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Untreated Chlorella homosphaera biomass allows for high rates of cell wall glucan enzymatic hydrolysis when using exoglucanase-free cellulases.

Rodrigues MA, Teixeira RS, Ferreira-Leitão VS, da Silva Bon EP - Biotechnol Biofuels (2015)

Bottom Line: The initial hydrolysis rates when using A. cellulolyticus or T. reesei enzymes were significantly lower, whereas the results for the T. reesei-A. awamori and A. awamori-A. cellulolyticus blends were similar to that for the A. awamori enzymes.High rates of enzymatic hydrolysis were achieved for untreated C. homosphaera biomass with enzymes containing endoglucanase and β-glucosidase activities and devoid of cellobiohydrolase activity.These findings simplify the complexity of the enzyme pools required for the enzymatic hydrolysis of microalgal biomass decreasing the enzyme cost for the production of microalgae-derived glucose syrups.

View Article: PubMed Central - PubMed

Affiliation: Federal University of Rio de Janeiro, Institute of Chemistry, Department of Biochemistry, Applied Photosynthesis Laboratory, Athos Avenida da Silveria Ramos, 149-Technology Centre, Block A, Room 532, University City, Rio de Janeiro, RJ 21941-909 Brazil.

ABSTRACT

Background: Chlorophyte microalgae have a cell wall containing a large quantity of cellulose Iα with a triclinic unit cell hydrogen-bonding pattern that is more susceptible to hydrolysis than that of the cellulose Iβ polymorphic form that is predominant in higher plants. This study addressed the enzymatic hydrolysis of untreated Chlorella homosphaera biomass using selected enzyme preparations, aiming to identify the relevant activity profile for the microalgae cellulose hydrolysis. Enzymes from Acremonium cellulolyticus, which secretes a complete pool of cellulases plus β-glucosidase; Trichoderma reesei, which secretes a complete pool of cellulases with low β-glucosidase; Aspergillus awamori, which secretes endoglucanases and β-glucosidase; blends of T. reesei-A. awamori or A. awamori-A. cellulolyticus enzymes; and a purified A. awamori β-glucosidase were evaluated.

Results: The highest initial glucan hydrolysis rate of 140.3 mg/g/h was observed for A. awamori enzymes with high β-glucosidase, low endoglucanase, and negligible cellobiohydrolase activities. The initial hydrolysis rates when using A. cellulolyticus or T. reesei enzymes were significantly lower, whereas the results for the T. reesei-A. awamori and A. awamori-A. cellulolyticus blends were similar to that for the A. awamori enzymes. Thus, the hydrolysis of C. homosphaera cellulose was performed exclusively by the endoglucanase and β-glucosidase activities. X-ray diffraction data showing negligible cellulose crystallinity for untreated C. homosphaera biomass corroborate these findings. The A. awamori-A. cellulolyticus blend showed the highest initial polysaccharide hydrolysis rate of 185.6 mg/g/h, as measured by glucose equivalent, in addition to the highest predicted maximum glucan hydrolysis yield of 47% of total glucose (w/w). T. reesei enzymes showed the lowest predicted maximum glucan hydrolysis yield of 25% (w/w), whereas the maximum yields of approximately 31% were observed for the other enzyme preparations. The hydrolysis yields were proportional to the enzyme β-glucosidase load, indicating that the endoglucanase load was not rate-limiting.

Conclusions: High rates of enzymatic hydrolysis were achieved for untreated C. homosphaera biomass with enzymes containing endoglucanase and β-glucosidase activities and devoid of cellobiohydrolase activity. These findings simplify the complexity of the enzyme pools required for the enzymatic hydrolysis of microalgal biomass decreasing the enzyme cost for the production of microalgae-derived glucose syrups.

No MeSH data available.


Scanning electron microscopy of groundC. homosphaerabiomass (A) before enzymatic hydrolysis and (B) after 48 h of enzymatic hydrolysis using theA. awamori-T. reeseiblend. Samples were adhered to carbon tape, sputter-coated with 28 nm gold using an Emitech/K550 model and observed via SEM as described in the Materials and methods section. Magnifications of × 1,200 (A) and × 6,000 (B) were chosen to show the action of the enzyme blend more clearly on C. homosphaera biomass. The scale bars represent 50 μm (A) and 10 μm (B).
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Fig6: Scanning electron microscopy of groundC. homosphaerabiomass (A) before enzymatic hydrolysis and (B) after 48 h of enzymatic hydrolysis using theA. awamori-T. reeseiblend. Samples were adhered to carbon tape, sputter-coated with 28 nm gold using an Emitech/K550 model and observed via SEM as described in the Materials and methods section. Magnifications of × 1,200 (A) and × 6,000 (B) were chosen to show the action of the enzyme blend more clearly on C. homosphaera biomass. The scale bars represent 50 μm (A) and 10 μm (B).

Mentions: Figure 6A shows the scanning electron microscopy of C. homosphaera cells and cell fragments that were dried and hand-milled, and Figure 6B shows the C. homosphaera cells after enzymatic hydrolysis when using the A. awamori-T. reesei enzyme blend. The images suggest that the enzyme action resulted in a more homogenous material and that an amorphous and sticky material that surrounded the undigested algae was removed by enzymatic hydrolysis.Figure 6


Untreated Chlorella homosphaera biomass allows for high rates of cell wall glucan enzymatic hydrolysis when using exoglucanase-free cellulases.

