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