Mycobacterium smegmatis

Mycobacterium smegmatis is an acid-fast bacterial species in the phylum Actinomycetota and the genus Mycobacterium. It is 3.0 to 5.0 µm long with a bacillus shape and can be stained by Ziehl–Neelsen method and the auramine-rhodamine fluorescent method. It was first reported in November 1884 by Lustgarten, who found a bacillus with the staining appearance of tubercle bacilli in syphilitic chancres. Subsequent to this, Alvarez and Tavel found organisms similar to that described by Lustgarten also in normal genital secretions (smegma). This organism was later named M. smegmatis.

Some species of the genus Mycobacterium have recently been renamed to Mycolicibacterium, so that M. smegmatis is now Mycolicibacterium smegmatis.

M. smegmatis, which was previously considered a nonmotile organism, uses a sliding mechanism that allows it to move around its environment. Henrichsen defines it as, “a kind of surface translocation produced by the expansive forces in a growing culture in combination with special surface properties of the cells resulting in reduced friction between cell and substrate”. Essentially, the bacteria form a single-layered sheet and are able to move slowly together without the use of any extracellular structures, like flagella or pili. Although it hasn’t been determined exactly how this mechanism works, the surface properties of the unique cell wall (Figure 1) of M. smegmatis have been found to play a role. For example, this sliding ability is correlated with the presence of glycopeptidolipids (GLPs) on the outermost part of the cell wall. GLPs are amphiphilic molecules that could potentially decrease surface interactions or create a conditioning film that allows movement. Although the exact role of GLPs in sliding is not known, without them M. smegmatis does not have the ability to translocate.