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Glutamate Dehydrogenase Is Required by Mycobacterium bovis BCG for Resistance to Cellular Stress.

ABSTRACT: We recently reported on our success to generate deletion mutants of the genes encoding glutamate dehydrogenase (GDH) and glutamine oxoglutarate aminotransferase (GOGAT) in M. bovis BCG, despite their in vitro essentiality in M. tuberculosis. We could use these mutants to delineate the roles of GDH and GOGAT in mycobacterial nitrogen metabolism by using M. bovis BCG as a model for M. tuberculosis specifically. Here, we extended our investigation towards the involvement of GDH and GOGAT in other aspects of M. bovis BCG physiology, including the use of glutamate as a carbon source and resistance to known phagosomal stresses, as well as in survival inside macrophages. We find that gdh is indispensable for the utilization of glutamate as a major carbon source, in low pH environments and when challenged with nitric oxide. On the other hand, the gltBD mutant had increased viability under low pH conditions and was unaffected by a challenge with nitric oxide. Strikingly, GDH was required to sustain M. bovis BCG during infection of both murine RAW 264.7 and bone-marrow derived and macrophages, while GOGAT was not. We conclude that the catabolism of glutamate in slow growing mycobacteria may be a crucial function during infection of macrophage cells and demonstrate a novel requirement for M. bovis BCG GDH in the protection against acidic and nitrosative stress. These results provide strong clues on the role of GDH in intracellular survival of M. tuberculosis, in which the essentiality of the gdh gene complicates knock out studies making the study of the role of this enzyme in pathogenesis difficult.

SUBMITTER: Gallant JL

PROVIDER: S-EPMC4732601 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Glutamate Dehydrogenase Is Required by Mycobacterium bovis BCG for Resistance to Cellular Stress.

Gallant James L JL Viljoen Albertus J AJ van Helden Paul D PD Wiid Ian J F IJ

PloS one 20160129 1

We recently reported on our success to generate deletion mutants of the genes encoding glutamate dehydrogenase (GDH) and glutamine oxoglutarate aminotransferase (GOGAT) in M. bovis BCG, despite their in vitro essentiality in M. tuberculosis. We could use these mutants to delineate the roles of GDH and GOGAT in mycobacterial nitrogen metabolism by using M. bovis BCG as a model for M. tuberculosis specifically. Here, we extended our investigation towards the involvement of GDH and GOGAT in other a ...[more]

PMID: 26824899

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Project description:The live attenuated bacillus Calmette-Guérin (BCG) vaccine for the prevention of disease associated with Mycobacterium tuberculosis was derived from the closely related virulent tubercle bacillus, Mycobacterium bovis. Although the BCG vaccine has been one of the most widely used vaccines in the world for over 40 years, the genetic basis of BCG's attenuation has never been elucidated. We employed subtractive genomic hybridization to identify genetic differences between virulent M. bovis and M. tuberculosis and avirulent BCG. Three distinct genomic regions of difference (designated RD1 to RD3) were found to be deleted from BCG, and the precise junctions and DNA sequence of each deletion were determined. RD3, a 9.3-kb genomic segment present in virulent laboratory strains of M. bovis and M. tuberculosis, was absent from BCG and 84% of virulent clinical isolates. RD2, a 10.7-kb DNA segment containing a novel repetitive element and the previously identified mpt-64 gene, was conserved in all virulent laboratory and clinical tubercle bacilli tested and was deleted only from substrains derived from the original BCG Pasteur strain after 1925. Thus, the RD2 deletion occurred after the original derivation of BCG. RD1, a 9.5-kb DNA segment found to be deleted from all BCG substrains, was conserved in all virulent laboratory and clinical isolates of M. bovis and M. tuberculosis tested. The reintroduction of RD1 into BCG repressed the expression of at least 10 proteins and resulted in a protein expression profile almost identical to that of virulent M. bovis and M. tuberculosis, as determined by two-dimensional gel electrophoresis. These data indicate a role for RD1 in the regulation of multiple genetic loci, suggesting that the loss of virulence by BCG is due to a regulatory mutation. These findings may be applicable to the rational design of a new attenuated tuberculosis vaccine and the development of new diagnostic tests to distinguish BCG vaccination from tuberculosis infection.

Dataset Information

Glutamate Dehydrogenase Is Required by Mycobacterium bovis BCG for Resistance to Cellular Stress.

Publications

Glutamate Dehydrogenase Is Required by Mycobacterium bovis BCG for Resistance to Cellular Stress.

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