Discovering how T6SS effectors are deployed in the recipient cytoplasm

Interbacterial competition is a key driver of the emergence of new bacterial strains.

A widely used strategy during interbacterial competition is delivering toxins into competitors’ cytoplasm, where they target conserved components.

The type VI secretion system (T6SS), a machine that delivers toxic effectors into neighboring cells, is a major player in interbacterial competitions. It fires an effector-loaded tube that penetrates the recipient cell envelope.

Although many T6SS effectors target the competitors’ cytoplasm, it is not known whether they are directly deployed there or rather deployed in the periplasm and then transported into the cytoplasm.

We have recently identified several domains within modular T6SS effectors that are fused specifically to cytoplasm-targeting toxic domains.

The new domains are required for competitor intoxication during competition but not for T6SS-mediated secretion of the effectors.

Therefore, we hypothesize that T6SS effectors are first deployed in the periplasm, where specialized domains such as these re-localize cytoplasm-targeting effectors into the recipient’s cytoplasm.

In IMCross, we will leverage our unique expertise in identifying and characterizing novel domains within effectors to go beyond the state-of-the-art and determine how cytoplasm-targeting T6SS effectors reach their target.

We will (1) reveal the initial site of T6SS effector deployment, (2) identify effector domains responsible for transport across the recipient inner membrane and determine whether they employ receptors in the process, and (3) establish a pipeline to discover re-localization domains and cytoplasm-targeting toxic domains in T6SS effectors.

The discovery of specialized T6SS effector re-localization domains will revolutionize our understanding of effector modularity and trafficking during competition.

Furthermore, such domains are key in developing tools to identify novel toxic domains and engineer synthetic toxins as alternative antibiotics.