Cyanobacterial biofilms, which are highly
ubiquitous and inhabit diverse niches, are often associated with biological
fouling and cause severe economic loss. Information on the molecular mechanisms
underlying biofilm formation in cyanobacteria is scarce
We recently reported a mutant of the cyanobacterium S. elongatus, which developed biofilms under conditions that supported planktonic growth of the wild type strain. The biofilm-forming strain, T2SEΩ, is caused by inactivation a homolog of subunit E of type II secretion system. We demonstrated that the planktonic nature of the wild type strain is a result of a self-suppression mechanism, which depends on the deposition of a factor to the extracellular milieu.
Additionally, using a genetic approach we identified genes the products of which are required for biofilm development. Inactivation of these genes in all the biofilm-forming strains of S. elongatus including T2SEΩ abolished biofilm development, demonstrating that these genes are central to biofilm formation. These genes encode small proteins characterized by an N-terminus "double-glycine motif" as well as homologs of a transport/processing system. Such transporters are commonly involved in secretion and maturation of proteins possessing a GG-motif.
Transcripts levels of the biofilm-essential genes are substantially elevated in T2SEΩ compared to the wild type, and are decreased in this mutant when cultured in conditioned medium of wild type (which inhibits biofilm formation). The nature and possible mode of action of the putative secreted small proteins will be discussed.
