Methyl-beta-cyclodextrin alters growth, activity and cell envelope features of sterol-transforming mycobacteria.

Modified beta-cyclodextrins have been shown previously to enhance sterol conversion to 4-androstene-3,17-dione (AD) and 1,4-androstadiene-3,17-dione (ADD) by growing Mycobacterium spp. The enhancement effect was mainly attributed to steroid solubilization by the formation of inclusion complexes with modified cyclodextrins. In this work, the influence of randomly methylated beta-cyclodextrin (MCD) on the growth, AD- and ADD-producing activity, cell wall (CW) composition and ultrastructure of sterol-transforming Mycobacterium sp. VKM Ac-1816D was studied. The specific growth rate of the strain on glycerol increased in the presence of MCD (20-100 mM). Washed cells grown in the presence of MCD (20-40 mM) expressed 1.6-fold higher ADD-producing activity than did the cells grown without MCD, and their adhesiveness differed. Electron microscopy showed MCD-mediated CW exfoliation and accumulation of membrane-like structures outside the cells, while preserving cells intact. The analysis of CW composition revealed both a decrease in the proportion of extractable lipids and a considerable shift in fatty acid profile resulting from MCD action. The MCD-mediated enhancement of mycolic and fatty acids content was observed outside the cells. The total secreted protein level rose 2.4-fold, and the extracellular 3-hydroxysteroid oxidase activity 3.2-fold. The composition of the CW polysaccharide was not altered, while the overall proportion of the carbohydrates in the CW of the MCD-exposed mycobacteria increased. The results showed that the multiple mechanisms of MCD-mediated intensification of sterol to AD(D) conversion by mycobacteria include not only solubilization of steroids, but also the increase of CW permeability for both steroids and soluble nutrients, disorganization of the lipid bilayer and the release of steroid-transforming enzymes weakly associated with the CW.