Engineering of a Cellulolytic Bacterium and a Lignocellulose-degrading Enzyme for Utilization of Cellulosic Biomass
For sustainable development of human societies, we should produce the products such as biofuel from renewable and environmentally-friendly materials instead of petroleum. Cellulosic biomass is a candidate material for the biofuel production. To achieve commercial biofuel production from cellulosic biomass, the significant cost reduction is required. Here I proposed the biofuel production strategy in which a cellulolytic bacterium degrades cellulosic biomass and produces fuel compounds, simultaneously. Enzymatic degradation of cellulosic biomass is the costly process in the biofuel production. To understand the detail feature of the enzymatic degradation of cellulosic biomass, one of the most powerful lignocellulose-degrading enzyme produced from a cellulolytic bacterium was characterized. The lignocellulose-degrading enzyme harbor a carbohydrate-binding module, which is used to determine the binding character of the enzyme in this study. I report the binding characters at the molecular level: the carbohydrate-binding module binds to various components of cellulosic biomass such as crystalline and non-crystalline form of cellulose, and xyloglucan. Few researchers have reported the examples of engineering of lignocellulose-degrading enzymes for improvement of the degradation ability of cellulosic biomass so far. Here, I show that the engineered lignocellulose-degrading enzyme with the replacement of carbohydrate-binding modules changed the specificity of the activity. Additionally, I also showed that the engineered enzyme could efficiently degrade a cellulosic biomass, milled corn hull, than the original enzyme, suggesting the possibility that the replacement of carbohydrate-binding modules will be one of the ways to improve the degradation ability of lignocellulose-degrading enzymes for cellulosic biomass. Some cellulolytic bacteria produce water-soluble fuel compounds such as ethanol. To collect water-soluble fuel compounds from the culture broth, a distillation step is required, which also significantly increases the cost of biofuel production. In contrast to the water-soluble fuel compounds, it is expected that water-insoluble compounds such as higher alcohols are more easily collected from the culture broth by phase separation due to their insolubility in water. Here I report that the engineered cellulolytic bacterium produced higher alcohols from cellulose in which the costly processes, the supplementation of lignocellulose-degrading enzymes and distillation of fuel compounds, were eliminated. These results in the characterization and the engineering of lignocellulose-degrading enzyme and cellulolytic bacteria in this study will be basic information of process developments for the further cost reduction of the biofuel production, resulting the establishment of economic biofuel production from cellulosic biomass.
Doctoral Dissertation / 博士論文
本文 / Laboratory of Food Chemistry and Biomass Graduate School of Regional Innovation Studies, Mie University, Japan