Abstract
Bacterial sensing, ingestion, and killing by phagocytic cells are essential processes to protect the human body from infectious microorganisms. The cellular mechanisms involved in intracellular killing, their relative importance, and their specificity towards different bacteria are however poorly defined. In this study, we used Dictyostelium discoideum, a phagocytic cell model amenable to genetic analysis, to identify new gene products involved in intracellular killing. A random genetic screen led us to identify the role of Vps13F in intracellular killing of Klebsiella pneumoniae. Vps13F knock‐out (KO) cells exhibited a delayed intracellular killing of K. pneumoniae, although the general organization of the phagocytic and endocytic pathway appeared largely unaffected. Transcriptomic analysis revealed that vps13F KO cells may be functionally similar to previously characterized fspA KO cells, shown to be defective in folate sensing. Indeed, vps13F KO cells showed a decreased chemokinetic response to various stimulants, suggesting a direct or indirect role of Vps13F in intracellular signaling. Overstimulation with excess folate restored efficient killing in vps13F KO cells. Finally, genetic inactivation of Far1, the folate receptor, resulted in inefficient intracellular killing of K. pneumoniae. Together, these observations show that stimulation of Dictyostelium by bacterial folate is necessary for rapid intracellular killing of K. pneumoniae.
Highlights
Phagocytic cells play a key role in the elimination of invading microorganisms in the human body
Phagocytosis is accompanied by a burst in the production of superoxide, and the oxidative burst is thought to play a key role in killing ingested bacteria, because free radicals can react with and damage virtually any biological molecule (Silva, 2010)
We identified Vps13F as a new gene product involved in intracellular killing of K. pneumoniae bacteria by Dictyostelium amoeba
Summary
Phagocytic cells play a key role in the elimination of invading microorganisms in the human body. It has for example been shown that elastase knock‐out mice are highly susceptible to infections with Candida albicans, Klebsiella pneumoniae, and Escherichia coli but not with S. aureus, whereas mice lacking cathepsin G were highly susceptible to S. aureus (Belaaouaj et al, 1998; Reeves et al, 2002) In these mice, microbial killing was abolished despite a normal oxidative burst, suggesting that free radicals and other antimicrobial mechanisms act synergistically, and that their relative importance in the control of infections depends on the infecting pathogen. Detailed analysis revealed that vps13F KO cells are partially defective in bacterial recognition and as a consequence, fail to efficiently kill ingested K. pneumoniae bacteria These results provide the first evidence that over a time scale of a few minutes, recognition of ingested bacteria is necessary to ensure efficient intracellular killing
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