A Potential Strategy for Improving Ginseng Growth and Ginsenoside Biosynthesis: Application of a PQQ-Producing Ginseng Endophyte

Panax ginseng C.A. Meyer is a valuable medicinal plant with considerable pharmaceutical and economic importance. However, long-term cultivation of ginseng faces several challenges, including replanting problems, yield decline, and unstable quality, which severely restrict the sustainable development of the ginseng industry. Plant endophytes are microorganisms that establish long-term associations with their hosts, and their bioactive metabolites have great potential for promoting host growth, enhancing stress tolerance, and modulating secondary metabolism. In this study, a total of 134 ginseng endophytes were isolated from 15 forest-grown ginseng samples. Among them, the pyrroloquinoline quinone (PQQ)-producing strain W7N-70 (PQQ yield: 41.99 mg/L), belonging to the genus Methylorubrum, was screened. The engineered strain W7N-70-PqqABCDE (PQQ yield: 92.55 mg/L) was constructed through overexpression of the PQQ biosynthetic gene cluster, and fermentation conditions were optimized using response surface methodology, resulting in a significantly enhanced PQQ yield of 149.29 mg/L. Furthermore, ginseng adventitious roots were treated with culture supernatants from strain W7N-70 and the engineered strain W7N-70-PqqABCDE, as well as exogenous PQQ. The results showed that the culture supernatant of the engineered strain significantly promoted adventitious root growth, increased indole-3-acetic acid (IAA) content, and enhanced antioxidant enzyme activities. Moreover, it significantly upregulated the expression of key enzyme genes involved in the protopanaxadiol (PPD)-type ginsenoside biosynthetic pathway and significantly increased the content of PPD-type ginsenosides. Overall, this study provides novel microbial resources for PQQ biosynthesis and preliminarily demonstrates the potential of PQQ-producing strains to promote ginseng growth, modulate physiological responses, and improve ginsenoside production.