Deletion of σB confers RIF sensitivity in M. smegmatis (Msm), M. abscessus (Mab), and M. tuberculosis (Mtb). (a to c) Tenfold serial dilutions of M. smegmatis mc2155, M. abscessus ATCC 19977, M. tuberculosis mc27000, and their respective ΔsigB and complemented strains were grown to an A600 of 0.7 and spotted on Middlebrook 7H10 ADC or OADC containing the indicated concentrations of RIF. Deletion of sigB results in RIF sensitivity in all three strains. The mutant phenotype can be complemented by constitutive expression of the respective sigB gene.