| Sumario: | Salmonella enterica is a species of bacterial pathogens that can produce different diseases from gastroenteritis to typhoid fever. Salmonella possesses two different virulence-related type III secretion systems (T3SSs) that are key elements in the interaction with the host cell. These systems mediate the translocation of effector proteins into the cytosol of the host cell where they interfere with different cellular processes to allow the pathogen entry and its survival inside vacuoles. We studied the S. enterica serovar Typhimurium SrfJ effector expression. We provide evidence for the existence of two distinct promoters that control the expression of srfJ. A proximal promoter, PsrfJ, responds to intravacuolar signals inside mammalian cells and is positively regulated by SsrB and PhoP and negatively regulated by RcsB. A second distal promoter, PiolE, is negatively regulated by the myo-inositol island repressor IolR, whereas it is expressed upon Salmonella colonization of plants. Importantly, we also found that inappropriate expression of srfJ leads to reduced proliferation inside macrophages whereas lack of srfJ expression increases survival and decreases activation of defense responses in plants. These observations suggest that SrfJ is a relevant factor in the interplay between Salmonella and host of different kingdoms. Transcriptomic carried out in human epithelial HeLa cells and murine RAW264.7 macrophages detected 16 genes that are significantly down-regulated and 12 genes that are significantly upregulated in response to the presence of SrfJ. Proteomic analysis revealed that SrfJ is involved in dephosphorylation of WNK1 and prevention of induction of HSP60. The last part of this thesis was focused on the development of a live Salmonella vaccine against Pseudomonas aeruginosa. As T3SS-mediated translocation can be used for efficient delivery of heterologous antigens to the cytosol of antigen-presenting cells, we tested the possibility of using Salmonella effectors SseJ, SrfJ, SlrP, SteA and SseK1, as carriers in the design of this vaccine. We finally developed a vaccine delivering the Pseudomonas antigen PcrV in fusion with SseJ through the T3SS. This vaccine protected mice against lethal infections with P. aeruginosa.
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