Expression of a Bacillus subtilis endoglucanase in protease-deficient Bacillus subtilis strains

Three extracellular protease-deficient Bacillus subtilis strains were transformed with the plasmid pCK98 containing the endo-beta-1,4-glucanase (Eng) gene of B. subtilis BSE616. The three transformants, B. subtilis DB 104 (pCK98), WB600 (pCK98) and WB700 (pCK98), produced the same high level of enzyme activity and showed similar patterns of cell growth and enzyme production. When B. subtilis DB 104 (pCK98), a two-extracellular protease deficient strain, was cultured for 22 h, almost all the secreted enzyme was found to be in the completely cleaved form by both activity staining and Western blotting studies. B. subtilis WB600 (pCK98), a six-extracellular protease-deficient strain, produced a partially cleaved form in addition to the intact form of the enzyme, although the degree of internal cleavage of the enzyme was greatly reduced. With B. subtilis WB700 (pCK98), a seven-extracellular protease-deficient strain, almost all the enzyme was produced as the intact uncleaved form. This study illustrates that a role of the Vpr protease is to degrade foreign proteins produced in B. subtilis and WB700 is a suitable expression system for producing the intact form of the Eng and other foreign proteins that may lose at least part of their efficacy due to internal proteolytic cleavage.