Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory Title Metabolic phenotyping of the cyanobacterium Synechocystis 6803 engineered for production of alkanes and free fatty acids Permalink (original) (raw)
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Biotechnology for biofuels, 2016
Among the three model cyanobacterial species that have been used for engineering a system for photosynthetic production of free fatty acids (FFAs), Synechococcus elongatus PCC7942 has been the least successful; the FFA-excreting mutants constructed from this strain could attain lower rates of FFA excretion and lower final FFA concentrations than the mutants constructed from Synechocystis sp. PCC6803 and Synechococcus sp. PCC7002. It has been suggested that S. elongatus PCC7942 cells suffer from toxicity of FFA, but the cause of the low productivity has remained to be determined. By modulating the expression level of the acyl-acyl carrier protein thioesterase and raising the light intensity during cultivation, FFA secretion rates comparable to those obtained with the other cyanobacterial species were attained with an engineered Synechococcus elongatus mutant (dAS1T). The final FFA concentration in the external medium was also higher than previously reported for other S. elongatus mut...
Cyanobacteria are an important group of photoautotrophic organisms that can synthesize valuable bio-products by harnessing solar energy. They are endowed with high photosynthetic efficiencies and diverse metabolic capabilities that confer the ability to convert solar energy into a variety of biofuels and their precursors. However, less well studied are the similarities and differences in metabolism of different species of cyanobacteria as they pertain to their suitability as microbial production chassis. Here we assemble, update and compare genome-scale models (iCyt773 and iSyn731) for two phylogenetically related cyanobacterial species, namely Cyanothece sp. ATCC 51142 and Synechocystis sp. PCC 6803. All reactions are elementally and charge balanced and localized into four different intracellular compartments (i.e., periplasm, cytosol, carboxysome and thylakoid lumen) and biomass descriptions are derived based on experimental measurements. Newly added reactions absent in earlier models (266 and 322, respectively) span most metabolic pathways with an emphasis on lipid biosynthesis. All thermodynamically infeasible loops are identified and eliminated from both models. Comparisons of model predictions against gene essentiality data reveal a specificity of 0.94 (94/100) and a sensitivity of 1 (19/19) for the Synechocystis iSyn731 model. The diurnal rhythm of Cyanothece 51142 metabolism is modeled by constructing separate (light/dark) biomass equations and introducing regulatory restrictions over light and dark phases. Specific metabolic pathway differences between the two cyanobacteria alluding to different bio-production potentials are reflected in both models. Citation: Saha R, Verseput AT, Berla BM, Mueller TJ, Pakrasi HB, et al. (2012) Reconstruction and Comparison of the Metabolic Potential of Cyanobacteria Cyanothece sp. ATCC 51142 and Synechocystis sp. PCC 6803. PLoS ONE 7(10): e48285.
PLoS Computational Biology, 2013
Cyanobacteria are versatile unicellular phototrophic microorganisms that are highly abundant in many environments. Owing to their capability to utilize solar energy and atmospheric carbon dioxide for growth, cyanobacteria are increasingly recognized as a prolific resource for the synthesis of valuable chemicals and various biofuels. To fully harness the metabolic capabilities of cyanobacteria necessitates an in-depth understanding of the metabolic interconversions taking place during phototrophic growth, as provided by genome-scale reconstructions of microbial organisms. Here we present an extended reconstruction and analysis of the metabolic network of the unicellular cyanobacterium Synechocystis sp. PCC 6803. Building upon several recent reconstructions of cyanobacterial metabolism, unclear reaction steps are experimentally validated and the functional consequences of unknown or dissenting pathway topologies are discussed. The updated model integrates novel results with respect to the cyanobacterial TCA cycle, an alleged glyoxylate shunt, and the role of photorespiration in cellular growth. Going beyond conventional flux-balance analysis, we extend the computational analysis to diurnal light/ dark cycles of cyanobacterial metabolism.
Photosynthesis Research, 2020
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 (H 2) 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 H 2 formation via anaerobic dark fermentation.
Biotechnology for Biofuels, 2019
Background: Cyanobacteria are potential sources for third generation biofuels. Their capacity for biofuel production has been widely improved using metabolically engineered strains. In this study, we employed metabolic engineering design with target genes involved in selected processes including the fatty acid synthesis (a cassette of accD, accA, accC and accB encoding acetyl-CoA carboxylase, ACC), phospholipid hydrolysis (lipA encoding lipase A), alkane synthesis (aar encoding acyl-ACP reductase, AAR), and recycling of free fatty acid (FFA) (aas encoding acyl-acyl carrier protein synthetase, AAS) in the unicellular cyanobacterium Synechocystis sp. PCC 6803. Results: To enhance lipid production, engineered strains were successfully obtained including an aas-overexpressing strain (OXAas), an aas-overexpressing strain with aar knockout (OXAas/KOAar), and an accDACB-overexpressing strain with lipA knockout (OXAccDACB/KOLipA). All engineered strains grew slightly slower than wild-type (WT), as well as with reduced levels of intracellular pigment levels of chlorophyll a and carotenoids. A higher lipid content was noted in all the engineered strains compared to WT cells, especially in OXAas, with maximal content and production rate of 34.5% w/DCW and 41.4 mg/L/day, respectively, during growth phase at day 4. The OXAccDACB/KOLipA strain, with an impediment of phospholipid hydrolysis to FFA, also showed a similarly high content of total lipid of about 32.5% w/ DCW but a lower production rate of 31.5 mg/L/day due to a reduced cell growth. The knockout interruptions generated, upon a downstream flow from intermediate fatty acyl-ACP, an induced unsaturated lipid production as observed in OXAas/KOAar and OXAccDACB/KOLipA strains with 5.4% and 3.1% w/DCW, respectively. Conclusions: Among the three metabolically engineered Synechocystis strains, the OXAas with enhanced free fatty acid recycling had the highest efficiency to increase lipid production.
