Cell Width Dictates Type VI Secretion Tail Length.

Area of Science:

• Microbiology
• Molecular Biology
• Cell Biology

Background:

• The type VI secretion system (T6SS) is a crucial apparatus for bacterial pathogenesis and inter-bacterial interactions.
• T6SSs are contractile injection systems (CISs) that utilize a spring-like mechanism to deliver effector proteins into target cells.
• T6SS structure includes a baseplate, Hcp needle, VgrG-PAAR spike, and a contractile sheath (TssB/TssC), anchored by a membrane complex.

Purpose of the Study:

• To investigate the regulatory mechanisms controlling the length of the T6SS tail.
• To determine if a tape measure protein (TMP) dictates T6SS tail length, as observed in other CISs.
• To elucidate the factors that limit TSS tail elongation.

Main Methods:

• Analysis of T6SS tail length in enteroaggregative Escherichia coli (E. coli).
• Overproduction of T6SS tail subunits to assess the role of component stoichiometry.
• Relocalization of the T6SS apparatus to the cell pole to study length regulation.
• Microscopy to observe T6SS tail elongation and termination.

Main Results:

• T6SS tail length was found to be constant in E. coli, indicating strict regulation.
• Component stoichiometry does not regulate T6SS tail length.
• TSS tail length is not controlled by a TMP, as longer tails were observed upon relocalization.
• TSS tail elongation ceases upon contact with the opposing cell membrane.

Conclusions:

• T6SS tail length is determined by the cell width, with elongation stopping at the opposite membrane.
• The absence of a TMP controlling length suggests a novel regulatory mechanism in T6SS.
• This finding provides insights into the assembly and functional constraints of bacterial secretion systems.