It is the group of non tuberculous mycobacteria forming Group I of Runyon’s Classification of non tuberculous mycobacteria. 

Features:

They do not form pigment when kept in the dark. But when a young culture is exposed to light in the presence of air for one hour and later incubated for 24-28 hours, they produce a yellow orange pigment. Their rate of growth is slow, but is faster than that of Mycobacterium tuberculosis.

Members of photochromogens include M.kansasii, M.marinum, M.simiae.

1. Mycobacterium marinum
2. Swimming pool granuloma
3. Population growth rates
4. Age pyramid