The M91 metallopeptidase domain of the T6SS effector protein SED_RS06335 encoded in Salmonella Dublin SPI-19 exhibits antibacterial activity

Objective The Type VI Secretion System (T6SS) is a contractile apparatus made of several proteins playing a significant role in the fitness and virulence of many Gram-negative bacteria. The SPI-19 T6SS gene cluster is a virulence factor of Salmonella Dublin contributing to host colonization and antibacterial activity. Previously, we demonstrated that SED_RS06335 (an Rhs protein with a C-terminal M91 domain) is responsible for antibacterial activity of the T6SS SPI−19 ; however, the role of the M91 domain in this phenotype is unknown. Thus, the objective of this study is to provide experimental evidence that the antibacterial activity of SED_RS06335 effector is attributable to its C-terminal M91 domain. Results Here, we determine through interbacterial competition and heterologous expression assays that M91 domain of SED_RS06335 displays antibacterial activity. Furthermore, a three-dimensional structural model of M91 domain revealed a high similarity with the metallopeptidase neurotoxin type A (BotA) from Clostridium botulinum . Interestingly, our results suggest that the M91 domain is responsible for the antibacterial activity of the SED_RS06335 effector in Salmonella Dublin.