bacillus Thuringiensis

Bacillus thuringiensis is an important entomopathogenic bacteria. They can secrete many active substances to facilitate their invasion of the host, which assists them to grow and resist the immune defenses of host. Based on gene-chip data, there are four collagenase genes, we selected a collagenase gene colB1 encoding ColB1 collagenase which contains a zinc metalloprotease conservative sequence, the HEXXH motif. Moreover, collagen is the principally structural component of Cunninghamella elegans. It shows that collagenases degrade proteins from the nematode cuticle, and help in penetration of the host. For this, we think ColB1 may serve as a virulence factor involved in the infection. The objective of this study is to evaluate the function of ColB1 collagenase from Bt and the main research contents and results are as follows:Here, we showed that purified ColB1 protein showed collagenase activity and toxicity against C. elegans. Not only can ColB1 inhibit the growth of nematode, but also inhibit its brood size. When the concentration of ColB1 is 285 μg/mL, the nematode size is about half of the maximum. In addition, deleting colBl collagenase gene can reduce the virulence of Bt against C. elegans. Using GFP to detect the ColB1 promoter activity and the colonization of mutant strain in C. elegans, we could see that colBl promoter expression was sustainable, deletion of colB1 leads to colonization time-delay. Under the light microscope, we could see that ColB1 not only destroyed the cortical layer of C. elegans but also caused the shrinkage of the gut.These data indicated that collagenase ColB1 involved in the involvement of the collagenase gene in the pathogenesis of Bt and helped to understand the role of collagenase between Bt and C.elegans.