Pigmentation of M. marinum mutants in the presence or absence of light. M. marinum colonies were grown in the dark (left) and then exposed to light for 48 h (right). Wild-type (WT) M. marinum is pigmented only after light exposure. R01, MmR01; R02, MmR02; R03, MmR03; R04, MmR04; W01, MmW01; W03, MmW03; W04, MmW04.