Phylogenetic Analysis and Heterologous Expression of Surface Layer Protein SlpC of Bacillus sphaericus C3-41

Abstract

The surface layer protein encoding genes from five mosquito-pathogenic Bacillus sphaericus isolates were amplified and sequenced. Negative staining of the S-layer protein extracted from the cell wall of wild-type B. sphaericus C3-41 was prepared. It showed a flat-sheet crystal lattice structure. Two genes encoding the entire and N-terminally truncated S-layer protein (slpC and ΔslpC respectively), were ligated into plasmid pET28a and expressed in Escherichia coli. SDS–PAGE revealed that about 130 KD and 110 KD proteins could be expressed in the cytoplasm of recombinant E. coli BL21(pET28a/slpC) and E. coli BL21(pET28a/ΔslpC) respectively. Furthermore, an intracellular sheet-like or fingerprint-shape structure was investigated in two recombinant strains, which expressed SlpC and ΔSlpC protein respectively, by ultrathin microscopy study, but bioassay results suggested that the S-layer protein of wild B. sphaericus C3-41 and recombinant E. coli BL21 (pET28a/slpC) have no direct toxicity against mosquito larvae. These results should provide information for further understanding of the function of S-layer protein of pathogenic B. sphaericus.