Cell surface composition and ionic strength mediate fast sedimentation in the cyanobacteriumSynechococcus 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 describeSynechococcus elongatusPCC 7942-KU, a novel domesticated substrain of the model cyanobacteriumSynechococcus elongatusPCC 7942, which presents a fast-sedimenting phenotype. Under higher ionic strengths the sedimentation rate increases leading to complete sedimentation in just 12 h. Through whole genome sequencing and gene deletion, we demonstrate that the Group 3 alternative sigma factor F (SigF) plays a key role in cell sedimentation. In addition, sedimentation analysis of an unpiliated mutant and differences in surface hydrophobicity suggest that mutations in SigF lead to significant changes of cell surface structures and, consequentially, 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.

Cyanobacteria newly isolated from marine volcanic seeps display rapid sinking and robust, high density growth

“…Given UTEX 3222’s lack of phototactic motility, two differing phenomena could drive this settling behavior-aggregation of single cells into larger particles that sink more readily and/or individual cells having faster settling rates. Aggregation plays a key role in the behavior of fast-settling mutants of PCC 7942 cyanobacteria 51 , but can be predicated on the ionic strength of the settling medium and can be mimicked with chemical flocculants 49 . We were curious whether individual cells had advantageous settling behavior, because this could drive the sinking of biomass in more dilute conditions, such as cells growing in marine habitats and affecting natural carbon cycles 52 .…”

EXCRETE enables deep proteomics of the microbial extracellular environment

“…The T1SS, for example, plays a role in heterocyst development and deposition of the S-layer [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] .…”