Abstract
<jats:p>Vibrio cholerae employs the Type VI Secretion System (T6SS) to outcompete neighboring bacteria and establish successful colonization within the polymicrobial gut. The T6SS effector VgrG1 contains a C-terminal Actin Crosslinking Domain (VgrG1-ACD), well known for irreversibly crosslinking eukaryotic actin to disrupt the host cytoskeleton. However, whether VgrG1-ACD also contributes directly to interbacterial competition has remained unexplored. Here, we identify a previously unrecognized bacterial target of VgrG1-ACD: MreB, the bacterial actin homolog essential for cell shape, cell wall synthesis, and cytoskeletal organization. We demonstrate that VgrG1-ACD specifically binds Escherichia coli MreB, resulting in pronounced morphological defects and impaired bacterial growth. Notably, unlike its activity toward mammalian actin, VgrG1-ACD targets MreB without crosslinking it, revealing a distinct mode of action. These findings expand the functional repertoire of VgrG1-ACD beyond host-directed virulence and uncover a dual-targeting strategy through which a single T6SS effector manipulates both mammalian actin and its bacterial homolog, likely enhancing V. cholerae fitness during interbacterial competition and host colonization.</jats:p>