Role of the extracytoplasmic-function sigma Factor sigmaH in Mycobacterium tuberculosis global gene expression.

Riccardo Manganelli,1,2 Martin I. Voskuil,3 Gary K.Schoolnik,3 Eugenie Dubnau,1 Manuel Gomez,1 Issar Smith,1*

1TB Center, The Public Health Research Institute at the International Center for Public Health, Newark, NJ 07103-3506, USA. 2Sezione di Microbiologia, Dipartimento di Istologia, Microbiologia e Biotecnologie Mediche, Università di Padova, 35121 Padova, Italy.  3Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA

Abstract: Like other bacterial species, Mycobacterium tuberculosis has multiple sigma (sigma) factors encoded in its genome. In previously published work, we and others have shown that mutations in some of these transcriptional activators render M. tuberculosis sensitive to various environmental stresses and, in some cases, cause attenuated virulence phenotypes. In this paper, we characterize a M. tuberculosis mutant lacking the ECF sigma factor sigmaH. This mutant was more sensitive than the wild type to heat shock and to various oxidative stresses, but did not show de-creased ability to grow inside macrophages. Using quantitative reverse transcription-PCR and microarray technology, we have started to define the sigmaH regulon and its involvement in the global regulation of the response to heat shock and the thiol-specific oxidizing agent diamide. We identified 48 genes whose expression increased after exposure of M. tuberculosis to diamide; out of these, 39 were not induced in the sigH mutant, showing their direct or indirect dependence on sigmaH. Some of these genes encode proteins whose predicted function is related to thiol metabolism, such as thioredoxin, thioredoxin reductase and enzymes involved in cysteine and molybdopterine biosynthesis. Other genes under sigmaH control encode transcriptional regulators such as sigB, sigE, and sigH itself.