ABSTRACT
Zearalenone (ZEN) and its derivatives are non-steroidal estrogenic mycotoxins mainly produced by Fusarium species. They are widely distributed in grain feeds originated from maize, barley, wheat and sorghum, causing serious harm to animal and human health. Currently, there is a pressing need of an efficient technology for ZEN degradation and detoxification. Because traditional physical and chemical methods could not effectively detoxify ZEN in grains, and might also affect the grain nutrients and food taste, and even result in secondary pollution, the biological technologies are developed to detoxify ZEN and its derivatives. In this paper, we reviewed the structure of ZEN and its derivatives, the fungi and bacteria species with ability of degradation of ZEN. In addition, the characterization, protein sequences and conformation of currently identified ZEN degrading enzymes, the only solved ZHD structure from Clonostachys rose were analyzed and compared, and the enzymes heterologous expression and application were also reviewed. This review will provide reference for reducing the cost of ZEN degrading enzymes by biological technologies such as enzyme engineering and fermentation engineering.
ABSTRACT
Pectate lyase is widely applied in ramie degumming and fabric bioscouring in the textile industry. Compared to conventional processes that involve high alkaline and high temperature treatment, enzyme based treatments have significant advantages in fibers protectiveness, improved efficiency of refining, reduced energy consumption and pollution. Hence, it would be highly desirable to construct high-yield alkaline pectate lyase engineered strains and reduce the pectate lyase production cost. In the previous study, pectate lyase gene pel from Bacillus subtilis168 was expressed in Pichia pastoris GS115 after codon usage optimization based on the vector pHBM905A. To improve the expression level, the vector pHBM905BDM with optimized promoter and signal peptide was used to express the optimized gene pels in GS115. The transformant had increased activity from 68 U/mL to 100 U/mL with the improvement in the transcription level by 27% measured by qPCR. The transformants were further screened on pectin plates, where higher halo forming strains were picked for shake-flask fermentation and strain GS115-pHBM905BDM-pels4 showed the highest activity of 536 U/mL. Then plasmid pPIC9K-pels was constructed and electroporated into the GS115-pHBM905BDM-pels4 cells. Subsequently, high-copy transformant was screened by using the medium containing antibiotics G418, strain GS115-pHBM905BDMpPIC9K- pels1 was identified with increased activity of 770 U/mL and the copy number of pels was 7 confirmed by qPCR. Finally, the activity of pectate lyase produced by GS115-pHBM905BDM-pPIC9K-pels1reached to 2 271 U/mL in a 5-L fermentor. The activity of pectate lyase in our study reached the highest level of expression in P. pastoris, showing good application potential in the textile industry.