The tricarboxylic acid cycle is a central metabolic hub in most cells. Virulence functions of bacterial pathogens such as facultative intracellular Salmonella enterica serovar Typhimurium (STM) are closely connected to cellular metabolism. During systematic analyses of mutant strains with defects in TCA cycle, a strain deficient in all fumarase isoforms (ΔfumABC) elicited a unique metabolic profile. Alongside fumarate STM ΔfumABC accumulates intermediates of glycolysis and pentose phosphate pathway. Analyses by metabolomics and proteomics revealed that fumarate accumulation redirects carbon fluxes towards glycogen synthesis due to high (p)ppGpp levels. In addition, we observed reduced abundance of CheY, leading to altered motility and increased phagocytosis of STM by macrophages. Deletion of glycogen synthase restored normal carbon fluxes and phagocytosis, and partially levels of CheY. We propose that utilization of accumulated fumarate as carbon source induces a status similar to exponential to stationary growth phase transition by switching from preferred carbon sources to fumarate, which increases (p)ppGpp levels and thereby glycogen synthesis. Thus, we observed a new form of interplay between metabolism of STM, and cellular functions and virulence.

Blocks in tricarboxylic acid cycle of Salmonella enterica cause global perturbation of carbon storage, motility and host-pathogen-interaction