The cell envelope structure and properties of Mycobacterium smegmatis mc2155: is there a clue for the unique transformability of the strain?

1 Institut de Pharmacologie et de Biologie Structurale, Unité Mixte de Recherche du Centre National de la Recherche Scientifique et de l'Université Paul Sabatier (UMR5089), Département ‘Mécanismes Moléculaires des Infections Mycobactériennes’, 205 route de Narbonne, 31077 Toulouse cedex 04, France 2 Unidade de Micobactérias, Instituto Nacional de Saúde Dr Ricardo Jorge, Av. Padre Cruz, 1649-016 Lisboa, Portugal Correspondence Gilles Etienne gilles.etienne{at}ipbs.fr Mycobacterium smegmatis is often used as a surrogate host for pathogenic mycobacteria, especially since the isolation of the transformable smooth morphotype strain mc 2 155 from the isogenic rough wild-type strain ATCC 607. Biochemical analysis of the cell envelope components revealed a lack of polar glycolipids, namely the lipooligosaccharides and the polar subfamilies of glycopeptidolipids, in the mc 2 155 strain. In addition, the latter strain differs from its parent by the distribution of various species of glycolipids and phospholipids between the outermost and deeper layers of the cell envelope. The presence of filamentous and rope-like structures at the cell surface of mc 2 155 cells grown in complex media further supported an ultrastructural change in the cell envelope of the mutant. Importantly, a significantly more rapid uptake of the hydrophobic chenodeoxycholate was observed for the mutant compared to wild-type cells. Taken together, these data indicate that the nature of the surface-exposed and envelope constituents is crucial for the surface properties, cell wall permeability and bacterial phenotype, and suggest that the transformable character of the mc 2 155 strain may be in part explained by these profound modifications of its cell envelope. Abbreviations: ATCC, American Type Culture Collection; ept, efficient-plasmid-transformation; GPL, glycopeptidolipid; LOS, lipooligosaccharide; MALDI-TOF, matrix-assisted laser-desorption/ionization-time of flight; PE, phosphatidylethanolamine; PG, phosphatidylglycerol; PI, phosphatidylinositol; PIM, phosphatidylinositolmannoside; SXM, surface-exposed material; TAG, triacylglycerol; TDM, trehalose dimycolate; TMM, trehalose monomycolate