Optimal energy and redox metabolism in the cyanobacterium Synechocystis sp. PCC 6803
bioRxiv (Cold Spring Harbor Laboratory), 2022
Cyanobacteria represent an attractive platform for the sustainable production of chemicals and fuels. However, the obtained rates, yields, and titers are below those required for commercial application. Carbon metabolism alone cannot achieve maximal accumulation of end-products, since an efficient production of target molecules entails energy and redox balance, in addition to carbon flow. The interplay between cofactor regeneration and heterologous metabolite overproduction in cyanobacteria is not fully explored. Here, we applied stoichiometric metabolic modelling of the cyanobacterium Synechocystis sp. PCC 6803, in order to investigate the optimality of energy and redox metabolism, while overproducing bio-alkenes-isobutene, isoprene, ethylene and 1-undecene. Our network-wide analysis indicates that the rate of NADP+ reduction, rather than ATP synthesis, controls ATP/NADPH ratio, and thereby chemical production. The simulation implies that energy and redox balance necessitates gluconeogenesis, and that acetate metabolism via phosphoketolase serves as an efficient carbon-and energy-recycling pathway. Furthermore, we show that an auxiliary pathway, composed of serine, one-carbon and glycine metabolism, supports cellular redox homeostasis and ATP cycling, and that the Synechocystis metabolism is controlled by few key reactions carrying a high flux. The study also revealed non-intuitive metabolic pathways to enhance isoprene, ethylene and 1-undecene production. We conclude that metabolism of ATP and NAD(P)H is entwined with carbon and nitrogen metabolism, and cannot be assessed in isolation. We envision that the presented here in-depth metabolic analysis will guide the a priori design of Synechocystis as a host strain for an efficient manufacturing of target products.
Optimal energy and redox metabolism in the cyanobacterium Synechocystis sp. PCC 6803
Cyanobacteria represent an attractive platform for the sustainable production of chemicals and fuels. However, the obtained rates, yields, and titers are below those required for commercial application. Carbon metabolism alone cannot achieve maximal accumulation of end-products, since an efficient production of target molecules entails energy and redox balance, in addition to carbon flow. The interplay between cofactor regeneration and heterologous metabolite overproduction in cyanobacteria is not fully explored. Here, we applied stoichiometric metabolic modelling of the cyanobacterium Synechocystis sp. PCC 6803, in order to investigate the optimality of energy and redox metabolism, while overproducing bio-alkenes - isobutene, isoprene, ethylene and 1-undecene. Our network-wide analysis indicates that the rate of NADP+ reduction, rather than ATP synthesis, controls ATP/NADPH ratio, and thereby chemical production. The simulation implies that energy and redox balance necessitates glu...
Photoautotrophic Polyhydroxyalkanoate Production in Cyanobacteria
Cyanobacteria: Omics and Manipulation, 2017
In this era of the 'Green Planet', cyanobacteria are ideally placed for exploitation as microbial cell factories, both for carbon capture and storage and for the sustainable production of secondary metabolites and biofuels. The application of omics technologies to cyanobacterial research has yielded a wealth of new information. However for today's busy researchers, trawling through the literature to stay abreast of current developments can be extremely time-consuming. By compiling and summarising the most important topics on cyanobacterial omics and manipulation, the authors of this book provide the reader with a timely overview of the field. Topics covered: The cyanobacterial core-genome with a focus on secondary metabolites; cyanobacterial evolution; genomics of NRPS/PKS biosynthetic gene clusters; RNA-seq based transcriptomic analysis of single cyanobacterial cells; transcriptomics of the responses: genes, sensors, and molecular triggers; transcriptomic and proteomic analysis of diurnal cycles in nitrogen-fixing cyanobacteria; proteomic analysis of post translational modifications; metabolic engineering and systems biology for free fatty acid production; isoprene production; ethanol production: impact of omics of the model organism Synechocystis on yield enhancement; engineering of alkane production; photoautotrophic polyhydroxyalkanoate production. This cutting-edge text will serve as a valuable resource for all those working in this field and is recommended for all microbiology libraries. Chapter 1. The Cyanobacterial Core-genome: Global and Specific Features with a Focus on Secondary Metabolites (Stefan Simm, Enrico Schleiff and Rafael Pernil) Chapter 2. Genome-wide Analysis of Cyanobacterial Evolution: The Example of Synechococcus (Petr Dvorák) Chapter 3. Genomics of NRPS/PKS Biosynthetic Gene Clusters in Cyanobacteria (Claire Pancrace, Muriel Gugger and Alexandra Calteau) Chapter 4. RNA-seq Based Transcriptomic Analysis of Single Cyanobacterial Cells
Scientific Reports
Cyanobacteria, a group of photosynthetic prokaryotes, are attractive hosts for biotechnological applications. It is envisaged that future biorefineries will deploy engineered cyanobacteria for the conversion of carbon dioxide to useful chemicals via light-driven, endergonic reactions. Fast-growing, genetically amenable, and stress-tolerant cyanobacteria are desirable as chassis for such applications. The recently reported strains such as Synechococcus elongatus UTEX 2973 and PCC 11801 hold promise, but additional strains may be needed for the ongoing efforts of metabolic engineering. Here, we report a novel, fast-growing, and naturally transformable cyanobacterium, S. elongatus PCC 11802, that shares 97% genome identity with its closest neighbor S. elongatus PCC 11801. The new isolate has a doubling time of 2.8 h at 1% CO2, 1000 µmole photons.m−2.s−1 and grows faster under high CO2 and temperature compared to PCC 11801 thus making it an attractive host for outdoor cultivations and e...