Cyanobacterial flocculation as a defence against bacterial predation.

Area of Science:

• Microbiology
• Cyanobacterial Biology
• Bacterial Pathogenesis

Background:

• Cyanobacteria, like Synechocystis sp. PCC 6803, can form flocs (large cell aggregates) through regulated processes involving type IV pili and extracellular polysaccharides.
• The ecological benefits of cyanobacterial flocculation are not well understood, as it can sometimes impede growth under laboratory conditions.

Purpose of the Study:

• To investigate if cyanobacterial flocculation serves as a defense mechanism against bacterial predation.
• To determine the role of Pseudomonas aeruginosa's type VI secretion system (T6SS) in preying on cyanobacteria.

Main Methods:

• Co-culturing wild-type Synechocystis with Pseudomonas aeruginosa and comparing it to a non-flocculating Synechocystis mutant.
• Monitoring the growth of both P. aeruginosa and Synechocystis populations.
• Assessing Synechocystis cell lysis and P. aeruginosa's access to photosynthetic products.

Main Results:

• Exposure to live P. aeruginosa cells strongly induced flocculation in Synechocystis.
• Synechocystis flocculation significantly reduced P. aeruginosa growth and Synechocystis cell lysis.
• Flocculation limited P. aeruginosa's access to photosynthetic products, mitigating its impact on Synechocystis.

Conclusions:

• Cyanobacterial flocculation is a defense strategy against microbial predation, particularly by bacteria utilizing type VI secretion systems.
• Pseudomonas aeruginosa employs its type VI secretion system for direct predation on cyanobacteria.
• Flocculation enhances cyanobacterial survival by limiting pathogen proliferation and damage.