Porphyrin secretion does not alter heme biosynthesis in the nontuberculous mycobacteria

Both Mycobacterium smegmatis and M. abscessus secrete porphyrin throughout their growth, and other species of bacteria have also been shown to secrete porphyrin with various outcomes. However, how the secretion of a heme precursor alters heme levels remains to be seen. Herein we determined that porphyrin levels and heme levels in the mycobacteria are decoupled as an increase in intracellular or extracellular porphyrin does not alter intracellular heme levels. Our findings support a model for heme biosynthesis with multiple points of regulation, further our understanding of how to alter secretion and buildup of endogenous porphyrins in the mycobacteria, and suggest that mycobacteria have a biological purpose for porphyrin secretion.