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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

Proposed D-xylose metabolic pathway in the green microalgaC. sorokiniana. D-xylose is transported across the cell membrane through the inducible hexose symporter. The uptake of D-xylose activates the expression of NADPH-linked XR and NADP + -linked XDH, which converts D-xylose to D-xylulose and enters the PPP pathway after catalyzing to D-xylulose 5-P. NADPH generated during the first stage of photosynthesis from light energy serves as the coenzyme for D-xylose metabolism. DCMU negatively affects the improvement of D-xylose catabolism from the light-dependent reaction by blocking electron flow from photosystem II (PSII) to photosystem I (PSI) and inhibiting NADPH production.
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Fig4: Proposed D-xylose metabolic pathway in the green microalgaC. sorokiniana. D-xylose is transported across the cell membrane through the inducible hexose symporter. The uptake of D-xylose activates the expression of NADPH-linked XR and NADP + -linked XDH, which converts D-xylose to D-xylulose and enters the PPP pathway after catalyzing to D-xylulose 5-P. NADPH generated during the first stage of photosynthesis from light energy serves as the coenzyme for D-xylose metabolism. DCMU negatively affects the improvement of D-xylose catabolism from the light-dependent reaction by blocking electron flow from photosystem II (PSII) to photosystem I (PSI) and inhibiting NADPH production.

Mentions: Our results showed that C. sorokiniana could take up D-xylose through a single-carrier system. The maximum D-xylose transport rate of 3.8 nmol min−1 mg−1 DCW with Km value of 6.8 mM was obtained in D-glucose induced C. sorokiniana. It has been reported that Chlorella cells possess an inducible active hexose/H+ symport system responsible for uptake of D-glucose from the environment [12]. Similar with the D-xylose-metabolizing microbes, the green microalga C. sorokiniana might share the inducible hexose symporter for D-xylose uptake (Figure 4). However, D-glucose strongly inhibits D-xylose transportation due to the different affinities for these two sugars [21]. Our results demonstrated that D-xylose uptake was suppressed in the presence of D-glucose, D-galactose and D-fructose, but the degrees of inhibition were different due to the different affinities to these hexoses. C. sorokiniana might not be able to transport the pentose sugars (L-arabinose and D-ribose) by using the hexose symporter, because no significant inhibitory effect on D-xylose assimilation was observed for these sugars.Figure 4


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)

Proposed D-xylose metabolic pathway in the green microalgaC. sorokiniana. D-xylose is transported across the cell membrane through the inducible hexose symporter. The uptake of D-xylose activates the expression of NADPH-linked XR and NADP + -linked XDH, which converts D-xylose to D-xylulose and enters the PPP pathway after catalyzing to D-xylulose 5-P. NADPH generated during the first stage of photosynthesis from light energy serves as the coenzyme for D-xylose metabolism. DCMU negatively affects the improvement of D-xylose catabolism from the light-dependent reaction by blocking electron flow from photosystem II (PSII) to photosystem I (PSI) and inhibiting NADPH production.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig4: Proposed D-xylose metabolic pathway in the green microalgaC. sorokiniana. D-xylose is transported across the cell membrane through the inducible hexose symporter. The uptake of D-xylose activates the expression of NADPH-linked XR and NADP + -linked XDH, which converts D-xylose to D-xylulose and enters the PPP pathway after catalyzing to D-xylulose 5-P. NADPH generated during the first stage of photosynthesis from light energy serves as the coenzyme for D-xylose metabolism. DCMU negatively affects the improvement of D-xylose catabolism from the light-dependent reaction by blocking electron flow from photosystem II (PSII) to photosystem I (PSI) and inhibiting NADPH production.
Mentions: Our results showed that C. sorokiniana could take up D-xylose through a single-carrier system. The maximum D-xylose transport rate of 3.8 nmol min−1 mg−1 DCW with Km value of 6.8 mM was obtained in D-glucose induced C. sorokiniana. It has been reported that Chlorella cells possess an inducible active hexose/H+ symport system responsible for uptake of D-glucose from the environment [12]. Similar with the D-xylose-metabolizing microbes, the green microalga C. sorokiniana might share the inducible hexose symporter for D-xylose uptake (Figure 4). However, D-glucose strongly inhibits D-xylose transportation due to the different affinities for these two sugars [21]. Our results demonstrated that D-xylose uptake was suppressed in the presence of D-glucose, D-galactose and D-fructose, but the degrees of inhibition were different due to the different affinities to these hexoses. C. sorokiniana might not be able to transport the pentose sugars (L-arabinose and D-ribose) by using the hexose symporter, because no significant inhibitory effect on D-xylose assimilation was observed for these sugars.Figure 4

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