Cell surface composition, released polysaccharides, and ionic strength mediate fast sedimentation in the cyanobacterium Synechococcus elongatusPCC 7942

Abstract

Cyanobacteria are photosynthetic prokaryotes of high ecological and biotechnological relevance that have been cultivated in laboratories around the world for more than 70 years. Prolonged laboratory culturing has led to multiple microevolutionary events and the appearance of a large number of ‘domesticated’ substrains among model cyanobacteria. Despite its widespread occurrence, strain domestication is still largely ignored. In this work we describe Synechococcus elongatus PCC 7942‐KU, a novel domesticated substrain of the model cyanobacterium S. elongatus PCC 7942, which presents a fast‐sedimenting phenotype. Under higher ionic strengths the sedimentation rate increased leading to complete sedimentation in just 12 h. Through whole genome sequencing and gene deletion, we demonstrated that the Group 3 alternative sigma factor F plays a key role in cell sedimentation. Further analysis showed that significant changes in cell surface structures and a three‐fold increase in released polysaccharides lead to the appearance of a fast‐sedimenting phenotype. This work sheds light on the determinants of the planktonic to benthic transitions and provides genetic targets to generate fast‐sedimenting strains that could unlock cost‐effective cyanobacterial harvesting at scale.

Structure of the SigF1-dependent <i>pilA1</i> gene promoter and characterization of the light-activated response in the cyanobacterium <i>Synechococcus elongatus</i> PCC 7942

“…Correlating with the SigF1-dependence of pilA1 gene expression, SigF1-deficient strains were found to easily precipitate at the bottom in liquid culture without agitation (Fig. S5), as is consistent with a recent independent observation (Zedler et al, 2023).…”

“…In this study, we found that the pilA1 gene, encoding type IV pilin, is transcribed by RNA polymerase containing the group 3 sigma factor SigF1 in Synechococcus, which appears to be responsible for the sedimentation phenotype (Zedler et al, 2023).…”

EXCRETE enables deep proteomics of the microbial extracellular environment

“…The T1SS, for example, plays a role in heterocyst development and deposition of the Slayer [13][14][15][16] . And T4P are involved in phototaxis, DNA uptake, aggregation, and flotation [17][18][19][20][21][22] . Interestingly, the recent discovery of multiple protein secretion mechanisms that do not involve the aforementioned systems suggests that there may be a myriad of secreted proteins which remain largely unexplored [23][24][25][26] .…”