Engineering a mevalonate pathway in Halomonas bluephagenesis for the production of lycopene

Abstract

Introduction: Red-colored lycopene has received remarkable attention in medicine because of its antioxidant properties for reducing the risks of many human cancers. However, the extraction of lycopene from natural hosts is limited. Moreover, the chemically synthesized lycopene raises safety concerns due to residual chemical reagents. Halomonas bluephagenesis is a versatile chassis for the production of fine chemicals because of its open growth property without sterilization.

Methods: A heterologous mevalonate (MVA) pathway was introduced into H. bluephagenesis strain TD1.0 to engineer a bacterial host for lycopene production. A pTer7 plasmid mediating the expression of six MVA pathway genes under the control of a phage P_Mmp1 and an Escherichia coli P_trc promoters and a pTer3 plasmid providing lycopene biosynthesis downstream genes derived from Streptomyces avermitilis were constructed and transformed into TD1.0. The production of lycopene in the engineered H. bluephagenesis was evaluated. Optimization of engineered bacteria was performed to increase lycopene yield.

Results: The engineered TD1.0/pTer7-pTer3 produced lycopene at a maximum yield of 0.20 mg/g dried cell weight (DCW). Replacing downstream genes with those from S. lividans elevated the lycopene production to 0.70 mg/g DCW in the TD1.0/pTer7-pTer5 strain. Optimizing the P_Mmp1 promoter in plasmid pTer7 with a relatively weak P_trc even increased the lycopene production to 1.22 mg/g DCW. However, the change in the P_trc promoter in pTer7 with P_Mmp1 did not improve the yield of lycopene.

Conclusion: We first engineered an H. bluephagenesis for the lycopene production. The co-optimization of downstream genes and promoters governing MVA pathway gene expressions can synergistically enhance the microbial overproduction of lycopene.

Keywords: Halomonas bluephagenesis; carotenoid products; lycopene; lycopene biosynthesis; mevalonate pathway.