Identification and characterization of novel effectors secreted by the type VI secretion system in Salmonella spp

Author(s)

Stephanie Sibinelli de Sousa

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Ciências Biomédicas (ICB/SDI)
• Defense date: 2023-12-04

Examining board members

Ethel Bayer Santos; Rodrigo da Silva Galhardo; Cristiano Gallina Moreira; Uelinton Manoel Pinto

• Advisor: Ethel Bayer Santos; Robson Francisco de Souza

Abstract

Bacteria live in complex polymicrobial communities and employ diverse strategies to compete for resources. Gram-negative bacteria encode a type VI protein secretion system (T6SS) capable of delivering effectors into both eukaryotic and prokaryotic target cells. Salmonella spp. encode five phylogenetically distinct T6SSs in different pathogenicity islands (Salmonella Pathogenicity Island): SPI-6, SPI-19, SPI-20, SPI-21, and SPI-22. Previous studies highlighted the importance of SPI-6 T6SS of S. Typhimurium and SPI-19 T6SS of S. Gallinarum in bacterial competition and vertebrate host infections, respectively. However, few effectors secreted by Salmonella T6SSs have been described. In this context, the project aimed to identify and characterize new effectors of Salmonella T6SS using computational and experimental approaches. Initially, we identified and characterized a new family of antibacterial effectors that target the cell wall of competing bacteria via a novel mechanism of action: L, D-carboxipeptidase and L,D-transpeptidase D-amino acid exchange activity. Subsequently, employing a more comprehensive approach, co-immunoprecipitation assays with the structural components of T6SS (hemolysin coregulated proteins, Hcps) were conducted, and their interaction partners were identified via mass spectrometry. In addition, 10,000 Salmonella genomes were examined to identify new T6SS effectors using in silico strategies. As a result, several possible effectors were identified, revealing a wide diversity, which contained previously unknown protein domains. A potential effector (STox15) was chosen for biochemical and functional characterization to validate our analyses. The results showed that STox15 and SImm15 constitute a new T6SS antibacterial effector and immunity protein pair. Overall, this project expanded our knowledge of Salmonella T6SS effectors and their significance in bacterial competition and vertebrate host infections. (AU)

• FAPESP's process: 21/09162-0 - Study of the function of different Hcp proteins encoded by Salmonella spp
• Grantee: Stephanie Sibinelli de Sousa
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)