TNO Prins Maurits Laboratory, Rijswijk
Subspecies of the bacterium Francisella tularensis (a class 3 pathogen and potential biological weapon) display a very close phylogenetic relationship, despite showing marked variations in their virulence for mammals and widely different geographical origin. With the aim to develop high-resolution molecular identification to permit the differentiation of the subspecies, a whole-genome DNA microarray was constructed using a shotgun clone library previously used for the sequencing of the highly virulent F. tularensis Schu-S4 strain. This strategy allowed for a selection of a defined subset of clones with known sequences that together yielded close to full coverage of the F. tularensis genome. Using the Francisella DNA microarray and a selection of F. tularensis strains, specific markers were found that can be used for intraspecies identification. The results also indicate a different subspecies division than currently recognized.