title: The conserved hypothetical protein Rv0574c is required for cell wall integrity, stress tolerance, and virulence of Mycobacterium tuberculosis.
abstract: The virulence of Mycobacterium tuberculosis is intimately related to its distinctive cell wall. The biological significance of poly-α-L-glutamine (PLG), a component in the cell wall of virulent mycobacteria, has not been explored adequately. The focus of this study is to investigate the role of a locus, Rv0574c, coding for a polyglutamate synthase-like protein, in the synthesis of poly-α-L-glutamine in the context of mycobacterial virulence. Evaluation of Rv0574c gene expression in M. tuberculosis demonstrated its growth-phase-linked induction with concomitant accumulation of poly-α-L-glutamine in the cell wall. Rv0574c was activated under conditions prevalent in the tubercular granuloma, e.g., hypoxia, nitric oxide, and CO2. For functional characterization, we produced a deletion mutant of the Rv0574c gene by allelic exchange. The mutant produced smaller amounts of poly-α-L-glutamine in the cell wall than did the wild-type bacterium. Additionally, the increased sensitivity of the mutant to antitubercular drugs, SDS, lysozyme, and mechanical stress was accompanied by a drastic reduction in the ability to form biofilm. Growth of the ΔRv0574c strain was normal under in vitro conditions but was retarded in THP-1 macrophages and in the lungs and spleen of BALB/c mice. This was in agreement with histopathology of the lungs showing slow growth and less severe pathology than that of the wild-type strain. In summary, this study demonstrates that the protein encoded by the Rv0574c locus, by virtue of modulating PLG content in the cell wall, helps in maintaining cellular integrity in a hostile host environment. Also, its involvement in protecting the pathogen from host-generated lethal factors contributes to the infectious biology of M. tuberculosis.
authors.affiliation: School of Biotechnology, Jawaharlal Nehru University, New Delhi, India.
authors.forename: Rajni
authors.initials: R
authors.lastname: Garg
authors.affiliation: School of Biotechnology, Jawaharlal Nehru University, New Delhi, India.
authors.forename: Deeksha
authors.initials: D
authors.lastname: Tripathi
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, New Delhi, India.
authors.forename: Sashi
authors.initials: S
authors.lastname: Kant
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, New Delhi, India.
authors.forename: Harish
authors.initials: H
authors.lastname: Chandra
authors.affiliation: School of Biotechnology, Jawaharlal Nehru University, New Delhi, India.
authors.forename: Rakesh
authors.initials: R
authors.lastname: Bhatnagar
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, New Delhi, India nirupamaban@yahoo.com.
authors.forename: Nirupama
authors.initials: N
authors.lastname: Banerjee
mesh_terms: D000818:Animals; D018441:Biofilms / Q000254:growth & development; D002473:Cell Wall / Q000737:chemistry / Q000502:physiology*; D004195:Disease Models, Animal; D005260:Female; D017353:Gene Deletion; D020869:Gene Expression Profiling; D006801:Humans; D008168:Lung / Q000382:microbiology / Q000473:pathology; D008807:Mice, Inbred BALB C; D009000:Monocytes / Q000382:microbiology; D009169:Mycobacterium tuberculosis / Q000166:cytology* / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity; D010453:Peptide Synthases / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D013154:Spleen / Q000382:microbiology; D013312:Stress, Physiological; D014376:Tuberculosis / Q000382:microbiology / Q000473:pathology; D014774:Virulence
chemical_list: D010455:Peptides; C097188:polyglutamine; D010453:Peptide Synthases; C022414:polyglutamyl synthetase