A DNase T6SS effector requires its MIX domain for secretion

Abstract

Bacteria use diverse classes of secreted polymorphic toxins to outcompete bacterial rivals. The MIX domain defines a widespread class of polymorphic type VI secretion system (T6SS) effectors, many of which are horizontally shared. Although several MIX-effectors have been investigated, the role of the MIX domain and the activity of many fused toxin domains remain unknown. Here, we use the Vibrio parahaemolyticus MIX-effector VPA1263 to demonstrate that MIX is necessary for T6SS-mediated secretion; however, we find that it is dispensable for interaction with the secreted T6SS tail tube component, VgrG. We also identify a C-terminal HNH nuclease toxin domain in VPA1263, and we demonstrate that it functions as a DNase during interbacterial competition. Finally, we identify variants of the genomic island containing vpa1263 in various vibrios, each carrying a different cargo of antibacterial T6SS effectors or anti-phage defense systems. We propose that these genomic islands are hotspots for bacterial defensive weapons.

Recruitment of heterologous substrates by bacterial secretion systems for transkingdom translocation

“…MIX appears to be mainly located at the N-terminal region of the proteins, fused to C-terminal effector domains with antibacterial or anti-eukaryotic activity (Salomon et al, 2014). A recent work has shown that MIX sequence is necessary for the translocation of the effector from T6SS1 of Vibrio parahaemolyticus, demonstrating the importance of this signal in substrate recruitment (Fridman et al, 2022). Recently, it has been proposed that these sequences can be found not only in the effector protein, but also in a co-effector, which enables the loading and secretion of the toxin via the T6SS (Dar et al, 2022).…”