Abstract
Current cellulosic biomass hydrolysis is based on the one-time use of cellulases. Cellulases immobilized on magnetic nanocarriers offer the advantages of magnetic separation and repeated use for continuous hydrolysis. Most immobilization methods focus on only one type of cellulase. Here, we report co-immobilization of two types of cellulases, β-glucosidase A (BglA) and cellobiohydrolase D (CelD), on sub-20 nm superparamagnetic nanoparticles. The nanoparticles demonstrated 100% immobilization efficiency for both BglA and CelD. The total enzyme activities of immobilized BglA and CelD were up to 67.1% and 41.5% of that of the free cellulases, respectively. The immobilized BglA and CelD each retained about 85% and 43% of the initial immobilized enzyme activities after being recycled 3 and 10 times, respectively. The effects of pH and temperature on the immobilized cellulases were also investigated. Co-immobilization of BglA and CelD on MNPs is a promising strategy to promote synergistic action of cellulases while lowering enzyme consumption.
Highlights
Cellulosic biomass, serving as a renewable carbon and energy source, provides a significantly large amount of feedstock for producing sugars
We demonstrate simultaneous immobilization of cellobiohydrolase D (CelD) and β-glucosidase A (BglA) on sub-20 nm superparamagnetic nanoparticles (Figure 1)
The average diameter of the naked magnetic nanoparticles (MNPs) was measured to be 7.7 nm based on transmission electron microscope (TEM) (Figure 2a), which was smaller than the superparamagnetic critical size of iron oxide particles (20 nm) [22]
Summary
Cellulosic biomass, serving as a renewable carbon and energy source, provides a significantly large amount of feedstock for producing sugars. These sugars can be biochemically converted into desired metabolites, such as lactic acid, succinic acid, and levulinic acid, or biofuel, such as ethanol and butanol [1]. Cellulose can be decomposed into glucose by the synergistic action of three types of enzymes: endo-glucanase, cellobiohydrolase, and β-glucosidase [3]. Endo-glucanase randomly breaks internal bonds of amorphous cellulose to expose individual cellulose polysaccharide chains. Cellobiohydrolase cleaves 2–4 units from the end of the exposed chains, producing tetrasaccharides and disaccharides such as cellobiose. These cellulases are produced by various bacteria, fungi, and plants [1]
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