Deletion of kasB in Mycobacterium tuberculosis causes loss of acid-fastness and subclinical latent tuberculosis in immunocompetent mice

doi:10.1073/pnas.0608654104

Deletion of kasB in Mycobacterium tuberculosis causes loss of acid-fastness and subclinical latent tuberculosis in immunocompetent mice

*Howard Hughes Medical Institute and
^†Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461;
^§Department of Host Defense, Osaka City University Graduate School of Medicine, Osaka 545-8585, Japan;
^‖School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom; and
**Laboratoire de Dynamique Moléculaire des Interactions Membranaires, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5539, Université de Montpellier II, 34095 Montpellier Cedex 5, France

Edited by Barry R. Bloom, Harvard School of Public Health, Boston, MA, and approved February 1, 2007 (received for review October 2, 2006)

Abstract

Mycobacterium tuberculosis, the causative agent of tuberculosis, has two distinguishing characteristics: its ability to stain acid-fast and its ability to cause long-term latent infections in humans. Although this distinctive staining characteristic has often been attributed to its lipid-rich cell wall, the specific dye-retaining components were not known. Here we report that targeted deletion of kasB, one of two M. tuberculosis genes encoding distinct β-ketoacyl- acyl carrier protein synthases involved in mycolic acid synthesis, results in loss of acid-fast staining. Biochemical and structural analyses revealed that the ΔkasB mutant strain synthesized mycolates with shorter chain lengths. An additional and unexpected outcome of kasB deletion was the loss of ketomycolic acid trans-cyclopropanation and a drastic reduction in methoxymycolic acid trans-cyclopropanation, activities usually associated with the trans-cyclopropane synthase CmaA2. Although deletion of kasB also markedly altered the colony morphology and abolished classic serpentine growth (cording), the most profound effect of kasB deletion was the ability of the mutant strain to persist in infected immunocompetent mice for up to 600 days without causing disease or mortality. This long-term persistence of ΔkasB represents a model for studying latent M. tuberculosis infections and suggests that this attenuated strain may represent a valuable vaccine candidate against tuberculosis.

Footnotes

^††To whom correspondence should be addressed. E-mail: jacobsw{at}hhmi.org
Author contributions: A.B., J.C., S.A.P., G.S.B., and W.R.J. designed research; A.B., N.F., K.B., S.S.G., L.K., and B.C. performed research; K.K. and W.R.J. contributed new reagents/analytic tools; A.B., N.F., and K.B. analyzed data; and A.B. and W.R.J. wrote the paper.
↵ ^‡Present address: School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
↵ ^¶Present address: School of Medicine, St. George's University, Grenada, West Indies.
The authors declare no conflict of interest.
This article is a PNAS direct submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0608654104/DC1.
Abbreviations:

ACP,

acyl carrier protein;

FASII,

fatty acid synthase II complex;

MA,

mycolic acid;

MAME,

mycolic acid methyl ester;

TB,

tuberculosis;

TDM,

trehalose dimycolate.