title: Key role for the alternative sigma factor, SigH, in the intracellular life of Mycobacterium avium subsp. paratuberculosis during macrophage stress.
abstract: Mycobacterium avium subsp. paratuberculosis causes Johne's disease, an enteric infection in cattle and other ruminants, greatly afflicting the dairy industry worldwide. Once inside the cell, M. avium subsp. paratuberculosis is known to survive harsh microenvironments, especially those inside activated macrophages. To improve our understanding of M. avium subsp. paratuberculosis pathogenesis, we examined phagosome maturation associated with transcriptional responses of M. avium subsp. paratuberculosis during macrophage infection. Monitoring cellular markers, only live M. avium subsp. paratuberculosis bacilli were able to prevent phagosome maturation and reduce its acidification. On the transcriptional level, over 300 M. avium subsp. paratuberculosis genes were significantly and differentially regulated in both naive and IFN-γ-activated macrophages. These genes include the sigma factor H (sigH) that was shown to be important for M. avium subsp. paratuberculosis survival inside gamma interferon (IFN-γ)-activated bovine macrophages. Interestingly, an sigH-knockout mutant showed increased sensitivity to a sustained level of thiol-specific oxidative stress. Large-scale RNA sequence analysis revealed that a large number of genes belong to the sigH regulon, especially following diamide stress. Genes involved in oxidative stress and virulence were among the induced genes in the sigH regulon with a putative consensus sequence for SigH binding that was recognized in a subset of these genes (n = 30), suggesting direct regulation by SigH. Finally, mice infections showed a significant attenuation of the ΔsigH mutant compared to its parental strain, suggesting a role for sigH in M. avium subsp. paratuberculosis virulence. Such analysis could identify potential targets for further testing as vaccine candidates against Johne's disease.
authors.affiliation: Laboratory of Bacterial Genomics, Department of Pathobiological Sciences, University of Wisconsin-Madison, Madison, Wisconsin, USA.
authors.forename: Pallab
authors.initials: P
authors.lastname: Ghosh
authors.forename: Chia-wei
authors.initials: CW
authors.lastname: Wu
authors.forename: Adel M
authors.initials: AM
authors.lastname: Talaat
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial / Q000235:genetics; D004926:Escherichia coli; D005260:Female; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008264:Macrophages / Q000382:microbiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D016927:Mycobacterium avium subsp. paratuberculosis / Q000472:pathogenicity / Q000502:physiology*; D020102:Mycobacterium smegmatis; D010283:Paratuberculosis / Q000382:microbiology; D010588:Phagosomes / Q000737:chemistry / Q000382:microbiology; D018085:Regulon; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D013047:Specific Pathogen-Free Organisms; D059467:Transcriptome; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; C120328:SigH protein, bacteria; D012808:Sigma Factor