title: Inactivation of SAM-methyltransferase is the mechanism of attenuation of a historic louse borne typhus vaccine strain.
abstract: Louse borne typhus (also called epidemic typhus) was one of man's major scourges, and epidemics of the disease can be reignited when social, economic, or political systems are disrupted. The fear of a bioterrorist attack using the etiologic agent of typhus, Rickettsia prowazekii, was a reality. An attenuated typhus vaccine, R. prowazekii Madrid E strain, was observed to revert to virulence as demonstrated by isolation of the virulent revertant Evir strain from animals which were inoculated with Madrid E strain. The mechanism of the mutation in R. prowazekii that affects the virulence of the vaccine was not known. We sequenced the genome of the virulent revertant Evir strain and compared its genome sequence with the genome sequences of its parental strain, Madrid E. We found that only a single nucleotide in the entire genome was different between the vaccine strain Madrid E and its virulent revertant strain Evir. The mutation is a single nucleotide insertion in the methyltransferase gene (also known as PR028) in the vaccine strain that inactivated the gene. We also confirmed that the vaccine strain E did not cause fever in guinea pigs and the virulent revertant strain Evir caused fever in guinea pigs. We concluded that a single nucleotide insertion in the methyltransferase gene of R. prowazekii attenuated the R. prowazekii vaccine strain E. This suggested that an irreversible insertion or deletion mutation in the methyl transferase gene of R. prowazekii is required for Madrid E to be considered a safe vaccine.
authors.affiliation: Department of Microbiology, School of Basic Medical Science, Anhui Medical University, Hefei, Anhui, 230032, China; Department of Pathology, University of Texas Medical Branch, Galveston, Texas, 77555-0609, United States of America.
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Jiangsu Provincial Center for Diseases Control and Prevention, Nanjing, Jiangsu, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Wu
authors.affiliation: Department of Genetics, Washington University School of Medicine, St. Louis, MO, 63110, United States of America.
authors.forename: George
authors.initials: G
authors.lastname: Weinstock
authors.affiliation: Department of Pathology, University of Texas Medical Branch, Galveston, Texas, 77555-0609, United States of America.
authors.forename: David H
authors.initials: DH
authors.lastname: Walker
authors.affiliation: Department of Pathology, University of Texas Medical Branch, Galveston, Texas, 77555-0609, United States of America; School of Public Health, Shandong University, Jinan, Shandong, 250012, China.
authors.forename: Xue-Jie
authors.initials: XJ
authors.lastname: Yu
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D004252:DNA Mutational Analysis / Q000379:methods; D016680:Genome, Bacterial; D006168:Guinea Pigs; D006360:Heat-Shock Proteins; D008780:Methyltransferases / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D010446:Peptide Fragments; D012283:Rickettsia prowazekii / Q000201:enzymology / Q000235:genetics / Q000472:pathogenicity*; D014438:Typhus, Epidemic Louse-Borne / Q000382:microbiology / Q000517:prevention & control / Q000662:veterinary*; D014613:Vaccines, Attenuated / Q000235:genetics / Q000378:metabolism; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D006360:Heat-Shock Proteins; D010446:Peptide Fragments; D014613:Vaccines, Attenuated; D037521:Virulence Factors; C063820:SNP nonapeptide; D008780:Methyltransferases