Abstract
The aim of this work was to assess the possibility of using native bacterial nanocellulose (BC) as a carrier for laccase immobilization. BC was synthesized by Gluconacetobacter xylinus, which was statically cultivated in a mannitol-based medium and was freeze-dried to form BC sponge after purification. For the first time, fungal laccase from Trametes versicolor was immobilized on the native nanofibril network-structured BC sponge through physical adsorption and cross-linking with glutaraldehyde. The properties including morphologic and structural features of the BC as well as the immobilized enzyme were thoroughly investigated. It was found that enzyme immobilized by cross-linking exhibited broader pH operation range of high catalytic activity as well as higher running stability compared to free and adsorbed enzyme. Using ABTS as substrate, the optimum pH value was 3.5 for the adsorption-immobilized laccase and 4.0 for the crosslinking-immobilized laccase. The immobilized enzyme retained 69% of the original activity after being recycled seven times. Novel applications of the BC-immobilized enzyme tentatively include active packaging, construction of biosensors, and establishment of bioreactors.
Highlights
Laccase is a multi-copper oxidase that is widely distributed in plants and certain fungi (Reinhammar, 1997)
It could be seen that the bacterial nanocellulose (BC) membrane had a reticulated structure consisting of ultrafine cellulose fibrils with a diameter of less than 100 nm, which resulted in large surface area
The results showed that the average pore size, the pore volume and the surface area of the BC sponge were 11.5 nm, 0.25 cm3/g, and 72.2 m2/g, respectively
Summary
Laccase (benzenediol:oxygen oxidoreductase, EC 1.10.3.2) is a multi-copper oxidase that is widely distributed in plants and certain fungi (Reinhammar, 1997). Laccase catalyzes the one-electron oxidation of a variety of aromatic compounds, in particular phenols, as well as diamines and hexacyanoferrate, concomitantly with the four-electron reduction of molecular oxygen to water. In the presence of low-molecular mass mediators, laccase can be employed for the oxidation of a variety of non-phenolic aromatic compounds (Hong et al, 2006; Riva, 2006; Cañas and Camarero, 2010). Laccases have very broad substrate specificity with regard to the reducing substrate and have an interesting potential as industrial enzymes. Laccases are attracting considerable interest for a variety of biotechnological applications, such as in organic synthesis/transformation, textile processing, food industry, pharmaceutical industry, remediation of contaminated environments, delignification of pulp, modification of lignocellulosic materials, manufacture of new materials, as well as construction of biosensors and biofuel cells (Couto and Toca-Herrera, 2006; Munari et al, 2007; Rita et al, 2008; Litescu et al, 2010; Majeau et al, 2010; Kudanga et al, 2011).
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