Study of a High-Yield Cellulase System Created by Heavy-Ion Irradiation-Induced Mutagenesis of Aspergillus niger and Mixed Fermentation with Trichoderma reesei.

Shu-Yang Wang,Yu-Chen Wang,Guo-Qing Xiao,Ji-Hong Chen,Jing Liu,Bo-Ling Jiang,Wei Hu,Wen-Jian Li,Miao-Yin Dong,Xiang Zhou,Shihui Yang

doi:10.1371/journal.pone.0144233

Abstract

The aim of this study was to evaluate and validate the efficiency of 12C6+ irradiation of Aspergillus niger (A. niger) or mutagenesis via mixed Trichoderma viride (T. viride) culturing as well as a liquid cultivation method for cellulase production via mixed Trichoderma reesei (T. reesei) and A. niger culture fermentation. The first mutagenesis approach was employed to optimize yield from a cellulase-producing strain via heavy-ion mutagenesis and high-throughput screening, and the second was to effectively achieve enzymatic hydrolysis of cellulase from a mixed culture of mutant T. viride and A. niger. We found that 12C6+-ion irradiation induced changes in cellulase biosynthesis in A. niger but had no effect on the time course of the synthesis. It is notable that the exoglucanases (CBH) activities of A. niger strains H11-1 and H differed (6.71 U/mL vs. 6.01 U/mL) and were significantly higher than that of A. niger mutant H3-1. Compared with strain H, the filter paper assay (FPA), endoglucanase (EG) and β-glucosidase (BGL) activities of mutant strain H11-1 were increased by 250.26%, 30.26% and 34.91%, respectively. A mixed culture system was successfully optimized, and the best ratio of T. reesei to A. niger was 5:1 for 96 h with simultaneous inoculation. The BGL activity of the mixed culture increased after 72 h. At 96 h, the FPA and BGL activities of the mixed culture were 689.00 and 797.15 U/mL, respectively, significantly higher than those of monocultures, which were 408.70 and 646.98 U/mL for T. reesei and 447.29 and 658.89 U/mL for A. niger, respectively. The EG activity of the mixed culture was 2342.81 U/mL, a value that was significantly higher than that of monocultures at 2206.57 U/mL for T. reesei and 1727.62 U/mL for A. niger. In summary, cellulose production and hydrolysis yields were significantly enhanced by the proposed combination scheme.

Highlights

There is increasing interest in sustainable methods to meet the growing energy demands of transportation, heating and industrial processes and in providing raw materials for industry [1]
Survival data for the A. niger colonies is shown in Fig 1A as a plot of survival against irradiation dose; 12C6+ heavy-ion irradiation for 20, 40, 60, 80, 100 and 120 Gy resulted in 90.7%, 14.5%, 68.3%, 55.3%, 36.5% and 13.8% survival rates, respectively
A. niger was screened for a high EG substrate affinity, and EGs and BGLs were obtained in strains with higher mutation rates

Summary

Introduction

There is increasing interest in sustainable methods to meet the growing energy demands of transportation, heating and industrial processes and in providing raw materials for industry [1]. As the use of food as a raw material for biological and industrial fuels has caused global concerns of food safety and significantly affected the public acceptance of biofuels, biofuel research is focusing on the development of next-generation biofuels. To this end, the synthesis of bioethanol from lignocellulosic raw materials, e.g., agricultural and forestry residues, portions of municipal waste, and herbaceous and woody crops, is a promising option for nonfood biofuel production [2,3]. Cellulases are still comparatively costly, and the need to reduce production costs is of great importance for their industrial and commercial use in biorefineries [7]

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Conclusion