Growth, cell division and sporulation in mycobacteria

Abstract

Bacteria have the ability to adapt to different growth conditions and to survive in various environments. They have also the capacity to enter into dormant states and some bacteria form spores when exposed to stresses such as starvation and oxygen deprivation. Sporulation has been demonstrated in a number of different bacteria but Mycobacterium spp. have been considered to be non-sporulating bacteria. We recently provided evidence that Mycobacterium marinum and likely also Mycobacterium bovis bacillus Calmette-Guérin can form spores. Mycobacterial spores were detected in old cultures and our findings suggest that sporulation might be an adaptation of lifestyle for mycobacteria under stress. Here we will discuss our current understanding of growth, cell division, and sporulation in mycobacteria.

Fig. 1

Mycobacterium marinum spores. a Phase contrast micrograph of vegetative cells, 12 h; endospore, 5d; and spores, 2w. b FM4-64 (membrane dye) stained vegetative cells showing asymmetrical cell division. c Transmission electron micrograph showing the morphological diversity of spores; magnification ×2,000. d Transmission electron micrograph (TEM) of a mature spore; magnification ×60,000. e Scanning electron micrograph (SEM) showing mature spore and vegetative cell. f Malachite green staining for spores, spores appears green. (Space bar = 1 μm). For further details see Ghosh et al. (2009)

Fig. 2

Spores from an old culture (40 days) of the Mycobacterium marinum (strain T CCUG 20998 corresponding to ATCC 927) derivative M. marinum attB::gfp-Kan^R (GFP, green fluorescent protein gene linked to the Kan^R gene integrated into the genome at the L5 attB site, the plasmid was kindly provided by Dr DG Ennis and Ms A. Mallick, Univ of Louisiana, Lafayette, USA) grown in the presence of kanamycin. The two images show phase contrast and fluorescence of the same field as indicated (space bar = 5 μm)