This Article Full Text (PDF) Other Versions of this Article: JB.00487-07v1 189/18/6714    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Pinto, R. Articles by Leyh, T. S. Search for Related Content PubMed PubMed Citation Articles by Pinto, R. Articles by Leyh, T. S.

 Previous Article  |  Next Article 

J. Bacteriol. doi:10.1128/JB.00487-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Sulfite Reduction in Mycobacteria

The Department of Biochemistry, Howard Hughes Medical Institute, Department of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx, New York 10461-1926

^* To whom correspondence should be addressed. Email: leyh{at}aecom.yu.edu.

	Abstract

Mycobacterium tuberculosis places an enormous burden on the welfare of humanity. Its ability to grow and its pathogenicity are linked to sulfur metabolism, which is considered a fertile area for the development of antibiotics particularly because many of the sulfur-acquisition steps in the bacterium are not found in the host. Sulfite reduction is one such mycobacterial-specific step, and is the central focus of this paper. Sulfite reduction in Mycobacterium smegmatis was investigated using a combination of deletion mutagenesis, metabolite screening, complementation and enzymology. The initial-rate parameters for the purified sufite reductase from M. tuberculosis were determined under strict anaerobic condition (k_cat = 1.0 (± 0.1) electrons consumed per second, and K_m(SO^-23) = 27 (± 1) µM), and the enzyme exhibits no detectible turnover of nitrite - which need not be the case in the sulfite/nitrite-reductase family. Deletion of sulfite reductase (sirA, originally misannotated nirA) reveals that it is essential for growth on sulfate or sulfite as sole sulfur sources, and, further, that the nitrite reducing activities of the cell are incapable of reducing sulfite at a rate sufficient to allow growth. Like their nitrite reductase counterparts, sulfite reductases require a siroheme cofactor for catalysis. Rv2393 (renamed che1) resides in the sulfur-reduction operon, and is shown for the first time to encode a ferrocheletase - catalysts that insert Fe²⁺ into siroheme. Deletion of che1 causes cells to grow slowly on metabolites that require sulfite reductase activity. This slow-growth phenotype was ameliorated by optimizing growth conditions for nitrite assimilation, suggesting that the nitrogen and sulfur assimilation overlap at the point of ferrocheletase synthesis and delivery.