A cyanobacterial sigma factor F controls biofilm-promoting genes through intra- and intercellular pathways

Area of Science:

• Microbiology
• Molecular Biology
• Biotechnology

Background:

• Cyanobacteria form phototrophic biofilms with industrial relevance.
• A biofilm-suppression mechanism involving an extracellular inhibitor was previously observed in *Synechococcus elongatus* PCC 7942.
• This mechanism suggested a role for intercellular communication in cyanobacteria.

Purpose of the Study:

• To investigate the role of RNA polymerase sigma factors SigF1 and SigF2 in the biofilm-suppression mechanism of *Synechococcus elongatus* PCC 7942.
• To elucidate the regulatory pathways governing cyanobacterial biofilm formation and intercellular communication.

Main Methods:

• Genetic inactivation of *sigF1* and *sigF2* in *Synechococcus elongatus* PCC 7942.
• Transcriptome analyses to identify gene regulons controlled by SigF1 and SigF2.
• Analysis of pilus assembly and extracellular inhibitor presence in conditioned medium.

Main Results:

• SigF1, but not SigF2, is essential for the biofilm-suppression mechanism.
• Loss of SigF1 leads to reduced transcription of pilus subunit genes, preventing pilus assembly and inhibitor secretion.
• SigF1 inactivation upregulates matrix component and secretion system genes, indicating derepression of biofilm-promoting factors.

Conclusions:

• SigF1 is a critical regulator of cyanobacterial intercellular communication, controlling biofilm formation.
• The pilus assembly complex is involved in the secretion of the biofilm inhibitor.
• SigF1 exerts both extracellular (via inhibitor) and intracellular regulation on biofilm development.