Genome-wide DNA microarray analysis of Francisella tularensis strains demonstrates extensive genetic conservation within the species but identifies regions that are unique to the highly virulent F. tularensis subsp. tularensis.
Francisella tularensis is a potent pathogen and a possible bioterrorism agent. Little is known, however, to explain the molecular basis for its virulence and the distinct differences in virulence found between the four recognized subspecies, F. tularensis subsp. tularensis, F. tularensis subsp. mediasiatica, F. tularensis subsp. holarctica, and F. tularensis subsp. novicida. We developed a DNA microarray based on 1,832 clones from a shotgun library used for sequencing of the highly virulent strain F. tularensis subsp. tularensis Schu S4. This allowed a genome-wide analysis of 27 strains representing all four subspecies. Overall, the microarray analysis confirmed a limited genetic variation within the species F. tularensis, and when the strains were compared, at most 3.7% of the probes showed differential hybridization. Cluster analysis of the hybridization data revealed that the causative agents of type A and type B tularemia, i.e., F. tularensis subsp. tularensis and F. tularensis subsp. holarctica, respectively, formed distinct clusters. Despite marked differences in their virulence and geographical origin, a high degree of genomic similarity between strains of F. tularensis subsp. tularensis and F. tularensis subsp. mediasiatica was apparent. Strains from Japan clustered separately, as did strains of F. tularensis subsp. novicida. Eight regions of difference (RD) 0.6 to 11.5 kb in size, altogether comprising 21 open reading frames, were identified that distinguished strains of the moderately virulent subspecies F. tularensis subsp. holarctica and the highly virulent subspecies F. tularensis subsp. tularensis. One of these regions, RD1, allowed for the first time the development of an F. tularensis-specific PCR assay that discriminates each of the four subspecies.
Broekhuijsen
Martien
M
TNO Prins Maurits Laboratory, Rijswijk, The Netherlands.
Larsson
Pär
P
Johansson
Anders
A
Byström
Mona
M
Eriksson
Ulla
U
Larsson
Eva
E
Prior
Richard G
RG
Sjöstedt
Anders
A
Titball
Richard W
RW
Forsman
Mats
M
D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D016000:Cluster Analysis; D017124:Conserved Sequence; D005604:Francisella tularensis / Q000145:classification* / Q000235:genetics / Q000472:pathogenicity*; D020869:Gene Expression Profiling; D016680:Genome, Bacterial; D006801:Humans; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods*; D017422:Sequence Analysis, DNA; D014406:Tularemia / Q000382:microbiology; D014774:Virulence
D001426:Bacterial Proteins