Date Published: April 22, 2019
Publisher: Public Library of Science
Author(s): Janina Noster, Tzu-Chiao Chao, Nathalie Sander, Marc Schulte, Tatjana Reuter, Nicole Hansmeier, Michael Hensel, Denise M. Monack.
Intracellular Salmonella enterica serovar Typhimurium (STM) deploy the Salmonella Pathogenicity Island 2-encoded type III secretion system (SPI2-T3SS) for the massive remodeling of the endosomal system for host cells. This activity results in formation of an extensive interconnected tubular network of Salmonella-induced filaments (SIFs) connected to the Salmonella-containing vacuole (SCV). Such network is absent in cells infected with SPI2-T3SS-deficient mutant strains such as ΔssaV. A tubular network with reduced dimensions is formed if SPI2-T3SS effector protein SseF is absent. Previous single cell live microscopy-based analyses revealed that intracellular proliferation of STM is directly correlated to the ability to transform the host cell endosomal system into a complex tubular network. This network may also abrogate host defense mechanisms such as delivery of antimicrobial effectors to the SCV. To test the role of SIFs in STM patho-metabolism, we performed quantitative comparative proteomics of STM recovered from infected murine macrophages. We infected RAW264.7 cells with STM wild type (WT), ΔsseF or ΔssaV strains, recovered bacteria 12 h after infection and determined proteome compositions. Increased numbers of proteins characteristic for nutritional starvation were detected in STM ΔsseF and ΔssaV compared to WT. In addition, STM ΔssaV, but not ΔsseF showed signatures of increased exposure to stress by antimicrobial defenses, in particular reactive oxygen species, of the host cells. The proteomics analyses presented here support and extend the role of SIFs for the intracellular lifestyle of STM. We conclude that efficient manipulation of the host cell endosomal system by effector proteins of the SPI2-T3SS contributes to nutrition, as well as to resistance against antimicrobial host defense mechanisms.
Salmonella enterica is an invasive, facultative intracellular pathogen causing frequent infection of humans and animal hosts that range from gastroenteritis to typhoid fever, a systemic infection caused by human-restricted S. enterica serovars such as Typhi. S. enterica serovar Typhimurium (STM) is causative agent of gastroenteritis in humans and causes systemic infection in susceptible mouse lines.
This work provides the first systematic analysis of the impact of SPI2-T3SS-mediated endosomal remodeling of host cells on the global physiology of intracellular STM. For this, we performed quantitative proteomics of intracellular STM isolated from RAW264.7 macrophages and compared STM WT to highly attenuated STM ΔssaV defective in the SPI2-T3SS, and moderately attenuated ΔsseF, defective in a single SPI2-T3SS effector required to establish the full extent of remodeling of the host cell endosomal system. The analysis revealed distinct proteomic signatures for nutritional stress and compensatory regulation in both ΔsseF and ΔssaV strains that is discussed in detail below. In addition, the ΔssaV strain specifically revealed proteomic signatures of increased exposure to stress imposed by host cell antimicrobial defense mechanisms.