**3.1 Sporulation speculations and beyond**

The best form of dormancy has been studied in gram positive bacteria forming spores. As far as mycobacterium is concerned the existence of spore is debatable. A recent study by a group led jointly by Leif Kirsebom and Santanu Dasgupta in Uppsala University put forward the evidence for existence of spores in mycobacterium (Ghosh et al., 2009). The study revealed existence of endospores in very late stationary phase cultures of *Mycobacterium marinum*, a common model for acute mycobacterial infections. Utilizing transmission electron microscopy the distinct outer coat and cortex of the spores could be identified. Furthermore, heat tolerance, malachite green staining, and the presence of dipicolinic acid was also shown. They were able to isolate rRNA from these sporulating cells and identified it as *M. marinum* rRNA. Extensive bioinformatics analysis identified possible homologues of spore forming genes in mycobacterial genome. Thus they suggested that mycobacteria can form spores under stress and presented the hypothesis that sporulation might be one of the adaptations causing dormancy. When genes encoding GFP or mCherry were introduced on plasmids or integrated in to mycobacterium genome fluorescent spore were seen confirming their mycobacterial origin.

However, a rebuttal to this work by several US labs challenging the concept of endospore formation in mycobacteria was published (Traag et al., 2010) which was responded in to a subsequent rebuttal (Singh et al., 2010). The controversies continue with more supporting evidences yet to be deciphered about a phenomenon not so common to many other species.
