If cellulose can be effectively hydrolyzed intoglucose by cellulase,the production costs of hydrogen,ethanol or other chemicals from cellulosic materials will begreatly decreased,and economically viable production ofbiohydrogen and bioethanol will become feasible.Celluloseis degraded into glucoses by multi-component enzymesystems.Nowadays cellulases are widely used in brewing,food,bioenergy,fodder,textiles,paper,pharmaceuticals,environmental protection and other industries.However,existing cellulases have several problems that limit theirwider applications,including the low turnover number forsolid cellulosic materials,and low stability in adapting tovarious application conditions.For example,high temperature,low pH,and so on.Application of directedevolution technology may be one of the most effectiveways for improving the characteristics of cellulases.Thispaper presents a brief review of the cellulases hydrolysismechanism by cellulase,advances in cellulases(endoglucanaseandβ-glucosidase)improvement by directedevolution for several characteristics(for instance,thermalstability,pH adaptability and enzyme activity),limitationsof directed evolution for cellulases,and the outlook fordirected evolution for cellulase.
Five individual pretreatment methods, including three widely-used protocols （heat, acid and base） and two novel attempts （ultrasonic and ultraviolet）, were conducted in batch tests to compare their effects on mixed microflora to enhance hydrogen （H2） production from corn stover hydrolysate. Experimental results indicated that heat and base pretreatments significantly increased H2 yield with the values of 5.03 and 4.45 mmol H2/g sugar utilized, respectively, followed by acid pretreatment of 3.21 mmol H2/g sugar utilized. However, compared with the control （2.70 mmol H2/g sugar utilized）, ultrasonic and ultraviolet pretreatments caused indistinctive effects on H2 production with the values of 2.92 and 2.87 mmol H2/g sugar utilized, respectively. The changes of soluble metabolites composition caused by pretreatment were in accordance with H2-producing behavior. Concretely, more acetate accumulation and less ethanol production were found in pretreated processes, meaning that more reduced nicotinamide adenine dinucleotide （NADH） might be saved and flowed into H2-producing pathways. PCR-DGGE analysis indicated that the pretreatment led to the enrichment of some species, which appeared in large amounts and even dominated the microbial community. Most of the dominated species were affiliated to Enterobacter spp. and Escherichia spp. As another efflcient H2 producer, Clostridium bifermentan was only found in a large quantity after heat pretreatment. This strain might be mainly responsible for better performance of H2 production in this case.
Kun ZhangNanqi RenChanghong GuoAijie WangGuangli Cao
This study is aiming at investigating the metabolic characteristics of Ethanoligenens Harbinense YUAN-3.The effects of yeast extract powder and supplemental vitamins on the growth medium were assessed.With yeast powder as the sole nitrogen source,the biomass yield and hydrogen-producing capacity of YUAN-3 from glucose fermentation significantly increased.Adding vitamin in yeast powder can enhance hydrogen yield compared with no adding.Therefore vitamin supplement can be considered as an effective growth factor in this study.Batch culture also produced larger yields of hydrogen.
