SELF-SUPPRESSION OF BIOFILM DEVELOPMENT IN THE CYANOBACTERIUM SYNECHOCOCCUS ELONGATUS: ROLE OF EXTRACELLULAR INHIBITOR(S) AND THE HFQ RNA CHAPERONE HOMOLOG

Cyanobacterial biofilms, which are highly ubiquitous and inhabit diverse niches, are often associated with biological fouling and cause severe economic loss. In contrast to the wealth of knowledge on biofilms in heterotrophic bacteria, information on the molecular mechanisms underlying biofilm formation in cyanobacteria is scarce. We recently reported a self-suppression mechanism, which prevents biofilm development by the cyanobacterium Synechococcus elongatus. Inactivation of Synpcc7942_ 2071 impairs the self-suppression process and results in biofilm development (1, 2). This gene encodes subunit E of type II secretion system (T2SE) or PilB of the type IV pilus biogenesis system (subunits of these systems share high homology). We recently demonstrated that inactivation of the S. elongatus RNA-chaperone homolog, Hfq, also impairs the biofilm self-inhibitory process; inactivation of the hfq-gene results in biofilm development. Similarly to the mutant in T2SE/PilB, the Hfq-mutant does not form cell-pili and is impaired in protein secretion. Interestingly, studies of cell motility in the cyanobacterium Synechocystis sp. PCC6803 revealed that the Hfq of this cyanobacterium interacts with T2SE/PilB. Therefore, we suggest that Hfq serves for inhibition of biofilm formation via modulation of the type II protein secretion/type IV pilus assembly apparatus. Additionally, the Synpcc7942_0862 gene, which encodes a hypothetical protein highly conserved among cyanobacteria, is also essential for biofilm-inhibition. Inactivation of this gene impairs protein secretion, eliminates cell pili and results in biofilm development. The possible involvement of Hfq and the product of the Synpcc7942_0862 gene in modulation of type II protein secretion/type IV pilus assembly systems will be discussed.

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.