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Journal of Bacteriology, January 2002, p. 370-380, Vol. 184, No. 2
0021-9193/01/$04.00+0     DOI: 10.1128/JB.184.2.370-380.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Control of Anthrax Toxin Gene Expression by the Transition State Regulator abrB

Elke Saile and Theresa M. Koehler*

Department of Microbiology and Molecular Genetics, The University of Texas-Houston Health Science Center Medical School, Houston, Texas 77030

Received 17 August 2001/ Accepted 16 October 2001

Bacillus anthracis produces the anthrax toxin proteins protective antigen (PA), lethal factor (LF), and edema factor (EF) in a growth phase-dependent manner when cultured in liquid medium. Expression of the toxin genes pagA, lef, and cya peaks in late log phase, and steady-state levels of the toxin proteins are highest during the transition into stationary phase. Here we show that an apparent transition state regulator negatively regulates toxin gene expression. We identified two orthologues of the B. subtilis transition state regulator abrB in the B. anthracis genome: one on the chromosome and one on the 182-kb virulence plasmid pXO1. The orthologue located on the chromosome is predicted to encode a 94-amino-acid protein that is 85% identical to B. subtilis AbrB. The hypothetical protein encoded on pXO1 is 41% identical to B. subtilis AbrB but missing 27 amino acid residues from the amino terminus compared to the B. subtilis protein. Deletion of the pXO1-encoded abrB orthologue did not affect toxin gene expression under the conditions tested. However, a B. anthracis mutant in which the chromosomal abrB gene was deleted expressed pagA earlier and at a higher level than the parent strain. Expression of a transcriptional pagA-lacZ fusion in the abrB mutant was increased up to 20-fold during early exponential growth compared to the parent strain and peaked in mid-exponential rather than late exponential phase. In contrast to the strong effect of abrB on pagA expression, lef-lacZ and cya-lacZ expression during early-log-phase growth was increased only two- to threefold in the abrB null mutant. Western hybridization analysis showed increased PA, LF, and EF synthesis by the mutant. As is true in B. subtilis, the B. anthracis abrB gene is negatively regulated by spo0A. Our findings tie anthrax toxin gene expression to the complex network of postexponential phase adaptive responses that have been well studied in B. subtilis.

* Corresponding author. Mailing address: Department of Microbiology and Molecular Genetics, University of Texas-Houston Health Science Center Medical School, 6431 Fannin St., JFB 1.765, Houston, TX 77030. Phone: (713) 500-5450. Fax: (713) 500-5499. E-mail: Theresa.M.Koehler{at}uth.tmc.edu.

Journal of Bacteriology, January 2002, p. 370-380, Vol. 184, No. 2
0021-9193/01/$04.00+0     DOI: 10.1128/JB.184.2.370-380.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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