Francisella novicida harbors a divergent type VI secretion system

Francisella tularensis represents an important area of microbiological research due to its status as a tier 1 select agent and its historic use of weaponization and its potential lethality of humans. Under BSL-2 conditions, study of F. tularensis is accomplished using a closely related subspecies, F. novicida which retains virulence in mice, but is attenuated in humans. Pathogenesis of both of these organisms is mediated by a type VI secretion system (TVISS), a relatively recently discovered mechanism of secretion in gram-negative bacteria community based effects in major pathogens such as Pseudomonas aeuroginosa or Vibrio cholerae; unfortunately, little investigation into TVI secretion in divergent bacteria has occured. DNA sequence analysis of F. tularensis vs. F. novicida reveals several additional gene clusters in F. novicida including a TVISS absent from other Francisella species. Characterization of this system could provide insight into the evolution of the genus as a whole, as well as outline the genetic basis for reduce virulence of F. novicida in humans. Here, we attempt to identify and characterize this TVISS through bioinformatic, phenotypic, and direct visual analysis, and illustrate its role in environmental and community interactions.