Role of the Glycosyltransferase, OgtB, in Biofilm Self-Suppression in the Cyanobacterium Synechococcus elongatus PCC7942

Post-translational modifications, including phosphorylation, acetylation and glycosylation, are common mechanisms regulating protein function and quality control. O-linked β-N-acetylglucosamine transferase (Ogt) is the enzyme responsible for covalent attachment of a single β-N-acetylglucosamine to the hydroxyl group of serine or threonine residues. This glycosylation may compete with phosphorylation of the same sites with one modification preventing the other.

We identified a biofilm self-suppression mechanism in the cyanobacterium Synechococcus elongatus PCC7942. Inactivation of a gene encoding a homolog of the ATPase subunit of type II protein secretion or type IV pilus assembly systems impairs the inhibitory process resulting in a biofilm-forming mutant, T2SEΩ. We recently revealed that inactivation of ogt in S. elongatus also impairs the biofilm self-inhibitory mechanism. The mutant strain, OgtBΩ, develops biofilms and is characterized by impaired protein secretion and aberrant pilus assembly. Additionally, the mutant does not glycosylate the pilin subunit PilA. Furthermore, modification of the conserved lysine residue essential for catalytic activity to alanine (K445A) abolished biofilm development and prevented PilA glycosylation. Altogether, this study demonstrates requirement of PilA glycosylation for adequate pilus formation and biofilm self-suppression in S. elongatus.