Role of Host Cell-Derived Amino Acids in Nutrition of Intracellular Salmonella enterica
The facultative intracellular pathogenSalmonella entericaresides in a specific membrane-bound compartment termed theSalmonella-containing vacuole (SCV). Despite being segregated from access to metabolites in the host cell cytosol,Salmonellais able to efficiently proliferate within the SCV. We set out to unravel the nutritional supply ofSalmonellain the SCV with focus on amino acids. We studied the availability of amino acids by the generation of auxotrophic strains for alanine, asparagine, aspartate, glutamine, and proline in a macrophage cell line (RAW264.7) and an epithelial cell line (HeLa) and examined access to extracellular nutrients for nutrition. Auxotrophies for alanine, asparagine, or proline attenuated intracellular replication in HeLa cells, while aspartate, asparagine, or proline auxotrophies attenuated intracellular replication in RAW264.7 macrophages. The different patterns of intracellular attenuation of alanine- or aspartate-auxotrophic strains support distinct nutritional conditions in HeLa cells and RAW264.7 macrophages. Supplementation of medium with individual amino acids restored the intracellular replication of mutant strains auxotrophic for asparagine, proline, or glutamine. Similarly, a mutant strain deficient in succinate dehydrogenase was complemented by the extracellular addition of succinate. Complementation of the intracellular replication of auxotrophicSalmonellaby external amino acids was possible if bacteria were proficient in the induction ofSalmonella-induced filaments (SIFs) but failed in a SIF-deficient background. We propose that the ability of intracellularSalmonellato redirect host cell vesicular transport provides access of amino acids to auxotrophic strains and, more generally, is essential to continuously supply bacteria within the SCV with nutrients.