Role of Gluconeogenesis and the Tricarboxylic Acid Cycle in the Virulence of Salmonella enterica Serovar Typhimurium in BALB/c Mice

Abstract

In Salmonella enterica serovar Typhimurium, the Cra protein (catabolite repressor/activator) regulates utilization of gluconeogenic carbon sources by activating transcription of genes in the gluconeogenic pathway, the glyoxylate bypass, the tricarboxylic acid (TCA) cycle, and electron transport and repressing genes encoding glycolytic enzymes. A serovar Typhimurium SR-11 ⌬cra mutant was recently reported to be avirulent in BALB/c mice via the peroral route, suggesting that gluconeogenesis may be required for virulence. In the present study, specific SR-11 genes in the gluconeogenic pathway were deleted (fbp, glpX, ppsA, and pckA), and the mutants were tested for virulence in BALB/c mice. The data show that SR-11 does not require gluconeogenesis to retain full virulence and suggest that as yet unidentified sugars are utilized by SR-11 for growth during infection of BALB/c mice. The data also suggest that the TCA cycle operates as a full cycle, i.e., a sucCD mutant, which prevents the conversion of succinyl coenzyme A to succinate, and an ⌬sdhCDA mutant, which blocks the conversion of succinate to fumarate, were both attenuated, whereas both an SR-11 ⌬aspA mutant and an SR-11 ⌬frdABC mutant, deficient in the ability to run the reductive branch of the TCA cycle, were fully virulent. Moreover, although it appears that SR-11 replenishes TCA cycle intermediates from substrates present in mouse tissues, fatty acid degradation and the glyoxylate bypass are not required, since an SR-11 ⌬fadD mutant and an SR-11 ⌬aceA mutant were both fully virulent.In sensitive mice, Salmonella enterica serovar Typhimurium causes a systemic, often fatal disease, similar to human typhoid fever (43). After ingestion, serovar Typhimurium survives passage through the acidic environment of the stomach and reaches the terminal ileum where, within 30 min, it invades M cells in the Peyer's patches (22). Within 60 min, the M cells are destroyed and serovar Typhimurium gains access to both adjacent enterocytes and to underlying lymphoid cells in the mesenteric lymph follicles of the Peyer's patches (22,24). Serovar Typhimurium grows logarithmically in Peyer's patches for 2 days (20) and simultaneously disseminates systemically to the liver and spleen, where it grows in macrophages (40, 43). Mice usually become ruffled and lethargic 3 to 5 days post-oral infection and usually die within 7 to 12 days. Despite much work relating to the relevant virulence mechanisms, little is known about the nutrition of serovar Typhimurium during infection.The Cra protein (catabolite repressor/activator) is a regulator of central carbon metabolism in salmonellae and Escherichia coli. Cra is a transcription factor that activates genes encoding key enzymes in the glyoxylate bypass, gluconeogenesis, the tricarboxylic acid (TCA) cycle, and electron transport and represses genes encoding key enzymes in the EmbdenMeyerhof and Entner-Doudoroff pathways (42). It has recently been reported that a cra mutant of serovar Typhimurium SR-11 is totally avirulent and immunogenic in...

Polyamine biosynthesis and transport mechanisms are crucial for fitness and pathogenesis of Streptococcus pneumoniae

“…Recently, a growing body of literature has alluded to the role of basic metabolites and carbon metabolic pathways in the overall growth, fitness and virulence of bacterial pathogens (Barelle et al, 2006;Muñoz-Elías & McKinney, 2005;Naderer et al, 2006;Shelburne et al, 2008;Tchawa Yimga et al, 2006). In this study a similar degree of attenuation was seen for both transport and biosynthesis mutants during nasopharyngeal colonization, suggesting that genetic deficiencies affecting the availability of certain polyamines are equally detrimental to successful mucosal colonization.…”

Bacterial peptide transporters: Messengers of nutrition to virulence

“…This may slow down the growth but does not affect survival and therefore leave little scope for the development of resistance. Metabolism associated genes of pathogens have been consistently linked with virulence of major pathogens, [1][2][3][4][5][6][7][8][9] such as, role of carbon metabolism related pathways like glycolysis 10 and TCA cycle 11 in virulence of Salmonella Typhimurium and requirement of metabolism associated pathways for protection of Mycobacterium tuberculosis from host immune system. 9 Salmonella is even known to modulate host to exploit the limited supply of nutrients.…”

YgfX (CptA) is a multimeric membrane protein that interacts with the succinate dehydrogenase assembly factor SdhE (YgfY)

“…SDH functions by coupling the oxidation of succinate to fumarate with the reduction of ubiquinone, resulting in the donation of electrons to the electron transport chain (Cecchini, 2003). SDH is also a major contributor to the establishment of infections caused by enterobacterial pathogens, such as Escherichia coli and Salmonella (Alteri et al, 2009;Bowden et al, 2010;Mercado-Lubo et al, 2008;Tchawa Yimga et al, 2006).…”