Levansucrase of Bacillus subtilis: Conclusive evidence that its production and export are unrelated to fatty-acid synthesis but modulated by membrane-modifying agents.

Abstract

Cerulenin action was studied in Bacillus subtilis strains which overproduce several exocellular enzymes. Under conditions in which fatty acid synthesis is partially or completely inhibited by the drug cerulenin, we observed that cell growth and endocellular protein synthesis are scarcely affected during an initial phase, whereas the synthesis of two exocellular enzymes, levansucrase and α-amylase, is markedly reduced. However, careful investigation showed that fatty acid synthesis and exocellular protein production are not inhibited in the same range of cerulenin concentration. Moreover, at a drug concentration which completely inhibits fatty acid synthesis both the half-life of levansucrase messenger RNA and the lag time of the induction process of this enzyme in an inducible strain are unmodified. To account for these data we suggest that cerulenin inhibition of exoenzyme synthesis in these B. subtilis strains is the result of its physiochemical interaction with the membrane rather than the result of its interference with intracellular lipid synthesis. This hypothesis is substantiated by the results obtained from the study of the effects of two membrane-modifying agents on B. subtilis exocellular enzyme production: ethanol and dodecanoic acid. These compounds are not metabolized by the cells and they inhibit levansucrase synthesis. Dodecanoic acid affects levansucrase synthesis to the same extent as cerulenin and within the same concentration range but it does not affect the incorporation of acetate into lipids and is reversibly bound to the cells. A quantitative interpretation of the inhibition caused by these three compounds is proposed, based on the hypothesis that they act at the level of the membrane sites of exocellular enzyme synthesis.