Unlocking the Constraints of Cyanobacterial Productivity: Acclimations Enabling Ultrafast Growth

Abstract

Harnessing the metabolic potential of photosynthetic microbes for next-generation biotechnology objectives requires detailed scientific understanding of the physiological constraints and regulatory controls affecting carbon partitioning between biomass, metabolite storage pools, and bioproduct synthesis. We dissected the cellular mechanisms underlying the remarkable physiological robustness of the euryhaline unicellular cyanobacterium Synechococcus sp. strain PCC 7002 (Synechococcus 7002) and identify key mechanisms that allow cyanobacteria to achieve unprecedented photoautotrophic productivities (~2.5-h doubling time). Ultrafast growth of Synechococcus 7002 was supported by high rates of photosynthetic electron transfer and linked to significantly elevated transcription of precursor biosynthesis and protein translation machinery. Notably, no growth or photosynthesis inhibition signatures were observed under any of the tested experimental conditions. Finally, the ultrafast growth in Synechococcus 7002 was also linked to a 300% expansion of average cell volume. We hypothesize that this cellular adaptation is required at high irradiances to support higher cell division rates and reduce deleterious effects, corresponding to high light, through increased carbon and reductant sequestration.

Deciphering cyanobacterial phenotypes for fast photoautotrophic growth via isotopically nonstationary metabolic flux analysis

“…Such observations, together with cultivation experiments using organic acids, indicated that the TCA cycle and its associated anabolic pathways in Synechococcus 2973 operate at lower rates than in E. coli , which would limit production of chemicals from the cyanobacterial TCA cycle [ 4 ]. In Synechococcus 2973, the photosynthetic capacity generates sugar phosphates readily (FBP phosphatase/aldolase, fructose-bisphosphatase, transketolase, and RuBisCO reactions) that can enhance its growth [ 31 – 33 ] and could potentially be applied for biotechnological productions [ 34 ].…”

Construction of a Shuttle Vector Using an Endogenous Plasmid From the Cyanobacterium Synechocystis sp. PCC6803

“…Maintenance of the plasmid in the absence of antibiotic selection was assayed based on the shuttle vector maintenance protocol in Syn7942 with some minor modifications ( Chen et al, 2016b ). The test was conducted at a similar stage (1-week-old cultures) because Syn6803 and Syn7942 have similar doubling times (between 7 and 12 h) ( Bernstein et al, 2016 ). Cells with pSCB-YFP were grown in medium supplemented with Sp 10 μg/ml for 7 days, then inoculated into two flasks, each containing 50 ml of medium, one containing 10 μg/ml Sp, the other without antibiotic.…”

Life cycle of a cyanobacterial carboxysome

“…We used time-lapse fluorescence microscopy to track fluorescently labeled carboxysomes in single Synechococcus sp. PCC 7002 (hereafter PCC 7002) cells, chosen for their fast growth rate (13) and industrial relevance (14)(15)(16). Unlike bulk culture techniques, microscopy enables analysis of individual carboxysomes and has been used to describe carboxysome organization within the cell (17,18).…”