title: Expression of the ompATb operon accelerates ammonia secretion and adaptation of Mycobacterium tuberculosis to acidic environments.
abstract: 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.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, 609 Bevill Biomedical Research Building, 845 19th Street South, Birmingham, AL 35294, USA.
authors.forename: Houhui
authors.initials: H
authors.lastname: Song
authors.forename: Jason
authors.initials: J
authors.lastname: Huff
authors.forename: Katharine
authors.initials: K
authors.lastname: Janik
authors.forename: Kerstin
authors.initials: K
authors.lastname: Walter
authors.forename: Christine
authors.initials: C
authors.lastname: Keller
authors.forename: Stefan
authors.initials: S
authors.lastname: Ehlers
authors.forename: Stefan H
authors.initials: SH
authors.lastname: Bossmann
authors.forename: Michael
authors.initials: M
authors.lastname: Niederweis
mesh_terms: D000143:Acids / Q000737:chemistry; D000222:Adaptation, Physiological; D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008807:Mice, Inbred BALB C; D020102:Mycobacterium smegmatis / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D009876:Operon; D018272:Porins / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D014376:Tuberculosis / Q000382:microbiology
chemical_list: D000143:Acids; D001426:Bacterial Proteins; C113302:OmpATb protein, Mycobacterium tuberculosis; D018272:Porins; D000641:Ammonia