Identification of Type VI Secretion Systems Effector Proteins That Contribute to Interbacterial Competition in Salmonella Dublin.

Fernando A Amaya,Carlos J Blondel,Carlos A Santiviago,Andrea I Moreno-Switt,Dácil Rivera,David Pezoa,María F Barros-Infante

doi:10.3389/fmicb.2022.811932

Abstract

The Type VI Secretion System (T6SS) is a multiprotein device that has emerged as an important fitness and virulence factor for many Gram-negative bacteria through the injection of effector proteins into prokaryotic or eukaryotic cells via a contractile mechanism. While some effector proteins specifically target bacterial or eukaryotic cells, others can target both types of cells (trans-kingdom effectors). In Salmonella, five T6SS gene clusters have been identified within pathogenicity islands SPI-6, SPI-19, SPI-20, SPI-21, and SPI-22, which are differentially distributed among serotypes. Salmonella enterica serotype Dublin (S. Dublin) is a cattle-adapted pathogen that harbors both T6SSSPI-6 and T6SSSPI-19. Interestingly, while both systems have been linked to virulence and host colonization in S. Dublin, an antibacterial activity has not been detected for T6SSSPI-6 in this serotype. In addition, there is limited information regarding the repertoire of effector proteins encoded within T6SSSPI-6 and T6SSSPI-19 gene clusters in S. Dublin. In the present study, we demonstrate that T6SSSPI-6 and T6SSSPI-19 of S. Dublin CT_02021853 contribute to interbacterial competition. Bioinformatic and comparative genomic analyses allowed us to identify genes encoding three candidate antibacterial effectors located within SPI-6 and two candidate effectors located within SPI-19. Each antibacterial effector gene is located upstream of a gene encoding a hypothetic immunity protein, thus conforming an effector/immunity (E/I) module. Of note, the genes encoding these effectors and immunity proteins are widely distributed in Salmonella genomes, suggesting a relevant role in interbacterial competition and virulence. Finally, we demonstrate that E/I modules SED_RS01930/SED_RS01935 (encoded in SPI-6), SED_RS06235/SED_RS06230, and SED_RS06335/SED_RS06340 (both encoded in SPI-19) contribute to interbacterial competition in S. Dublin CT_02021853.

Highlights

Salmonellosis is a foodborne bacterial disease caused by different serotypes of Salmonella enterica (GBD-2017 et al, 2019)
Dublin CT_02021853, we performed a competition assay in MacConkey agar as it has been shown that bile salts upregulate the expression of T6SS-related genes in S
Our analysis identified two putative T6SS effector proteins encoded in SPI-19 (Figure 3; Table 4), that are conserved in S

Summary

Introduction

Salmonellosis is a foodborne bacterial disease caused by different serotypes of Salmonella enterica (GBD-2017 et al, 2019). Worldwide, this illness is linked to 95.1 million cases of gastroenteritis per year (GBD-2017 et al, 2019). The genus Salmonella includes more than 2,600 serotypes ( referred to as serovars) distributed between species S. enterica and S. bongori (Issenhuth-Jeanjean et al, 2014), which differ in clinical signs and host range (Uzzau et al, 2000). Dublin) represents a cattle-adapted pathogen that can lead to serious economic problems in bovine production, where it causes a severe systemic disease (Hoelzer et al, 2011; Nielsen et al, 2013). Dublin may constitute a serious risk for public health due to ingestion of contaminated milk by the human population (Small and Sharp, 1979; Fierer, 1983)

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