Bacterial virulence and Fis: adapting regulatory networks to the host environment

•Fis is a global regulator of virulence in pathogenic bacteria.•Fis regulates the transition from the asymptomatic to symptomatic phase in Dickeya dadantii.•Fis helps environment-driven DNA topology transitions in Salmonella enterica.•Fis is involved in the main stages of enterobacterial pathogenesis.

Pathogenic bacteria have to cope with adverse conditions, such as the host environment and host defense reactions. To adapt quickly to environmental changes, pathogens have developed complex regulatory networks that ensure adequate expression of their virulence genes. Recent evidence suggests that Fis, an abundant nucleoid-associated protein transiently produced during early exponential growth, plays a major role in these networks in several pathogenic bacteria. This review focuses on two enterobacteria, Salmonella enterica and Dickeya dadantii, that inhabit distinct ecological niches to illustrate how Fis uses different strategies to coordinate virulence gene expression, depending on the bacterial lifestyle.