Abstract
BackgroundLaminarin is a potential biomass feedstock for the production of glucose, which is the most preferable fermentable sugar in many microorganisms by which it can be converted to biofuels and bio-based chemicals. Also, laminarin is a good resource as functional materials because it consists of β-1,3-glucosidic linkages in its backbone and β-1,6-glucosidic linkages in its branches so that its oligosaccharides driven from laminarin have a variety of biological activities. It is industrially important to be able to produce laminarioligosaccharides as well as glucose from laminarin by a single enzyme because the enzyme cost accounts for a large part of bio-based products. In this study, we investigated the industrial applicability of Bgl1B, a unique β-glucosidase from Saccharophagus degradans 2-40T, belonging to the glycoside hydrolase family 1 (GH1) by characterizing its activity of hydrolyzing laminarin under various conditions.ResultsBgl1B was cloned and overexpressed in Escherichia coli from S. degradans 2-40T, and its enzymatic activity was characterized. Similar to most of β-glucosidases in GH1, Bgl1B was able to hydrolyze a variety of disaccharides having different β-linkages, such as laminaribiose, cellobiose, gentiobiose, lactose, and agarobiose, by cleaving β-1,3-, β-1,4-, and β-1,6-glycosidic linkages. However, Bgl1B showed the highest specific activity toward laminaribiose with a β-1,3-glycosidic linkage. In addition, it was able to hydrolyze laminarin, one of the major polysaccharides in brown macroalgae, into glucose with a conversion yield of 75% of theoretical maximum. Bgl1B also showed transglycosylation activity by producing oligosaccharides from laminarin and laminaribiose under a high mass ratio of substrate to enzyme. Furthermore, Bgl1B was found to be psychrophilic, exhibiting relative activity of 59–85% in the low-temperature range of 2–20 °C.ConclusionsBgl1B can directly hydrolyze laminarin into glucose with a high conversion yield without leaving any oligosaccharides. Bgl1B can exhibit high enzymatic activity in a broad range of low temperatures (2–20 °C), which is advantageous for establishing energy-efficient bioprocesses. In addition, under high substrate to enzyme ratios, Bgl1B can produce high-value laminarioligosaccharides via its transglycosylation activity. These results show that Bgl1B can be an industrially important enzyme for the production of biofuels and bio-based chemicals from brown macroalgae.
Highlights
Laminarin is a potential biomass feedstock for the production of glucose, which is the most prefer‐ able fermentable sugar in many microorganisms by which it can be converted to biofuels and bio-based chemicals
Because laminarin is composed of glucose, it is an ideal substrate from macroalgal biomass for producing glucose as a fermentable sugar
Laminarin, a polysaccharide composed of glucose, can be an important resource for glucose which can be converted to biofuels and bio-based chemicals by microorganisms
Summary
Laminarin is a potential biomass feedstock for the production of glucose, which is the most prefer‐ able fermentable sugar in many microorganisms by which it can be converted to biofuels and bio-based chemicals. Bgl1B showed transglycosyla‐ tion activity by producing oligosaccharides from laminarin and laminaribiose under a high mass ratio of substrate to enzyme. The main carbohydrate components of brown macroalgae are alginate and glucan, and glucan mainly occurs as laminarin, a glucose polysaccharide with β-1,3glucosidic linkages in its backbone and β-1,6-glucosidic linkages in its branches [3]. There have been many studies on the utilization of brown macroalgae as feedstocks for the production of bio-based chemicals [5,6,7], most of them are related to depolymerization of alginate, not laminarin. It is necessary to construct a simple and efficient enzymatic saccharification system to produce glucose from laminarin
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