Anti-type VI tactics: bacterial defenses against type VI secretion system attacks

Survival of bacteria in dense and competitive microbial communities depends on their ability to access nutrients or outcompete neighboring cells. One of the key players in competition is the type VI secretion system (T6SS), a contractile nanomachine that injects a broad variety of effectors into competitors. However, target cells do not remain defenseless. Given the lethality of T6SS-mediated attacks, they have evolved countermeasures to detect, withstand, or resist such assaults: immunity proteins that neutralize effectors, activation of envelope stress pathways to mitigate damage, retaliatory responses to avoid recurrent attacks, physical barriers such as matrix polymers, or collective protection through aggregation. In this review article, we provide a comprehensive overview of these diverse strategies and emphasize the arms-race dynamics.