TO BE OR NOT TO BE PLANKTONIC? REGULATION OF BIOFILM DEVELOPMENT IN THE CYANOBACTERIUM SYNECHOCOCCUS ELONGATUS

Information on the molecular mechanisms underlying biofilm formation in cyanobacteria is scarce, in spite of their environmental prevalence and the economic loss associated with these microbial assemblages. We recently demonstrated that the planktonic nature of the cyanobacterium Synechococcus elongatus is a result of a self-inhibition mechanism, which depends on the deposition of an inhibitory factor to the extracellular milieu (1, 2). 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 and leads to biofilm development. In addition to uncovering this inhibitory mechanism of biofilm formation, we identified genes that are essential for development of biofilms by S. elongatus. These genes encode small secreted proteins characterized by a “double glycine” secretion motif, as well as components of a transport system involved in secretion and maturation of proteins possessing this motif. Transcription of the genes that are essential for biofilm formation is repressed by the extracellular inhibitor and consequently, biofilm development is prevented.

A new isolate of S. elongatus from Waller Creek, one of the original locations of isolation of S. elongatus, exhibits robust biofilm formation in contrast to the laboratory strain, which as mentioned above, grows planktonically. We therefore propose that the planktonic nature of S. elongatus laboratory strains results from enhancement of the self-inhibitory mechanism and thus prevention of biofilm formation. Inactivation of the type II secretion/type IV system in the laboratory strain impairs the excretion of the inhibitor, thus resulting in biofilm development consequent to upregulation of genes essential for this process.

References

1. Schatz et al. (2013) Self-suppression of biofilm formation in the cyanobacterium Synechococcus elongatus. Environ Microbiol, 15(6), 1786-1794.

2. Nagar E, Schwarz R (2015) To be or not to be planktonic? Self-inhibition of biofilm development. Environ Microbiol. 17(5):1477-86.