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Journal of Bacteriology, March 2007, p. 1874-1883, Vol. 189, No. 5
0021-9193/07/$08.00+0     doi:10.1128/JB.01333-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The Alternative Sigma Factor {sigma}H Is Required for Toxin Gene Expression by Bacillus anthracis{triangledown}

Maria Hadjifrangiskou, Yahua Chen, and Theresa M. Koehler*

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

Received 22 August 2006/ Accepted 11 December 2006

Expression of the structural genes for the anthrax toxin proteins is coordinately controlled by host-related signals, such as elevated CO2, and the trans-acting positive regulator AtxA. In addition to these requirements, toxin gene expression is under growth phase regulation. The transition state regulator AbrB represses atxA expression to influence toxin synthesis. During the late exponential phase of growth, when AbrB levels begin to decrease, toxin synthesis increases. Here we report that toxin gene expression also requires the presence of sigH, a gene encoding the RNA polymerase sigma factor associated with development in Bacillus subtilis. In the well-studied B. subtilis system, {sigma}H is required for sporulation and other post-exponential-phase processes and is part of a feedback control pathway for abrB expression. Our data indicate that a Bacillus anthracis sigH-null mutant is asporogenous and toxin deficient. Yet the sigma factor is required for toxin gene expression in a manner that is independent of the pathway leading to post-exponential-phase gene expression. {sigma}H positively controls atxA in an AbrB-independent manner. These findings, combined with previous observations, suggest that the steady-state level of atxA expression is critical for optimal toxin gene transcription. We propose a model whereby, under toxin-inducing growth conditions, control of toxin gene expression is fine-tuned by the independent effects of {sigma}H and AbrB on the expression of atxA.

* Corresponding author. Mailing address: Department of Microbiology and Molecular Genetics, University of Texas—Houston 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.

{triangledown} Published ahead of print on 22 December 2006.

Journal of Bacteriology, March 2007, p. 1874-1883, Vol. 189, No. 5
0021-9193/07/$08.00+0     doi:10.1128/JB.01333-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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