Characterization of the extracellular lipase of Bacillus subtilis and its relationship to a membrane-bound lipase found in a mutant strain.

Abstract

Bacillus subtilis CMK33 is a mutant that is more osmotically fragile than the wild type when it is converted to the protoplast form. The protoplasts of this mutant contain a membrane-bound lipase, which is not found in protoplasts of the wild type. Hydrolysis of the membrane lipid of mutant protoplasts by the lipase is the cause of their fragility. A protein found in the wild type organism specifically inhibits the lipase (Kent, C., and Lennarz, W. J. (1972) Proc. Natl. Acad. Sci. U. S. A. 69, 2793-2797). This paper reports that cultures of both mutant and wild type cells contain an extracellular lipase which accumulates during the logarithmic phase of growth. The extracellular activity appears to be induced by a component of the growth medium. The membrane-bound lipase of the mutant has been partially purified and its properties have been compared to those of the extracellular lipase of the wild type. Their properties and sensitivity to the wild type inhibitor are similar, which suggests that the two molecules are closely related. The subcellular location of the lipase in the mutant has been investigated and compared to the location of the membrane-bound portion of the lipase inhibitor in the wild type. The lipase is located almost exclusively in the cytoplasmic membrane and not in mesosomal vesicles. In contrast, the lipase inhibitor is located in both types of membranes and is more concentrated in mesosomal vesicles. Under appropriate conditions, the appearance of new extracellular lipase activity in mutant cultures is paralleled by the loss of an equivalent amount of lipase activity from protoplasts prepared from the cells. This suggests that the membrane-bound lipase may be an intermediate in the secretion of the extracellular lipase. Because of the mutation in B. subtilis CMK33, which results in the absence of the lipase inhibitor, this intermediate can be found in protoplasts of the mutant, although it is not detectable in the wild type. Consequently, the mutant may be useful in studies of the mechanism of secretion of exoenzymes by Bacilli.