Gene from tropical Bacillus sphaericus encoding a protease closely related to subtilisins from Antarctic bacilli

We undertook to identify the protease(s) involved in the in vivo degradation of the 100 kDa mosquitocidal toxin (Mtx) from Bacillus sphaericus SSII-1 and isolated a B. sphaericus SSII-1 gene flanked upstream by a typical Shine-Dalgarno ribosome binding site and downstream by a strong rho-independent transcription terminator. The predicted ORF encodes a 432 amino acid protein with significant homology throughout its sequence to two subtilisin-like serine proteases from the Antarctic psychrophilic (cold-adapted) bacilli, TA39 and TA41. The predicted N-terminal sequence suggests that the B. sphaericus protease is related to sfericase, a partially characterized serine protease from B. sphaericus. Only B. sphaericus strains which produce Mtx-degrading protease activity harbour the subtilisin-like protease gene, suggesting that this protease may be responsible for or contribute to the degradation of Mtx in B. sphaericus SSII-1. A 36-kDa protease with Mtx-degrading activity and similar properties to sfericase was also purified from sporulated cultures of B. sphaericus SSII-1. Further studies are needed to determine the relationship of this protease to sfericase and to the predicted product of the subtilisin-like serine protease gene.