Production of pneumolysin, a pneumococcal toxin, in Bacillus subtilis

We have expressed the pneumolysin gene of Streptococcus pneumoniae in Bacillus subtilis, both from its own promoter and as a fusion protein. The level of expression of pneumolysin from its own promoter was low. The protein produced was hemolytically active. A higher level of expression (about 10 micrograms/ml of culture) was achieved when either one of two C-terminal fragments (corresponding to amino acids 265-471 and 55-471, respectively) or the entire coding part of the pneumolysin gene were fused to the promoter and signal sequence-coding region of the alpha-amylase gene of Bacillus amyloliquefaciens. The C-terminal fusion peptides reacted with anti-pneumolysin serum, but were not hemolytically active. In both cases most of the peptide remained cell-associated. When the entire pneumolysin gene was fused to the signal sequence, a hemolytically active form of pneumolysin could be detected, and most of the product was found in a processed form in the culture supernatant. The full-length pneumolysin secreted from B. subtilis was partially purified and used as antigen in an enzyme immunoassay with rabbit anti-pneumolysin serum.