Contact-dependent growth inhibition toxins exploit multiple independent cell-entry pathways

Area of Science:

• Microbiology
• Bacterial Genetics
• Molecular Biology

Background:

• Contact-dependent growth inhibition (CDI) is a bacterial cell-to-cell communication system.
• CDI+ bacteria deliver toxins via filamentous CdiA effector proteins to inhibit neighboring cells.
• CdiA C-terminal (CdiA-CT) toxins exhibit high variability and diverse activities.

Purpose of the Study:

• To elucidate the functional domains of CdiA-CT and their roles in toxin delivery.
• To identify bacterial factors involved in CdiA-CT translocation into target cells.
• To explore the potential for repurposing CDI mechanisms for antimicrobial delivery.

Main Methods:

• Genetic analysis to identify mutations conferring resistance to CdiA-CT toxins.
• Characterization of CdiA-CT domain functions (nuclease activity and transport).
• Fusion of CdiA nuclease domains with heterologous N-terminal translocation domains.

Main Results:

• CdiA-CT comprises two domains: a C-terminal nuclease and an N-terminal transport domain.
• Mutations in inner-membrane proteins (e.g., ptsG, metI) confer resistance to specific CdiA-CTs.
• Resistance is mediated by the N-terminal domain's interaction with specific inner-membrane receptors for translocation.

Conclusions:

• The N-terminal domain of CdiA-CT acts as a specific receptor-binding module for toxin import.
• CDI toxin delivery involves translocation into the cytoplasm via inner-membrane proteins.
• CDI translocation mechanisms offer a platform for delivering novel antimicrobial agents into Gram-negative bacteria.