Engineering of
Ruizhao Wang,Xiaoli Gu,Mingdong Yao,Caihui Pan,Hong Liu,Wenhai Xiao,Ying Wang,Yingjin Yuan
《化学科学与工程前沿（英文）》
2017年
第11卷
第1期
页码 89-99
doi:
10.1007/s11705-017-1628-0
摘要：
The conversion of -carotene to astaxanthin is a complex pathway network, in which two steps of hydroxylation and two steps of ketolation are catalyzed by -carotene hydroxylase (CrtZ) and -carotene ketolase (CrtW) respectively. Here, astaxanthin biosynthesis pathway was constructed in by introducing heterologous CrtZ and CrtW into an existing high -carotene producing strain. Both genes and were codon optimized and expressed under the control of constitutive promoters. Through combinatorial expression of CrtZ and CrtW from diverse species, nine strains in dark red were visually chosen from thirty combinations. In all the selected strains, strain SyBE_Sc118060 with CrtW from DC263 and CrtZ from sp. strain PC-1 achieved the highest astaxanthin yield of 3.1 mg/g DCW. Protein phylogenetic analysis shows that the shorter evolutionary distance of CrtW is, the higher astaxanthin titer is. Further, when the promoter of in strain SyBE_Sc118060 was replaced from FBA1p to TEF1p, the astaxanthin yield was increased by 30.4% (from 3.4 to 4.5 mg/g DCW). In the meanwhile, 33.5-fold increase on transcription level and 39.1-fold enhancement on the transcriptional ratio of to were observed at early exponential phase in medium with 4% (w/v) glucose. Otherwise, although the ratio of to were increased at mid-, late-exponential phases in medium with 2% (w/v) glucose, the transcription level of both and were actually decreased during the whole time course, consequently leading to no significant improvement on astaxanthin production. Finally, through high cell density fed-batch fermentation using a carbon source restriction strategy, the production of astaxanthin in a 5-L bioreactor reached to 81.0 mg/L, which was the highest astaxanthin titer reported in yeast. This study provides a reference to greatly enhance desired compounds accumulation by employing the key enzyme(s) in microbes.
关键词：
synthetic biology
astaxanthin
β-carotene hydroxylase
β-carotene ketolase
Saccharomyces cerevisiae
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