Synechococcus elongatus PCC7942: a cyanobacterium cell factory for producing useful chemicals and fuels under abiotic st
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ORIGINAL ARTICLE
Synechococcus elongatus PCC7942: a cyanobacterium cell factory for producing useful chemicals and fuels under abiotic stress conditions Dimitrios Vayenos1 · George Em. Romanos2 · George C. Papageorgiou1 · Kostas Stamatakis1 Received: 20 August 2019 / Accepted: 1 April 2020 © Springer Nature B.V. 2020
Abstract Sucrose, a compatible osmolyte in cyanobacteria, functions both as an energy reserve and as osmoprotectant. Sugars are the most common substrates used by microorganisms to produce hydrogen ( H2) by means of anaerobic dark fermentation. Cells of the unicellular, non-nitrogen fixing, freshwater cyanobacterium Synechococcus elongatus PCC7942 accumulate sucrose under salt stress. In the present work, we used this cyanobacterium and a genetically engineered strain of it (known as PAMCOD) to investigate the optimal conditions for (a) photosynthetic activity, (b) cell proliferation and (c) sucrose accumulation, which are necessary for H 2 production via anaerobic dark fermentation of the accumulated sucrose. PAMCOD (Deshnium et al. in Plant Mol Biol 29:897–902, 1995) contains the gene codA that codes for choline oxidase, the enzyme which converts choline to the zwitterion glycine betaine. Glycine betaine is a compatible osmolyte which increases the salt tolerance of Synechococcus elongatus PCC7942. Furthermore, glycine betaine maintains cell proliferation under salt stress and results in increased sucrose accumulation. In the present study, we examine the environmental factors, such as the NaCl concentration, the culture medium pH, and the carbon dioxide content of the air bubbled through it. At optimal conditions, sucrose accumulated in the cyanobacteria cells up to 13.5 mol per mole Chl a. Overall, genetically engineered Synechococcus elongatus PCC7942 produces sucrose in sufficient quantities such that it may be a viable alternative (a) to sucrose synthesis, and (b) to H2 formation via anaerobic dark fermentation. Keywords Cyanobacteria · Salt stress · Sucrose · Dark fermentation · Hydrogen
Introduction Cyanobacteria are photoautotrophic prokaryotes which absorb sunlight and convert C O2 and H 2O to organic compounds via photosynthesis. They are important primary producers and it is estimated that 20–30% of organic carbon on the Earth is derived from photosynthetic CO2 fixation by Dedicated to Prof. Norio Murata, a leading scientist in photosynthesis research * Kostas Stamatakis [email protected] 1
Institute of Biosciences and Applications, National Center for Scientific Research Demokritos, Aghia Paraskevi, 15310 Attikis, Greece
Institute of Nanoscience and Nanotechnology, National Center for Scientific Research Demokritos, Aghia Paraskevi, 15310 Attikis, Greece
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cyanobacteria (Waterbury et al. 1979). Even though plants, algae and cyanobacteria are all capable of oxygenic photosynthesis, the efficiency of cyanobacteria is tenfold higher than that of plants and algae (Li et al. 2008). Cyanobacteria are intensively investigated as photosynthetic producers of organic co
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