Regulation of catalase–peroxidase (KatG) expression, isoniazid sensitivity and virulence by furA of Mycobacterium tuberculosis

Abstract

SummaryMycobacterium tuberculosis has two genes for ferric uptake regulator orthologues, one of which, furA, is situated immediately upstream of katG encoding catalase±peroxidase, a major virulence factor that also activates the prodrug isoniazid. This association suggested that furA might regulate katG and other genes involved in pathogenesis. Transcript mapping showed katG to be expressed from a strong promoter, with consensus 210 and 235 elements, preceding furA. No promoter activity was demonstrated downstream of the furA start codon, using different gene reporter systems, indicating that furA and katG are co-transcribed from a common regulatory region. The respective roles of these two genes in the isoniazid susceptibility and virulence of M. tuberculosis were assessed by combinatorial complementation of a D(furA±katG) strain that is heavily attenuated in a mouse model of tuberculosis. In the absence of furA, katG was upregulated, cells became hypersensitive to isoniazid, and full virulence was restored, indicating that furA regulates the transcription of both genes. When furA alone was introduced into the D(furA±katG) mutant, survival in mouse lungs was moderately increased, suggesting that FurA could regulate genes, other than katG, that are involved in pathogenesis. These do not include the oxidative stress genes ahpC and sodA, or those for siderophore production.

Differential Expression of Mycothiol Pathway Genes: Are they Affected by Antituberculosis Drugs?

“…At higher mycobacterial concentrations the bacilli coagulate, making accurate manipulation of the bacteria impossible. The observed inhibition of bacterial growth suggests that both genes are necessary for mycobacterial viability, although the effects are not as dramatic (for possible drug targeting) as was observed for other essential genes such as glutamine synthetase (19). These results correspond with results obtained by Sassetti et al (35) who showed through transposon mutant libraries that mtr (Rv2855) is essential for mycobacterial growth.…”

Role of KatG catalase‐peroxidase in mycobacterial pathogenesis: countering the phagocyte oxidative burst

“…This phenotype is less severe than that described previously for katG-deleted strains of MTB (Li et al, 1998;Pym et al, 2001). The mutants analysed in previous studies (which were selected on INH) contained large chromosomal deletions encompassing katG and flanking genes; loss of additional virulence genes in these mutants might explain why complementation with katG alone was only partially successful.…”

Regulation of inducible peroxide stress responses

“…In Mycobacterium spp., the furA gene is upstream of, and perhaps cotranscribed with, katG and expression is induced by H 2 O 2 (Milano et al, 2001;Pym et al, 2001;Zahrt et al, 2001). Expression of katG is derepressed in a furA mutant, consistent with a role for FurA as a repressor of catalaseperoxidase expression (Pym et al, 2001).…”

“…In Mycobacterium spp., the furA gene is upstream of, and perhaps cotranscribed with, katG and expression is induced by H 2 O 2 (Milano et al, 2001;Pym et al, 2001;Zahrt et al, 2001). Expression of katG is derepressed in a furA mutant, consistent with a role for FurA as a repressor of catalaseperoxidase expression (Pym et al, 2001). In S. coelicolor, the catC catalase-peroxidase is co-transcribed with furA, which serves as a metal-sensing repressor for the furA-catC operon, but this operon does not appear to be inducible by H 2 O 2 (Hahn et al, 2000b).…”