title: Inactivation of the ilvB1 gene in Mycobacterium tuberculosis leads to branched-chain amino acid auxotrophy and attenuation of virulence in mice.
abstract: Acetohydroxyacid synthase (AHAS) is the first enzyme in the branched-chain amino acid biosynthesis pathway in bacteria. Bioinformatics analysis revealed that the Mycobacterium tuberculosis genome contains four genes (ilvB1, ilvB2, ilvG and ilvX) coding for the large catalytic subunit of AHAS, whereas only one gene (ilvN or ilvH) coding for the smaller regulatory subunit of this enzyme was found. In order to understand the physiological role of AHAS in survival of the organism in vitro and in vivo, we inactivated the ilvB1 gene of M. tuberculosis. The mutant strain was found to be auxotrophic for all of the three branched-chain amino acids (isoleucine, leucine and valine), when grown with either C(6) or C(2) carbon sources, suggesting that the ilvB1 gene product is the major AHAS in M. tuberculosis. Depletion of these branched chain amino acids in the medium led to loss of viability of the DeltailvB1 strain in vitro, resulting in a 4-log reduction in colony-forming units after 10 days. Survival kinetics of the mutant strain cultured in macrophages maintained with sub-optimal concentrations of the branched-chain amino acids did not show any loss of viability, indicating either that the intracellular environment was rich in these amino acids or that the other AHAS catalytic subunits were functional under these conditions. Furthermore, the growth kinetics of the DeltailvB1 strain in mice indicated that although this mutant strain showed defective growth in vivo, it could persist in the infected mice for a long time, and therefore could be a potential vaccine candidate.
authors: AstraZeneca R&D, Bellary Road, Hebbal, Bangalore-560024, India.
authors: Disha
authors: D
authors: Awasthy
authors: AstraZeneca R&D, Bellary Road, Hebbal, Bangalore-560024, India.
authors: Sheshagiri
authors: S
authors: Gaonkar
authors: AstraZeneca R&D, Bellary Road, Hebbal, Bangalore-560024, India.
authors: R K
authors: RK
authors: Shandil
authors: AstraZeneca R&D, Bellary Road, Hebbal, Bangalore-560024, India.
authors: Reena
authors: R
authors: Yadav
authors: AstraZeneca R&D, Bellary Road, Hebbal, Bangalore-560024, India.
authors: Sowmya
authors: S
authors: Bharath
authors: AstraZeneca R&D, Bellary Road, Hebbal, Bangalore-560024, India.
authors: Nimi
authors: N
authors: Marcel
authors: AstraZeneca R&D, Bellary Road, Hebbal, Bangalore-560024, India.
authors: Venkita
authors: V
authors: Subbulakshmi
authors: AstraZeneca R&D, Bellary Road, Hebbal, Bangalore-560024, India.
authors: Umender
authors: U
authors: Sharma
mesh_terms: D000095:Acetolactate Synthase / Q000172:deficiency / Q000235:genetics; D000597:Amino Acids, Branched-Chain / Q000378:metabolism*; D000818:Animals; D018929:Cell Culture Techniques; D017353:Gene Deletion; D005798:Genes, Bacterial; D008264:Macrophages / Q000382:microbiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009169:Mycobacterium tuberculosis / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity*; D032581:Tuberculosis Vaccines / Q000627:therapeutic use; D014397:Tuberculosis, Pulmonary / Q000382:microbiology* / Q000517:prevention & control; D014613:Vaccines, Attenuated / Q000627:therapeutic use; D014774:Virulence
chemical_list: D000597:Amino Acids, Branched-Chain; D032581:Tuberculosis Vaccines; D014613:Vaccines, Attenuated; D000095:Acetolactate Synthase