Chang YC1, Choi D2, Takamizawa K3, Kikuchi S4.
Bioresour Technol. 2014;152:429-36.
1Division of Applied Sciences, College of Environmental Technology, Graduate School of Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran 050-8585, Hokkaido, Japan.
Electronic address: [email protected]
2Department of Pharmacy, College of Pharmacy, Chungbuk National University, Cheongju 361-763, Republic of Korea. Electronic address: [email protected]
3Department of Applied Life Science, Faculty of Applied Biological Sciences, Gifu University, Gifu 501-1193, Japan.
4Division of Applied Sciences, College of Environmental Technology, Graduate School of Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran 050-8585, Hokkaido, Japan.
Effective biological pretreatment method for enhancing cellulase performance was investigated. Two alkali lignin-degrading bacteria were isolated from forest soils in Japan and named CS-1 and CS-2. 16S rDNA sequence analysis indicated that CS-1 and CS-2 were Bacillus sp. Strains CS-1 and CS-2 displayed alkali lignin degradation capability. With initial concentrations of 0.05-2.0 g L(-1), at least 61% alkali lignin could be degraded within 48 h. High laccase activities were observed in crude enzyme extracts from the isolated strains. This result indicated that alkali lignin degradation was correlated with laccase activities. Judging from the net yields of sugars after enzymatic hydrolysis, the most effective pretreatment method for enhancing cellulase performance was a two-step processing procedure (pretreatment using Bacillus sp. CS-1 followed by lactic acid bacteria) at 68.6%. These results suggest that the two-step pretreatment procedure is effective at accelerating cellulase performance.
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Extensive research on the effective utilization of lignocellulosic material has been conducted. However, cost-effectively releasing sugars from recalcitrant lignocellulose hinders the economic production of cellulosic biofuels because of the low susceptibility of lignocellulose to hydrolysis, which is attributable to the crystalline structure of cellulose fibrils surrounded by hemicellulose and the presence of the lignin seal, which prevents penetration by degrading enzymes (Chahal PS, Chahal DS, Lignocellulose waste: biological conversion. In: Martin AM (ed) Bioconversion of waste materials to industrial products, 2nd end. Blackie Academic & Professional, London, pp. 376–422 (1998)). Therefore, an ideal pretreatment is needed to reduce the lignin content and crystallinity of cellulose, and increase the surface area of these materials (Wang et al., Appl. Biochem. Biotechnol. 51:70–72 (1998)).
We optimized biological pretreatment method focusing on the development of environmentally-friendly and low energy requirement method for the removal of lignin and enhancing cellulase performance. To increase the surface area accessible to cellulose resulting in hemicellulose elimination, from two lactic acid bacteria (Lactobacillus bulgaricus and Streptococcus thermophilus) was examined. Moreover, application of Bacillus sp. strains in combination with lactic acid bacteria for lignin degradation and enhancing cellulase performance was studied.
Generally, biological pretreatment rates are too slow for industrial purposes. However, Bacillus sp. CS-1 and CS-2 possessed high lignolytic enzyme activities (laccase activities) and lignin degradation time was very fast. The pretreated substrate (rice straw) was found to have greatly increased cellulase performance in accordance with decreased amounts of lignin and hemicellulose using the two-step pretreatment procedure with CS-1 and lactic acid bacteria. These results suggest that the two-step pretreatment procedure is effective at accelerating cellulase performance.
To the best of our knowledge, this is the first study reporting on lactic acid bacteria resulting in the reduction of hemicellulose, which leads to enhanced cellulase performance. As such, and along with the other findings of this study, we believe that this finding will be of interest to the readers of REGI.
The below Figure indicate that a schematic for the conversion of biomass to fuel and a conceptual scheme of biological pretreatment methods for the enhancing of cellulase performance.