IndividualMycobacterium tuberculosisResuscitation-Promoting Factor Homologues Are Dispensable for Growth In Vitro and In Vivo

Mycobacterium tuberculosispossesses five genes with significant homology to the resuscitation-promoting factor (Rpf) ofMicrococcus luteus. TheM. luteusRpf is a secreted ∼16-kDa protein which restores active growth to cultures ofM. luteusrendered dormant by prolonged incubation in stationary phase. More recently, the Rpf-like proteins ofM. tuberculosishave been shown to stimulate the growth of extended-stationary-phase cultures ofMycobacterium bovisBCG. These data suggest that the Rpf proteins can influence the growth of mycobacteria; however, the studies do not demonstrate specific functions for the various members of this protein family, nor do they assess the function ofM. tuberculosisRpf homologues in vivo. To address these questions, we have disrupted each of the fiverpf-like genes inM. tuberculosisErdman, and analyzed the mutants for their growth in vitro and in vivo. In contrast toM. luteus, for whichrpfis an essential gene, we find that all of theM. tuberculosis rpfdeletion mutant strains are viable; in addition, all show growth kinetics similar to Erdman wild type both in vitro and in mouse organs following aerosol infection. Analysis ofrpfexpression inM. tuberculosiscultures from early log phase through late stationary phase indicates that expression of therpf-like genes is growth phase-dependent, and that the expression patterns of the fiveM. tuberculosis rpfgenes, while overlapping to various degrees, are not uniform. We also provide evidence that mycobacterialrpfgenes are expressed in vivo in the lungs of mice acutely infected with virulentM. tuberculosis.