Engineered xylose utilization enhances bio-products productivity in the cyanobacterium Synechocystis sp. PCC 6803

Abstract

Hydrolysis of plant biomass generates a mixture of simple sugars that is particularly rich in glucose and xylose. Fermentation of the released sugars emits CO2 as byproduct due to metabolic inefficiencies. Therefore, the ability of a microbe to simultaneously convert biomass sugars and photosynthetically fix CO2 into target products is very desirable. In this work, the cyanobacterium, Synechocystis 6803, was engineered to grow on xylose in addition to glucose. Both the xylA (xylose isomerase) and xylB (xylulokinase) genes from Escherichia coli were required to confer xylose utilization, but a xylose-specific transporter was not required. Introduction of xylAB into an ethylene-producing strain increased the rate of ethylene production in the presence of xylose. Additionally, introduction of xylAB into a glycogen-synthesis mutant enhanced production of keto acids. Isotopic tracer studies found that nearly half of the carbon in the excreted keto acids was derived from the engineered xylose metabolism, while the remainder was derived from CO2 fixation.

Uncovering Potential Applications of Cyanobacteria and Algal Metabolites in Biology, Agriculture and Medicine: Current Status and Future Prospects

“…The production of ethylene, an important component of polymers has been enhanced by engineering the Synechococcus elongatus PCC 7942 and Synechocystis sp. PCC 6803 and the production was improved by 64% (0.9 mg/L/h; Takahama et al, 2003; Ungerer et al, 2012; Lee et al, 2015). As the need of biofuel production is increasing, therefore, to optimize free fatty acids production in Synechococcus elongatus PCC 7942 and Synechocystis sp.…”

2,3 Butanediol production in an obligate photoautotrophic cyanobacterium in dark conditions via diverse sugar consumption

“…In lactic acid production, glucose supplementation 84 resulted in no improvement in productivity or titer. More recently, Synechocystis has 85 been engineered to consume xylose in addition to the native substrate, glucose, for 86 augmentation of heterologous ethylene production (Lee et al, 2015). This strain showed 87 increased growth in heterotrophic (dark) conditions as well as up to 1.6 fold increase in 88 mixotrophic (lighted) ethylene production compared to strictly photoautotrophic growth 89 and production.…”

Cyanobacterial chemical production

“…Further improvement came from the use of oleyl alcohol as a solvent trap to relieve toxicity and increased the isobutanol titer to 298 mg/L (Varman et al, 2013a). This approach of improving sugar consumption in cyanobacteria has also been investigated for ethylene production in (Lee et al, 2015). Two genes for…”

“…Titer/ Productivity Host Additional carbon source Reference 2-methyl-1-butanol 0.2 g/L 7942 (Shen and Liao, 2012) Isopropanol 0.1 g/L 7942 (Hirokawa et al, 2015) 23BDO 2.4 g/L 7942 (Oliver et al, 2013) 23BDO 3 g/L 7942 glucose (McEwen et al, 2016) Fatty alcohols 3 mg/gDCW 6803 (Yao et al, 2014) Ethanol 2.3 g/L 6803 (Luan et al, 2015) 3HB 0.5 g/L 6803 (Wang et al, 2013a) 3HP 0.7 g/L 7942 (Lan et al, 2015) P3HB 5 % DCW 7002 P3H4HB 4.5% DCW 7002 Ethylene 5.7 mL/L/h 6803 (Ungerer et al, 2012) Ethylene 0.9 mL/L/h 6803 xylose (Lee et al, 2015) Heptadecane 4 µg/gDCW 15041c (Yoshino et al, 2015) Free fatty acids 0.2 g/L 6803 (Liu et al, 2011) Sucrose 0.1 g/L 7942 (Ducat et al, 2012) Sucrose 0.1 g/L 6803 (Du et al, 2013) GG 0.3 g/L 6803 (Tan et al, 2015) Squalene 0.7 mg/OD/L 6803 (Englund et al, 2014) 13R-manoyl oxide 0.5 mg/gDCW 6803 (Englund et al, 2015) Farnesene 70 µg/L/OD/day 7120 (Halfmann et al, 2014) Isoprene 0.3 mg/gDCW 6803 (Bentley et al, 2014) Lactic acid 0.8 g/L 6803 (Angermayr et al, 2014) Lactic acid 2.2 g/L 6803 acetate (Varman et al, 2013b) Isobutanol 0.3 g/L 6803 glucose (Varman et al, 2013a)…”