Transcriptomic and Phenomic Investigations Reveal Elements in Biofilm Repression and Formation in the Cyanobacterium Synechococcus elongatus PCC 7942

Abstract

Biofilm formation by photosynthetic organisms is a complex behavior that serves multiple functions in the environment. Biofilm formation in the unicellular cyanobacterium Synechococcus elongatus PCC 7942 is regulated in part by a set of small secreted proteins that promotes biofilm formation and a self-suppression mechanism that prevents their expression. Little is known about the regulatory and structural components of the biofilms in PCC 7942, or response to the suppressor signal(s). We performed transcriptomics (RNA-Seq) and phenomics (RB-TnSeq) screens that identified four genes involved in biofilm formation and regulation, more than 25 additional candidates that may impact biofilm formation, and revealed the transcriptomic adaptation to the biofilm state. In so doing, we compared the effectiveness of these two approaches for gene discovery.

Cyanobacterial sigma factor controls biofilm-promoting genes through intra- and intercellular pathways

“…A recent study showed that the inactivation of the gene Synpcc7942_1510, which encodes a homolog of the Sigma F factor known as SigF1, results in biofilm development [21]. Briefly, a pooled barcoded transposon library, RB-TnSeq, was grown, biofilms were formed, and sequencing of the barcodes indicated the abundance of each mutant in both the biofilm and the planktonic fractions.…”

“…This action subsequently leads to the repression of genes that promote biofilm formation, which in turn represses biofilm-promoting genes (Fig. 8, top panel, thick T-bar; [21][22][23][24][25]). Therefore, sigF1-inactivation, which abrogates pili formation, alleviates a major repression pathway, most likely due to disruption of the inhibitor(s) secretion process.…”

“…Recent genetic screening implied involvement of a SigF-homolog of the freshwater unicellular cyanobacterium Synechococcus elongatus PCC 7942 in regulation of biofilm formation [21]. Previous studies from our group have identified a biofilm-suppression mechanism in this cyanobacterium, which relies on extracellular inhibitor(s) that repress transcription of the ebfG -operon.…”

“…Cumulative evidence indicates that impairment of the type IV pilus assembly complex (T4P) disrupts the suppression mechanism leading to biofilm development (Fig. 1; also see [21, 22, 27, 28]), and affects the exoproteome, consistent with a shared complex serving in type IV pilus formation and type II secretion (cite Yegorov) Intriguingly, the RNA chaperone Hfq and a conserved cyanobacterial protein called EbsA ( e ssential for b iofilm s uppression protein A) are part of the cyanobacterial T4P complex [28, 29]. The glycosyl transferase Ogt, responsible for modifying the pilus subunit PilA, is required for pilus formation and biofilm-suppression [30].…”

An unexpected role for leucyl aminopeptidase in UV tolerance revealed by a genome-wide fitness assessment in a model cyanobacterium

“…Random barcode transposon site sequencing (RB-TnSeq) is a methodology that has proven to be particularly useful for elucidating genes that are most important to sustain a variety of conditions and processes in the model cyanobacterium Synechococcus elongatus PCC 7942 ( 9 – 12 ). In this study we leveraged RB-TnSeq to elucidate the gene set that is most critical in S. elongatus for tolerating UVR stress under a light cycle that resembles natural UVR dosage and short-wavelength spectral quality.…”