Live-cell imaging of Streptomyces conjugation

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Streptomyces are Gram-positive, mycelial soil bacteria.
• Conjugative plasmid transfer is vital for genetic exchange in bacteria.
• Understanding Streptomyces conjugation provides insights into microbial adaptation.

Purpose of the Study:

• To elucidate the mechanism of conjugative plasmid transfer in Streptomyces.
• To visualize and analyze the two-step conjugation process in living mycelium.
• To identify key proteins involved in intra-mycelial plasmid spreading.

Main Methods:

• Time-lapse fluorescence microscopy of differentially labeled donor and recipient Streptomyces strains.
• Genetic analysis of mutants deficient in plasmid spreading (spd mutant).
• Observation of hyphal contact and pore formation during conjugation.

Main Results:

• Plasmid transfer occurs at lateral wall contact points between donor and recipient hyphae.
• A pore formed by the FtsK-like DNA translocase TraB mediates initial plasmid transfer.
• Plasmids spread intracellularly within the recipient mycelium via invasion of adjacent compartments.
• Intra-mycelial spreading is dependent on a multi-protein apparatus at septal cross walls, including TraB and Spd proteins.

Conclusions:

• Streptomyces conjugation is a unique two-step process involving direct hyphal contact and subsequent intra-mycelial spreading.
• The FtsK-like TraB protein and Spd proteins are essential for efficient plasmid transfer and spreading.
• Intra-mycelial spreading is a critical adaptation for optimizing plasmid dissemination in the Streptomyces mycelial lifestyle.