%0 Journal Article %A Sibinelli de Sousa, Stephanie %A Takuno Hespanhol, Julia %A Matsuyama, Bruno %A Mesnage, Stephane %A Nicastro, Gianlucca %A Sanchez Limache, Daniel Enrique %A Francisco de Souza, Robson %A Bayer Santos, Ethel %T A family of T6SS antibacterial effectors related to L,D-transpeptidases targets the Peptidoglycan %D 2020 %J Access Microbiology, %V 2 %N 7A %@ 2516-8290 %C 63 %R https://doi.org/10.1099/acmi.ac2020.po0033 %I Microbiology Society, %X Type VI secretion systems (T6SSs) are contractile nanomachines widely used by bacteria to intoxicate competitors. Salmonella Typhimurium encodes a T6SS within the Salmonella pathogenicity island 6 (SPI-6) that is used during competition against species of the gut microbiota. We characterized a new SPI-6 T6SS antibacterial effector named Tlde1 (type VI L,D-transpeptidase effector 1). Tlde1 is toxic in target-cell periplasm and its toxicity is neutralized by co-expression with immunity protein Tldi1 (type VI L,D-transpeptidase immunity 1). Time-lapse microscopy revealed that intoxicated cells display altered cell division and lose cell envelope integrity. Bioinformatics analysis showed that Tlde1 is evolutionarily related to L,D-transpeptidases. Point mutations on conserved histidine121 and cysteine131 residues eliminated toxicity. Co-incubation of purified recombinant Tlde1 and peptidoglycan tetrapeptides showed that Tlde1 displays both L,D-carboxypeptidase activity by cleaving GM-tetrapeptides between meso-diaminopimelic acid3 and D-alanine4, and L,D-transpeptidase exchange activity by replacing D-alanine4 for a non-canonical D-amino acid. Tlde1 constitutes a new family of T6SS effectors widespread in Proteobacteria. This work increases our knowledge about the bacterial effectors used in interbacterial competitions and provides molecular insight into a new mechanism of bacterial antagonism. %U https://www.microbiologyresearch.org/content/journal/acmi/10.1099/acmi.ac2020.po0033