Intercellular signaling among bacteria is well documented, but autocrine signalling is less well known. In a pair of papers, Mukamolova et al. describe a protein called resuscitation-promoting factor (Rpf) that is secreted by Gram-positive bacteria. Rpf awakens dormant Micrococcus luteus cells, which have become nonculturable after reaching stationary phase. Not merely a rescuer, Rpf also acts like a cytokine to maintain the growth of actively replicating cells; if Rpf is washed away, bacterial growth halts. Several bacterial species, including the pathogen Mycobacterium tuberculosis, encode rpf-like genes. Of particular note is the fact that M. tuberculosis is known to persist in a latent state in individuals, with disease reappearing if the host becomes immunocompromised. If latency involves regulation via Rpf, this protein and its as yet unidentified receptor could be attractive drug or vaccine targets. -- CA
Molec. Microbiol. 46, 611; 623 (2002).
