The intersection between host-pathogen interactions and metabolism during Vibrio cholerae infection.

Vibrio cholerae (V. cholerae), the etiological agent of cholera, uses cholera toxin (CT) to cause severe diarrheal disease. Cholera is still a significant cause of mortality worldwide with about half of all cholera cases and deaths occurring in children under five. Owing to the lack of cost-effective vaccination and poor vaccine efficacy in children, there is a need for alternative preventative and therapeutic strategies. Recent advances in our knowledge of the interplay between CT-induced disease and host-pathogen metabolism have opened the door for investigating how modulation of intestinal metabolism by V. cholerae during disease impacts host intestinal immunity, the gut microbiota, and pathogen-phage interactions. In this review article, we examine recent progress in our understanding of host-pathogen interactions during V. cholerae infection and discuss future work deciphering how modulation of gut metabolism during cholera intersects these processes to enable successful fecal-oral transmission of the pathogen.

Francisella tularensis Exploits AMPK Activation to Harvest Host-Derived Nutrients Liberated from Host Lipolysis.

Francisella tularensis is a zoonotic, facultative intracellular bacterial pathogen that replicates in a variety of cell types during infection. Following entry into the cell and phagosome escape, the bacterium replicates rapidly in the cytoplasm. F. tularensis intracellular growth depends on the availability of metabolizable essential nutrients to support replication. However, the mechanism by which metabolizable nutrients become available to the bacterium in the intracellular environment is not fully understood. We found that F. tularensis-infected cells had significantly smaller and fewer lipid droplets than uninfected cells. Inhibition of triacylglycerol degradation significantly reduced bacterial growth, whereas inhibition of triacylglycerol formation did not reduce bacterial growth, suggesting that triacylglycerols sequestered within lipid droplets are important nutrient sources for F. tularensis. We found that F. tularensis-infected cells had increased activation of lipolysis and the upstream regulatory protein AMP protein kinase (AMPK). These data suggest that F. tularensis exploits AMPK activation and lipid metabolism to use host-derived nutrients. Finally, we found that AMPK activation is correlated with an increased bacterial burden, which suggests that it is a host-mediated response to nutrient starvation that results from increased bacterial replication. Altogether, we conclude that F. tularensis exploits AMPK activation to access nutrients sequestered in lipid droplets, specifically glycerol and fatty acids, to undergo efficient bacterial replication and cause successful infection.

Bacterial Synchronized Transfer Assays in Bone Marrow Derived Macrophages.

Merocytophagy ("mero", Greek for partial; "cytophagy" for cell eating) is a process by which cells acquire microbes and cytosolic material through phagocytosis of a small portion of neighboring cells upon cell-cell contact. Cell-cell contact dependent transfer events can be assessed through co-incubation of differently labeled cells. With these assays, it is difficult to analyze the recipient cells by microscopy or bacterial burden within only recipient cells. Therefore, we established a synchronized transfer assay that allows for recipient cells to be isolated from donor cells following transfer events at a high purity. Here, we present this assay in context of bacterial infections and cytosolic cellular staining. With this protocol, mechanisms of cell-cell contact dependent transfer events and the events following merocytophagy can easily be investigated.