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Volume 158, Issue 2

Alanine racemase mutants of require -alanine for growth and are defective for survival in macrophages and mice Free

Abstract

Alanine racemase (Alr) is an essential enzyme in most bacteria; however, some species (e.g. ) can utilize -amino acid transaminase (Dat) to generate -alanine, which renders Alr non-essential. In addition to the conflicting reports on gene knockout of in a recent study concluded that depletion of Alr does not affect the growth of . In order to get an unambiguous answer on the essentiality of Alr in and validate it as a drug target and , we have inactivated the gene of and found that it was not possible to generate an knockout in the absence of a complementing gene copy or -alanine in the growth medium. The growth kinetics of the mutant revealed that requires very low amounts of -alanine (5–10 µg ml) for optimum growth. Survival kinetics of the mutant in the absence of -alanine indicated that depletion of this amino acid results in rapid loss of viability. The mutant was found to be defective for growth in macrophages. Analysis of phenotype in mice suggested that non-availability of -alanine in mice leads to clearance of bacteria followed by stabilization of bacterial number in lungs and spleen. Additionally, reversal of -cycloserine inhibition in the presence of -alanine in suggested that Alr is the primary target of -cycloserine. Thus, Alr of is a valid drug target and inhibition of Alr alone should result in loss of viability and .

  • Received:
  • Accepted:
  • Revised:
  • Published Online:
© 2012 SGM
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2012-02-01
2024-04-24
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Alanine racemase mutants of Mycobacterium tuberculosis require d-alanine for growth and are defective for survival in macrophages and mice
Microbiology 158, 319 (2012); https://doi.org/10.1099/mic.0.054064-0
/content/journal/micro/10.1099/mic.0.054064-0
/content/journal/micro/10.1099/mic.0.054064-0
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