A Novel Mechanism, Linked to Cell Density, Largely Controls Cell Division in Synechocystis

Abstract

ORCID IDs: 0000-0001-7618-4748 (M.I.); 0000-0001-8931-7722 (T.O.); 0000-0002-6113-9570 (R.S.).Many studies have investigated the various genetic and environmental factors regulating cyanobacterial growth. Here, we investigated the growth and metabolism of Synechocystis sp. PCC 6803 under different nitrogen sources, light intensities, and CO 2 concentrations. Cells grown on urea showed the highest growth rates. However, for all conditions tested, the daily growth rates in batch cultures decreased steadily over time, and stationary phase was obtained with similar cell densities. Unexpectedly, metabolic and physiological analyses showed that growth rates during log phase were not controlled primarily by the availability of photoassimilates. Further physiological investigations indicated that nutrient limitation, quorum sensing, light quality, and light intensity (self-shading) were not the main factors responsible for the decrease in the growth rate and the onset of the stationary phase. Moreover, cell division rates in fed-batch cultures were positively correlated with the dilution rates. Hence, not only light, CO 2 , and nutrients can affect growth but also a cell-cell interaction. Accordingly, we propose that cell-cell interaction may be a factor responsible for the gradual decrease of growth rates in batch cultures during log phase, culminating with the onset of stationary phase.

Analysis of the light intensity dependence of the growth ofSynechocystisand of the light distribution in a photobioreactor energized by 635 nm light

“…The intensive exploitation of this microorganism for industrial uses strongly depends on the choice of optimal growth conditions, main operational parameters including culture density ( Esteves-Ferreira et al, 2017 ; Straka & Rittmann, 2018 ), pH ( Touloupakis et al, 2016 ), temperature ( Panda et al, 2006 ), mixing rate and light environment ( Touloupakis et al, 2016 ; Singh et al, 2009 ). Even though extensive investigation showed that Synechocystis productivity is sensitive to most of the aforementioned operational parameters ( Yu et al, 2013 ; Burrows et al, 2009 ; Nanjo et al, 2010 ; Chaves, Kirst & Melis, 2015 ), it is undoubted that productivity is tightly coupled with the light absorption efficiency of optical energy conversion systems.…”

Increasing the Photoautotrophic Growth Rate of Synechocystis sp. PCC 6803 by Identifying the Limitations of Its Cultivation

“…Alternatively, the amount of sulfate can be increased to lift the sulfur limitation of high density cultures (Figure S5, Supporting Information), which will then be limited by nitrogen instead (Table S3, Supporting Information). In a recent paper, it was proposed that Synechocystis enters stationary phase due to cell–cell interactions rather than self‐shading or other nutrient limitation. However, the final density those authors observed when cells entered stationary phase was 0.12 gDW L −1 on average, which is far below what we observe (2.88 gDW L −1 ), indicating that growth in their experiment is halted for other, unknown, reasons.…”

Structural Determinants and Their Role in Cyanobacterial Morphogenesis

“…E. coli ftsZ is transcribed in an operon together with ftsA (absent in cyanobacteria) and ftsQ (i.e., the ftsQAZ operon), whereas no ftsQZ operon was observed in Anabaena , Synechocystis nor Synechococcus , where ftsZ is independently transcribed from ftsQ instead [ 109 , 147 ], contrasting the identified ftsQZ operon structure in M. aeruginosa [ 148 ]. Given that cyanobacteria are photosynthetic organisms, it is not surprising that cell division and consequently ftsZ expression patterns are dependent on the circadian clock with an expression peak near dusk in Synechococcus and Synechocystis [ 147 , 149 ]. This circadian rhythmicity in Synechococcus is governed by the essential circadian clock protein kinase KaiC, through inhibition of Z-ring formation without impacting the cellular FtsZ protein levels [ 150 ].…”