Acidochromogenicity is a common characteristic in nontuberculous mycobacteria

BACKGROUND: An acidic environment is something likely encountered by mycobacteria in the environment or in a human host. Previously mycobacterial species had been known to produce carotenoid pigments in response to light or constitutively. RESULTS: We have tested the ability of various mycobacteria to grow on solid agar plates of differing acidity, and have shown that many species of mycobacteria previously thought to not produce pigment are pigmented when exposed to acidic stress. The Mycobacterium smegmatis promoter region upstream of the genes homologous to those of other mycobacterial species known to code for proteins involved in carotenoid biosynthesis was found to be upregulated under acidic stress. CONCLUSIONS: Mycobacterial species can produce pigment in response to conditions not previously known to induce chromogenicity in mycobacteria. In addition many mycobacterial species previously thought to not produce pigment are actually chromogenic under acidic conditions.