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Induction of D-xylose uptake and expression of NAD(P)H-linked xylose reductase and NADP + -linked xylitol dehydrogenase in the oleaginous microalga Chlorella sorokiniana.

Zheng Y, Yu X, Li T, Xiong X, Chen S - Biotechnol Biofuels (2014)

Bottom Line: The uptake of D-xylose activated the related metabolic pathway, and the activities of a NAD(P)H-linked xylose reductase (XR) and a unique NADP(+)-linked xylitol dehydrogenase (XDH) were detected in C. sorokiniana.The uptake of D-xylose subsequently activated the expression of key catalytic enzymes that enabled D-xylose entering central metabolism.Results of this research are useful to better understand the D-xylose metabolic pathway in the microalga C. sorokiniana and provide a target for genetic engineering to improve D-xylose utilization for microalgal lipid production.

View Article: PubMed Central - PubMed

Affiliation: LJ Smith 258, Biological Systems Engineering, Washington State University, Pullman, WA 99164 USA.

ABSTRACT

Background: The heterotrophic and mixotrophic culture of oleaginous microalgae is a promising process to produce biofuel feedstock due to the advantage of fast growth. Various organic carbons have been explored for this application. However, despite being one of the most abundant and economical sugar resources in nature, D-xylose has never been demonstrated as a carbon source for wild-type microalgae. The purpose of the present work was to identify the feasibility of D-xylose utilization by the oleaginous microalga Chlorella sorokiniana.

Results: The sugar uptake kinetic analysis was performed with (14)C-labeled sugars and the data showed that the D-glucose induced algal cells (the alga was heterotrophically grown on D-glucose and then harvested as D-glucose induced cells) exhibited a remarkably increased D-xylose uptake rate. The maximum D-xylose transport rate was 3.8 nmol min(-1) mg(-1) dry cell weight (DCW) with K m value of 6.8 mM. D-xylose uptake was suppressed in the presence of D-glucose, D-galactose and D-fructose but not L-arabinose and D-ribose. The uptake of D-xylose activated the related metabolic pathway, and the activities of a NAD(P)H-linked xylose reductase (XR) and a unique NADP(+)-linked xylitol dehydrogenase (XDH) were detected in C. sorokiniana. Compared with the culture in the dark, the consumption of D-xylose increased 2 fold under light but decreased to the same level with addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), indicating that extra chemical energy from the light-dependent reaction contributed the catabolism of D-xylose for C. sorokiniana.

Conclusions: An inducible D-xylose transportation system and a related metabolic pathway were discovered for microalga for the first time. The transportation of D-xylose across the cell membrane of C. sorokiniana could be realized by an inducible hexose symporter. The uptake of D-xylose subsequently activated the expression of key catalytic enzymes that enabled D-xylose entering central metabolism. Results of this research are useful to better understand the D-xylose metabolic pathway in the microalga C. sorokiniana and provide a target for genetic engineering to improve D-xylose utilization for microalgal lipid production.

No MeSH data available.


Related in: MedlinePlus

Effect of pH (A) and temperature (B) on the activity of XR (circle) and XDH (triangle) present in crude cell-free extract obtained from inducedC. sorokiniana. The induced algal cells were washed with sterile distilled water and re-suspended in 8 mg DCW per mL in 50 mL minimal medium supplemented with 5 mM KNO 3 and 40 mM D-xylose under light for 24 hours.
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Fig2: Effect of pH (A) and temperature (B) on the activity of XR (circle) and XDH (triangle) present in crude cell-free extract obtained from inducedC. sorokiniana. The induced algal cells were washed with sterile distilled water and re-suspended in 8 mg DCW per mL in 50 mL minimal medium supplemented with 5 mM KNO 3 and 40 mM D-xylose under light for 24 hours.

Mentions: Figure 2 shows the effects of pH and temperature on the activity of XR and XDH, present in crude cell-free extract obtained from the induced C. sorokiniana after incubation with D-xylose. The activity of XR increased from 0.018 to 0.021 U mg−1 protein with an increase in pH from 5.5 to 6.0, followed by a decrease to 0.012 U mg−1 protein at pH 9.0. In the same pH range tested, XDH achieved the highest activity of 0.026 U mg−1 protein at pH 8.0. At pH 6.0 (the optimal pH for XR), the activity of XDH decreased 92% from its highest value. Meanwhile, a loss of only 30% was observed on XR activity at pH 8.0 (the optimal pH for XDH). Therefore, an acidic environment was more detrimental to XDH than the negative effect of alkalinity to XR. The optimal temperature for XDH was 50°C and further increasing the temperature to 70°C resulted in an activity loss of 93%. XR was more stable at higher temperature than XDH. The elevated temperature improved the performance of XR and the highest activity of 0.027 U mg−1 protein was obtained at 70°C.Figure 2


Induction of D-xylose uptake and expression of NAD(P)H-linked xylose reductase and NADP + -linked xylitol dehydrogenase in the oleaginous microalga Chlorella sorokiniana.

