The study of many important intracellular bacterial pathogens requires an understanding of how specific
virulence factors contribute to pathogenesis during the
infection of host cells. This requires tools to dissect gene function, but unfortunately, there is a lack of such tools for research on many difficult-to-study, or understudied, intracellular pathogens.
Riboswitches are
RNA-based genetic control elements that directly modulate gene expression upon
ligand binding. Here we report the application of
theophylline-sensitive synthetic
riboswitches to induce
protein expression in the intracellular pathogen Francisella. We show that this system can be used to activate the bacterial expression of the reporter β-
galactosidase during growth in rich medium. Furthermore, we applied this system to control the expression of
green fluorescent protein during intracellular
infection by the addition of
theophylline directly to infected macrophages. Importantly, we could control the expression of a novel endogenous
protein required for growth under nutrient-limiting conditions and replication in macrophages, FTN_0818.
Riboswitch-mediated control of FTN_0818 rescued the growth of an FTN_0818 mutant in minimal medium and during macrophage
infection. This is the first demonstration of the use of a synthetic
riboswitch to control an endogenous gene required for a virulence trait in an intracellular bacterium. Since this system can be adapted to diverse bacteria, the ability to use
riboswitches to regulate intracellular bacterial gene expression will likely facilitate the in-depth study of the virulence mechanisms of numerous difficult-to-study intracellular pathogens such as Ehrlichia chaffeensis, Anaplasma phagocytophilum, and Orientia tsutsugamushi, as well as future emerging pathogens.
IMPORTANCE: Determining how specific bacterial genes contribute to virulence during the
infection of host cells is critical to understanding how pathogens cause disease. This can be especially challenging with many difficult-to-study intracellular pathogens.
Riboswitches are
RNA-based genetic control elements that can be used to help dissect gene function, especially since they can be used in a broad range of bacteria. We demonstrate the utility of
riboswitches, and for the first time show that
riboswitches can be used to functionally control a bacterial gene that is critical to the ability of a pathogen to cause disease, during intracellular
infection. Since this system can be adapted to diverse bacteria,
riboswitches will likely facilitate the in-depth study of the virulence mechanisms of numerous difficult-to-study intracellular pathogens, as well as future emerging pathogens.