RESUMO
A variety of eubacteria, plants, and protozoa can modify membrane lipids by cyclopropanation, which is reported to modulate membrane permeability and fluidity. The ability to cyclopropanate membrane lipids has been associated with resistance to oxidative stress in Mycobacterium tuberculosis, organic solvent stress in Escherichia coli, and acid stress in E. coli and Salmonella. In bacteria, the cfa gene encoding cyclopropane fatty acid (CFA) synthase is induced during the stationary phase of growth. In the present study, we constructed a cfa mutant of Salmonella enterica serovar Typhimurium 14028s (S. Typhimurium) and determined the contribution of CFA-modified lipids to stress resistance and virulence in mice. Cyclopropane fatty acid content was quantified in wild-type and cfa mutant S. Typhimurium. CFA levels in the cfa mutant were greatly reduced compared to CFA levels in the wild type, indicating that CFA synthase is the major enzyme responsible for cyclopropane modification of lipids in Salmonella. S. Typhimurium cfa mutants were more sensitive to extreme acid pH, the protonophore CCCP, and hydrogen peroxide compared to the wild type. In addition, cfa mutants exhibited reduced viability in murine macrophages and could be rescued by the addition of the NADPH phagocyte oxidase inhibitor diphenyleneiodonium (DPI) chloride. S. Typhimurium lacking cfa was also attenuated for virulence in mice. These observations indicate that CFA modification of lipids makes an important contribution to Salmonella virulence.
Assuntos
Ciclopropanos/metabolismo , Ácidos Graxos/metabolismo , Infecções por Salmonella/microbiologia , Salmonella typhimurium/fisiologia , Animais , Fenômenos Fisiológicos Bacterianos , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Vias Biossintéticas , Ciclopropanos/química , Ciclopropanos/farmacologia , Modelos Animais de Doenças , Ácidos Graxos/química , Ácidos Graxos/farmacologia , Concentração de Íons de Hidrogênio , Macrófagos/efeitos dos fármacos , Macrófagos/imunologia , Macrófagos/microbiologia , Camundongos , Viabilidade Microbiana/efeitos dos fármacos , Viabilidade Microbiana/imunologia , Mutação , Estresse Oxidativo , Infecções por Salmonella/imunologia , Infecções por Salmonella/mortalidade , Salmonella typhimurium/efeitos dos fármacos , VirulênciaRESUMO
Nramp1 is a transporter that pumps divalent cations from the vacuoles of phagocytic cells and is associated with the innate resistance of mice to diverse intracellular pathogens. We demonstrate that sitA and mntH, genes encoding high-affinity metal ion uptake systems in Salmonella enterica serovar Typhimurium, are upregulated when Salmonella is internalized by Nramp1-expressing macrophages and play an essential role in systemic infection of congenic Nramp1-expressing mice.