Effect of inhibitors of cell envelope synthesis on β‐sitosterol side chain degradation by Mycobacterium sp. NRRL MB 3683

The role of the lipid bilayer and the peptidoglycan of the mycobacterial cell wall in the permeation of β‐sitosterol into the cell and its transformation to androst‐1‐ene‐3,17‐dione (AD) and androsta‐1,4‐diene‐3,17‐dione (ADD) was studied. Specific inhibitors were used at concentrations affecting the biosynthesis of the assumed target structures, but causing only partial cell growth inhibition or exerting no effect on growth. m ‐Fluorophenylalanine and dl‐norleucine which are known to disorganize the biosynthesis of amphipatic components of the outer layer of the lipid bilayer, used at concentrations 250 μg/ml and 400 μg/ml, respectively, increased the formation rate of AD + ADD from 0.3 (control) to 0.7 and 0.8 mg products/g dry weight/h. The disorganization of the underlying mycolyl‐arabinogalactan structure by the action of ethambutol at the concentration 40 μg/ml, at which the cell growth was apparently not affected, caused the decrease of the product formation from 135 mg/1 to 70 mg/1. In the presence of isoniazid (350 μg/ml) only trace amounts of AD accumulated during 48 hours of transformation indicating much lower activity than that of the intact cells. The most effective among the tested inhibitors of peptidoglycan synthesis were glycine (15 mg/ml) and vancomycin (150 μg/ml) which enhanced the transformation activity of the treated cells nearly three times. Increased transformation rate was also obtained by the action of colistin at concentrations ranging from 10 μg/ml to 15 μg/ml.