A trans-kingdom T6SS RNase effector targeting both prokaryotic and host cells for pathogenesis

The bacterial type VI secretion system (T6SS) mediates interactions with neighboring cells or the environment by secreting various effectors, yet T6SS RNase effectors have barely been studied. Here, we report a multifunctional trans-kingdom T6SS RNase effector, TseR, from Yersinia pseudotuberculosis (Yptb). TseR, an Ntox44 domain-containing effector secreted by T6SS-3, is a divalent cation-dependent RNase that preferentially cleaves single-stranded RNA, which can be inhibited by the cognate immunity protein TsiR. TseR mediated both contact-dependent and contact-independent T6SS killing of bacteria, with OmpC facilitating its entry into target cells during contact-independent killing. The global cleavage targets of TseR in Escherichia coli were identified via RNA-seq analysis. During infections, TseR facilitated pathogenicity by altering the gut microbiome and directly targeting eukaryotic host cells. This study provides valuable insights into the roles of the T6SS RNase effector and the Ntox44 family protein in bacterial competition and bacteria-host interactions.