Present address: NYCOMED GmbH, Haidkrugsweg 1, 22885 Willinghusen, Germany.
Expression of the ompATb operon accelerates ammonia secretion and adaptation of Mycobacterium tuberculosis to acidic environments
Article first published online: 16 MAR 2011
© 2011 Blackwell Publishing Ltd
Volume 80, Issue 4, pages 900–918, May 2011
How to Cite
Song, H., Huff, J., Janik, K., Walter, K., Keller, C., Ehlers, S., Bossmann, S. H. and Niederweis, M. (2011), Expression of the ompATb operon accelerates ammonia secretion and adaptation of Mycobacterium tuberculosis to acidic environments. Molecular Microbiology, 80: 900–918. doi: 10.1111/j.1365-2958.2011.07619.x
- Issue published online: 9 MAY 2011
- Article first published online: 16 MAR 2011
- Accepted 24 February, 2011.
Homeostasis of intracellular pH is a trait critical for survival of Mycobacterium tuberculosis in macrophages. However, mechanisms by which M. tuberculosis adapts to acidic environments are poorly understood. In this study, we analysed the physiological functions of OmpATb, a surface-accessible protein of M. tuberculosis. OmpATb did not complement the permeability defects of a Mycobacterium smegmatis porin mutant to glucose, serine and glycerol, in contrast to the porin MspA. Uptake rates of these solutes were unchanged in an ompATb operon mutant of M. tuberculosis indicating that OmpATb is not a general porin. Chemical analysis of low-pH culture filtrates showed that the proteins encoded by the ompATb operon are involved in generating a rapid ammonia burst, which neutralized medium pH and preceded exponential growth of M. tuberculosis. Addition of ammonia accelerated growth of the ompATb operon mutant demonstrating that ammonia secretion is indeed a mechanism by which M. tuberculosis neutralizes acidic environments. Infection experiments revealed that the ompATb operon was not required for full virulence in mice suggesting that M. tuberculosis has multiple mechanisms of resisting phagosomal acidification. Taken together, these results show that the ompATb operon is necessary for rapid ammonia secretion and adaptation of M. tuberculosis to acidic environments in vitro but not in mice.