Rodrigues MA, Teixeira RS, Ferreira-Leitão VS, da Silva Bon EP - Biotechnol Biofuels (2015)

Scanning electron microscopy of groundC. homosphaerabiomass (A) before enzymatic hydrolysis and (B) after 48 h of enzymatic hydrolysis using theA. awamori-T. reeseiblend. Samples were adhered to carbon tape, sputter-coated with 28 nm gold using an Emitech/K550 model and observed via SEM as described in the Materials and methods section. Magnifications of × 1,200 (A) and × 6,000 (B) were chosen to show the action of the enzyme blend more clearly on C. homosphaera biomass. The scale bars represent 50 μm (A) and 10 μm (B).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4356055&req=5

Fig6: Scanning electron microscopy of groundC. homosphaerabiomass (A) before enzymatic hydrolysis and (B) after 48 h of enzymatic hydrolysis using theA. awamori-T. reeseiblend. Samples were adhered to carbon tape, sputter-coated with 28 nm gold using an Emitech/K550 model and observed via SEM as described in the Materials and methods section. Magnifications of × 1,200 (A) and × 6,000 (B) were chosen to show the action of the enzyme blend more clearly on C. homosphaera biomass. The scale bars represent 50 μm (A) and 10 μm (B).
Mentions: Figure 6A shows the scanning electron microscopy of C. homosphaera cells and cell fragments that were dried and hand-milled, and Figure 6B shows the C. homosphaera cells after enzymatic hydrolysis when using the A. awamori-T. reesei enzyme blend. The images suggest that the enzyme action resulted in a more homogenous material and that an amorphous and sticky material that surrounded the undigested algae was removed by enzymatic hydrolysis.Figure 6

Bottom Line: The initial hydrolysis rates when using A. cellulolyticus or T. reesei enzymes were significantly lower, whereas the results for the T. reesei-A. awamori and A. awamori-A. cellulolyticus blends were similar to that for the A. awamori enzymes.High rates of enzymatic hydrolysis were achieved for untreated C. homosphaera biomass with enzymes containing endoglucanase and β-glucosidase activities and devoid of cellobiohydrolase activity.These findings simplify the complexity of the enzyme pools required for the enzymatic hydrolysis of microalgal biomass decreasing the enzyme cost for the production of microalgae-derived glucose syrups.

View Article: PubMed Central - PubMed

Affiliation: Federal University of Rio de Janeiro, Institute of Chemistry, Department of Biochemistry, Applied Photosynthesis Laboratory, Athos Avenida da Silveria Ramos, 149-Technology Centre, Block A, Room 532, University City, Rio de Janeiro, RJ 21941-909 Brazil.

ABSTRACT

Background: Chlorophyte microalgae have a cell wall containing a large quantity of cellulose Iα with a triclinic unit cell hydrogen-bonding pattern that is more susceptible to hydrolysis than that of the cellulose Iβ polymorphic form that is predominant in higher plants. This study addressed the enzymatic hydrolysis of untreated Chlorella homosphaera biomass using selected enzyme preparations, aiming to identify the relevant activity profile for the microalgae cellulose hydrolysis. Enzymes from Acremonium cellulolyticus, which secretes a complete pool of cellulases plus β-glucosidase; Trichoderma reesei, which secretes a complete pool of cellulases with low β-glucosidase; Aspergillus awamori, which secretes endoglucanases and β-glucosidase; blends of T. reesei-A. awamori or A. awamori-A. cellulolyticus enzymes; and a purified A. awamori β-glucosidase were evaluated.

Results: The highest initial glucan hydrolysis rate of 140.3 mg/g/h was observed for A. awamori enzymes with high β-glucosidase, low endoglucanase, and negligible cellobiohydrolase activities. The initial hydrolysis rates when using A. cellulolyticus or T. reesei enzymes were significantly lower, whereas the results for the T. reesei-A. awamori and A. awamori-A. cellulolyticus blends were similar to that for the A. awamori enzymes. Thus, the hydrolysis of C. homosphaera cellulose was performed exclusively by the endoglucanase and β-glucosidase activities. X-ray diffraction data showing negligible cellulose crystallinity for untreated C. homosphaera biomass corroborate these findings. The A. awamori-A. cellulolyticus blend showed the highest initial polysaccharide hydrolysis rate of 185.6 mg/g/h, as measured by glucose equivalent, in addition to the highest predicted maximum glucan hydrolysis yield of 47% of total glucose (w/w). T. reesei enzymes showed the lowest predicted maximum glucan hydrolysis yield of 25% (w/w), whereas the maximum yields of approximately 31% were observed for the other enzyme preparations. The hydrolysis yields were proportional to the enzyme β-glucosidase load, indicating that the endoglucanase load was not rate-limiting.

Conclusions: High rates of enzymatic hydrolysis were achieved for untreated C. homosphaera biomass with enzymes containing endoglucanase and β-glucosidase activities and devoid of cellobiohydrolase activity. These findings simplify the complexity of the enzyme pools required for the enzymatic hydrolysis of microalgal biomass decreasing the enzyme cost for the production of microalgae-derived glucose syrups.

No MeSH data available.