Identification of an orphan response regulator required for the virulence of Francisella spp. and transcription of pathogenicity island genes.
Francisella tularensis is a category A agent of biowarfare/biodefense. Little is known about the regulation of virulence gene expression in Francisella spp. Comparatively few regulatory factors exist in Francisella, including those belonging to two-component systems (TCS). However, orphan members of typical TCS can be identified. To determine if orphan TCS members affect Francisella gene expression, a gene encoding a product with high similarity to the Salmonella PmrA response regulator (FTT1557c/FNU0663.2) was deleted in Francisella novicida (a model organism for F. tularensis). The F. novicida pmrA mutant was defective in survival/growth within human and murine macrophage cell lines and was 100% defective in virulence in mice at a dose of up to 10(8) CFU. In addition, the mutant strain demonstrated increased susceptibility to antimicrobial peptide killing, but no differences were observed between the lipid A of the mutant and the parental strain, as has been observed with pmrA mutants of other microbes. The F. novicida pmrA mutant was 100% protective as a single-dose vaccine when challenge was with 10(6) CFU of F. novicida but did not protect against type A Schu S4 wild-type challenge. DNA microarray analysis identified 65 genes regulated by PmrA. The majority of these genes were located in the region surrounding pmrA or within the Francisella pathogenicity island (FPI). These FPI genes are also regulated by MglA, but MglA does not regulate pmrA, nor does PmrA regulate MglA. Thus, the orphan response regulator PmrA is an important factor in controlling virulence in F. novicida, and a pmrA mutant strain is an effective vaccine against homologous challenge.
Mohapatra
Nrusingh P
NP
Center for Microbial Interface Biology, Department of Molecular Biology, Immunology and Medical Genetics, The Ohio State University, 460 W. 12th Avenue, Columbus, OH 43210-1214, USA.
Soni
Shilpa
S
Bell
Brian L
BL
Warren
Richard
R
Ernst
Robert K
RK
Muszynski
Artur
A
Carlson
Russell W
RW
Gunn
John S
JS
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D001428:Bacterial Vaccines / Q000008:administration & dosage; D002460:Cell Line; D005260:Female; D005603:Francisella / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000472:pathogenicity*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D044404:Genomic Islands / Q000235:genetics* / Q000502:physiology; D016905:Gram-Negative Bacterial Infections / Q000517:prevention & control; D006801:Humans; D008264:Macrophages; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D015398:Signal Transduction; D014774:Virulence
D001426:Bacterial Proteins; D001428:Bacterial Vaccines; C081902:pmrA protein, Bacteria