Heterologous expression of Xanthophyllomyces dendrorhous crtS/crtR in Escherichia coli for preliminary astaxanthin formation.

Astaxanthin biosynthesis in engineered bacteria commonly relies on CrtW/CrtZ enzymes, whereas functional reconstruction of the yeast P450-type CrtS/CrtR module in Escherichia coli remains less established. Here, crtS and crtR from Xanthophyllomyces dendrorhous were introduced into pBR322-derived vectors and co-expressed with pAC-BETAipi in E. coli DH5α. The parental pAC-BETAipi strain and the CrtS/CrtR co-expression strain showed comparable growth profiles. HPLC analysis of the co-expression strain revealed an astaxanthin-associated target peak at 2.734 min. After addition of the astaxanthin standard to the same extract, the target-peak area increased from 448,930 to 812,037 while the retention time remained essentially unchanged (2.734 versus 2.732 min). Among five carbon sources, maltose gave the highest wet-biomass-normalized target-peak yield (16.28 ± 0.29 μg/g; P < 0.05). Under a nominal C/N ratio of 6:1, product selectivity reached 73.8%. These results support functional compatibility of the yeast CrtS/CrtR module with a bacterial β-carotene background and identify culture conditions favoring the astaxanthin-associated target peak.