Production of astaxanthin with high purity and activity based on engineering improvement strategies

Here, astaxanthin production in Escherichia coli was systematically improved step by step. By introducing the additional copy of CrtZ and fusion complex of CrtZ and CrtW, astaxanthin content in cells increased from 0.10 mg/g to 0.16 mg/g and 0.63 mg/g DCW, respectively. Remolding the astaxanthin gene cluster by replacing the PanCrtE by HpGGPPS3-1 and the fusion of CrtZ and CrtW increased astaxanthin content to 1.98 mg/g DCW. Further selecting the productive host and optimizing culture conditions dramatically increased astaxanthin content to 3.61 mg/g DCW. Subsequently, the fed-batch fermentation achieved the maximum yield of astaxanthin at 509.58 mg/L with the productivity of 7.72 mg/L/h and 5.91 mg/g DCW, covering 98.17 % of detected carotenoids. The chirality analysis assigned the same isomer of astaxanthin extracted from our fermentation system and Haematococcus pluvialis. Moreover, the radical and superoxide anion scavenging activity analysis revealed that astaxanthin achieved in this study performed better than natural astaxanthin extracted from H. pluvialis and chemical synthetic astaxanthin. This study provides a step-by-step example for bioengineering improvement of natural products in E. coli with high purity and activity.