MSMEG_5684 down-regulation in Mycobacterium smegmatis affects its permeability, survival under stress and persistence

Knockout of MRA_1916 in Mycobacterium tuberculosis H37Ra affects its growth, biofilm formation, survival in macrophages and in mice

Mycobacterium tuberculosis H37Ra (Mtb-Ra) ORF MRA_1916 is annotated as a D-amino acid oxidase (DAO). These enzymes perform conversion of d-amino acids to corresponding imino acids followed by conversion into α-keto-acids. In the present study Mtb-Ra recombinants with DAO knockout (KO) and knockout complemented with DAO over-expressing plasmid (KOC) were constructed. The growth studies showed loss of growth of KO in medium containing glycerol as a primary carbon source. Substituting glycerol with acetate or with FBS addition, restored the growth. Growth was also restored in complemented strain (KOC). KO showed increased permeability to hydrophilic dye EtBr and reduced biofilm formation. Also, its survival in macrophages was low. Phagosome maturation studies suggested enhanced colocalization of KO, compared to WT, with lysosomal marker cathepsin D. Also, an increased intensity of Rab5 and iNOS was observed in macrophages infected with KO, compared to WT and KOC. The in vivo survival studies showed no increase in CFU of KO. This is the first study to show functional relevance of DAO encoded by MRA_1916 for Mtb-Ra growth on glycerol, its permeability and biofilm formation. Also, this study clearly demonstrates that DAO deletion leads to Mtb-Ra failing to grow in macrophages and in mice.

Rv2629 Overexpression Delays Mycobacterium smegmatis and Mycobacteria tuberculosis Entry into Log-Phase and Increases Pathogenicity of Mycobacterium smegmatis in Mice

Objective: The aim of the present study was to explore the potential biological role of Rv2629 in Mycobacterium smegmatis and Mycobacterium tuberculosis.Methods: Recombinant wild type and mutant Rv2629 strains were constructed. Rv2629 expression was evaluated by real-time PCR and western blot. Microarray and interaction network analyses were used to identify the gene interactions associated with wild type and mutant Rv2629. Bacterial growth was assessed in Balb/c mice infected with wild type and mutant Rv2629 strains using CFU assay and histological analysis of the organs. Results: Overexpression of Rv2629 could delay the entry of the Mycobacterium tuberculosis cells into the log-phase, while Rv2629 decreased the number of ribosomes and the expression of uridylate kinase in Mycobacterium smegmatis. The Gene Ontology (GO) and pathway analysis indicated that 122 genes correlated with wild type Rv2629, whereas the Rv2629 mutation led to decrease in the ribosome production, oxidative phosphorylation, and virulence in Mycobacterium tuberculosis. Overexpression of Rv2629 slightly enhanced the drug resistance of Mycobacterium smegmatis to antibiotics, and increased its survival and pathogenicity in Balb/c mice. Conclusion: It is suggested that Rv2629 is involved in the survival of the clinical drug-resistant strain via bacterial growth repression and bacterial persistence induction.

Biochemical and functional characterization of MRA_1571 of Mycobacterium tuberculosis H37Ra and effect of its down-regulation on survival in macrophages

Amino acid biosynthesis has emerged as a source of new drug targets as many bacterial strains auxotrophic for amino acids fail to proliferate under in vivo conditions. Branch chain amino acids (BCAAs) are important for Mycobacterium tuberculosis (Mtb) survival and strains deficient in their biosynthesis were attenuated for growth in mice. Threonine dehydratase (IlvA) is a pyridoxal-5-phosphate (PLP) dependent enzyme that catalyzes the first step in isoleucine biosynthesis. The MRA_1571 of Mycobacterium tuberculosis H37Ra (Mtb-Ra), annotated to be coding for IlvA, was cloned, expressed and purified. Purified protein was subsequently used for developing enzyme assay and to study its biochemical properties. Also, E. coli BL21 (DE3) IlvA knockout (E. coli-ΔilvA) was developed and genetically complemented with Mtb-Ra ilvA expression construct (pET32a-ilvA) to make complemented E. coli strain (E. coli-ΔilvA + pET32a-ilvA). The E. coli-ΔilvA showed growth failure in minimal medium but growth restoration was observed in E. coli-ΔilvA + pET32a-ilvA. E. coli-ΔilvA growth was also restored in the presence of isoleucine. The IlvA localization studies detected its distribution in cell wall and membrane fractions with relatively minor presence in cytosolic fraction. Maximum IlvA expression was observed at 72 h in wild-type (WT) Mtb-Ra infecting macrophages. Also, Mtb-Ra IlvA knockdown (KD) showed reduced survival in macrophages compared to WT and complemented strain (KDC).