Optimal replication and suppression of inflammation by virulent Francisella tularensis is achieved through reprogramming of host glycolysis.

Abstract

Abstract Francisella tularensis (Ft) is a gram negative, facultative intracellular bacterium that is the causative agent of pneumonic tularemia. Inhalation of as a few as 15 organisms can result in lethal infection. The virulence of Ft is attributed to the bacterium’s ability to both evade and suppress the activation of macrophages. However, the mechanisms and bacterial components required for evasion and suppression by Ft are unclear. Activation of macrophages and induction of antimicrobial responses requires a metabolic shift from oxidative phosphorylation to aerobic glycolysis. Thus, we postulated that Ft manipulates host metabolism as a mechanism of virulence. We established that virulent Ft suppresses induction of aerobic glycolysis among infected macrophages. Moreover, utilizing purified capsule and defined capsule mutants, we elucidated a novel role for Ft capsule as a component contributing to this suppression. The requirement for inhibition of host cell glycolysis in Ft pathogenesis was confirmed via direct inhibition of glycolysis using 2-deoxyglucose. Addition of 2-DG to macrophages infected with capsule mutants partially restored the early intracellular survival and replication of these bacteria, and impaired the secretion of pro-inflammatory cytokines that is typical of infection with these mutants. Together, our data demonstrate that manipulation of host metabolism is an important component of Ft pathogenesis and uncovers a previously unappreciated function of bacterial capsule in the virulence of Ft.