Biochemical and morphological changes in dormant ("Nonculturable") Mycobacterium smegmatis cells

Biochemical and morphological changes have been studied during transition of Mycobacterium smegmatis cells into their dormant ("nonculturable") state. A significant fraction of the population of irreversibly "nonculturable" (NC) cells has a thicker cell wall, condensed cytoplasm, and a decreased number of ribosomes. The lipid contents in the NC cells are lower than in the metabolically active cells, with a relatively decreased amount of phospholipid and neutral lipid. Free mycolic acids, which are abundant in metabolically active cells, were not found in the NC cells. The NC forms are also characterized by decreased respiratory activity on endogenous substrates; however, the respiratory chain enzymes retain their activities in the isolated membranes. Activities of the Krebs cycle and glyoxylate cycle enzymes are markedly decreased. Despite a significant decrease in metabolic activity, NC cells possess membrane potential that seems to provide for reversibility of the NC state of mycobacteria, i.e. their capability of reactivating.