a) M. smegmatis , M. abscessus , M. fortuitum subsp. fortuitum , M. chelonae , and M. goodii were patched onto 7H10 agar media (Difco) at pH 7.0, 6.0, 5.5 or 5.0 to determine pigment production. b) M. avium intracellulare and M. avium subsps. avium were patched onto 7H10 agar media at pH 7.0, 6.0, and 5.5 to determine pigment production. c) From left to right: acetone only, M. smegmatis pH 7.0 extracted w/acetone, M. smegmatis pH 6.0 extracted w/acetone, M. smegmatis pH 5.5 extracted with acetone. d) Fluorescence specific activity units of M. smegmatis bearing empty reporter plasmid pFPV27 or the M. smegmatis probable carotenoid promoter upstream of gfp (pCar) at pH 7.0, 6.0 or 5.5.