Zheng Y, Yu X, Li T, Xiong X, Chen S - Biotechnol Biofuels (2014)

Effect of pH (A) and temperature (B) on the activity of XR (circle) and XDH (triangle) present in crude cell-free extract obtained from inducedC. sorokiniana. The induced algal cells were washed with sterile distilled water and re-suspended in 8 mg DCW per mL in 50 mL minimal medium supplemented with 5 mM KNO 3 and 40 mM D-xylose under light for 24 hours.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4195881&req=5

Fig2: Effect of pH (A) and temperature (B) on the activity of XR (circle) and XDH (triangle) present in crude cell-free extract obtained from inducedC. sorokiniana. The induced algal cells were washed with sterile distilled water and re-suspended in 8 mg DCW per mL in 50 mL minimal medium supplemented with 5 mM KNO 3 and 40 mM D-xylose under light for 24 hours.
Mentions: Figure 2 shows the effects of pH and temperature on the activity of XR and XDH, present in crude cell-free extract obtained from the induced C. sorokiniana after incubation with D-xylose. The activity of XR increased from 0.018 to 0.021 U mg−1 protein with an increase in pH from 5.5 to 6.0, followed by a decrease to 0.012 U mg−1 protein at pH 9.0. In the same pH range tested, XDH achieved the highest activity of 0.026 U mg−1 protein at pH 8.0. At pH 6.0 (the optimal pH for XR), the activity of XDH decreased 92% from its highest value. Meanwhile, a loss of only 30% was observed on XR activity at pH 8.0 (the optimal pH for XDH). Therefore, an acidic environment was more detrimental to XDH than the negative effect of alkalinity to XR. The optimal temperature for XDH was 50°C and further increasing the temperature to 70°C resulted in an activity loss of 93%. XR was more stable at higher temperature than XDH. The elevated temperature improved the performance of XR and the highest activity of 0.027 U mg−1 protein was obtained at 70°C.Figure 2

Bottom Line: The uptake of D-xylose activated the related metabolic pathway, and the activities of a NAD(P)H-linked xylose reductase (XR) and a unique NADP(+)-linked xylitol dehydrogenase (XDH) were detected in C. sorokiniana.The uptake of D-xylose subsequently activated the expression of key catalytic enzymes that enabled D-xylose entering central metabolism.Results of this research are useful to better understand the D-xylose metabolic pathway in the microalga C. sorokiniana and provide a target for genetic engineering to improve D-xylose utilization for microalgal lipid production.

View Article: PubMed Central - PubMed

Affiliation: LJ Smith 258, Biological Systems Engineering, Washington State University, Pullman, WA 99164 USA.

ABSTRACT

Background: The heterotrophic and mixotrophic culture of oleaginous microalgae is a promising process to produce biofuel feedstock due to the advantage of fast growth. Various organic carbons have been explored for this application. However, despite being one of the most abundant and economical sugar resources in nature, D-xylose has never been demonstrated as a carbon source for wild-type microalgae. The purpose of the present work was to identify the feasibility of D-xylose utilization by the oleaginous microalga Chlorella sorokiniana.

Results: The sugar uptake kinetic analysis was performed with (14)C-labeled sugars and the data showed that the D-glucose induced algal cells (the alga was heterotrophically grown on D-glucose and then harvested as D-glucose induced cells) exhibited a remarkably increased D-xylose uptake rate. The maximum D-xylose transport rate was 3.8 nmol min(-1) mg(-1) dry cell weight (DCW) with K m value of 6.8 mM. D-xylose uptake was suppressed in the presence of D-glucose, D-galactose and D-fructose but not L-arabinose and D-ribose. The uptake of D-xylose activated the related metabolic pathway, and the activities of a NAD(P)H-linked xylose reductase (XR) and a unique NADP(+)-linked xylitol dehydrogenase (XDH) were detected in C. sorokiniana. Compared with the culture in the dark, the consumption of D-xylose increased 2 fold under light but decreased to the same level with addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), indicating that extra chemical energy from the light-dependent reaction contributed the catabolism of D-xylose for C. sorokiniana.

Conclusions: An inducible D-xylose transportation system and a related metabolic pathway were discovered for microalga for the first time. The transportation of D-xylose across the cell membrane of C. sorokiniana could be realized by an inducible hexose symporter. The uptake of D-xylose subsequently activated the expression of key catalytic enzymes that enabled D-xylose entering central metabolism. Results of this research are useful to better understand the D-xylose metabolic pathway in the microalga C. sorokiniana and provide a target for genetic engineering to improve D-xylose utilization for microalgal lipid production.

No MeSH data available.


Related in: MedlinePlus