AUTHOR=Su Qixuan , Cheng Ping , Sun Jiyuan , Zhang Yulin , Zheng Yang , Jiang Xiao-Ran , Rao Xiancai 

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

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1100745

DOI=10.3389/fmicb.2022.1100745

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p>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. <italic>Halomonas bluephagenesis</italic> is a versatile chassis for the production of fine chemicals because of its open growth property without sterilization.</p></sec><sec><title>Methods</title><p>A heterologous mevalonate (MVA) pathway was introduced into <italic>H. bluephagenesis</italic> 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 <italic>P<sub>Mmp1</sub></italic> and an <italic>Escherichia coli P<sub>trc</sub></italic> promoters and a pTer3 plasmid providing lycopene biosynthesis downstream genes derived from <italic>Streptomyces avermitilis</italic> were constructed and transformed into TD1.0. The production of lycopene in the engineered <italic>H. bluephagenesis</italic> was evaluated. Optimization of engineered bacteria was performed to increase lycopene yield.</p></sec><sec><title>Results</title><p>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 <italic>S. lividans</italic> elevated the lycopene production to 0.70 mg/g DCW in the TD1.0/pTer7-pTer5 strain. Optimizing the <italic>P<sub>Mmp1</sub></italic> promoter in plasmid pTer7 with a relatively weak <italic>P<sub>trc</sub></italic> even increased the lycopene production to 1.22 mg/g DCW. However, the change in the <italic>P<sub>trc</sub></italic> promoter in pTer7 with <italic>P<sub>Mmp1</sub></italic> did not improve the yield of lycopene.</p></sec><sec><title>Conclusion</title><p>We first engineered an <italic>H. bluephagenesis</italic> 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.</p></sec>