Figure 6. Alanine and alanine dehydrogenase roles in M. tuberculosis nitrogen metabolism.

(a) Growth of M. tuberculosis on alanine as sole nitrogen source or in combination with a second nitrogen source. (b) Gene expression ratios (qPCR) in different nitrogen sources confirms induction of ald gene in the presence of NH₄⁺-containing medium (lower values in the –N/+N plots). "0" indicates the original condition, "-N" indicates medium without a nitrogen source and "+N" indicates medium with a sole nitrogen source.gdh, glnA1, and ansA genes, encoding glutamate dehydrogenase, glutamine synthetase and asparaginase were used as controls, respectively. SigE (Rv1221) was used as internal standard. Symbol colour represents nitrogen source used. Dashed gray lines are used to indicate fold change. Error bars represent standard deviations from three biological replicates. (c) Growth of M. tuberculosis (WT), ald KO, and complemented strains in selected sole nitrogen sources. (d) Labelling of selected amino acids obtained with parent, ald KO, and complemented strains cultured in NH₄⁺ or Gln as sole nitrogen sources. (e) Growth of M. tuberculosis in single nitrogen sources in the presence of various concentrations of bromo-pyruvate (top panels) or methionine sulfoximine (bottom panels), inhibitors of alanine dehydrogenase and glutamine synthetase, respectively. (f) Reaction catalysed by alanine dehydrogenase and glutamine synthetase and their inhibitors. Data shown are representative of two independent experiments. Error bars are standard error of the mean.