Oversecretion of the Neutral Protease from Bacillus subtilis in Lactococcus lactis spp. lactis JF254

¹ Department of Food Science and Nutrition, University of Minnesota, St. Paul 55108

A thermolytic lactococcal strain that oversecretes neutral protease was constructed. Plasmid profiles and proteolytic activities confirmed that this strain acquired pMG36enpr containing the cloned neutral protease gene from Bacillus subtilis. The oversecreting neutral protease transformant exhibited a halo of white precipitate when it was grown on transparent citrate milk agar and completely solubilized 11% NDM at 21°C after 5 d. Western blot confirmed that the neutral protease halo transformant secreted more neutral protease than did the normal neutral protease transformant. A biochemical and molecular understanding of the mechanism of neutral protease production in the halo transformant could form the basis for the construction of lactococcal strains capable of secreting large amounts of enzymes or other polypeptides that are important to the dairy and food industries.

Key Words: neutral protease • thermolytic • lactococci • ripening

Submitted on August 30, 1993
Accepted on March 7, 1994