Abstract
BackgroundThe dried roots and rhizomes of medicinal licorices are widely used worldwide as a traditional medicinal herb, which are mainly attributed to a variety of bioactive compounds that can be extracted from licorice root. Endophytes and plants form a symbiotic relationship, which is an important source of host secondary metabolites.ResultsIn this study, we used high-throughput sequencing technology and high-performance liquid chromatography to explore the composition and structure of the endophytic bacterial community and the content of bioactive compounds (glycyrrhizic acid, liquiritin and total flavonoids) in different species of medicinal licorices (Glycyrrhiza uralensis, Glycyrrhiza glabra, and Glycyrrhiza inflata) and in different planting years (1–3 years). Our results showed that the contents of the bioactive compounds in the roots of medicinal licorices were not affected by the species, but were significantly affected by the main effect growing year (1–3) (P < 0.05), and with a trend of stable increase in the contents observed with each growing year. In 27 samples, a total of 1,979,531 effective sequences were obtained after quality control, and 2432 effective operational taxonomic units (OTUs) were obtained at 97% identity. The phylum Proteobacteria, Actinobacteria, Bacteroidetes and Firmicutes, and the genera unified-Rhizobiaceae, Pseudomonas, Novosphingobium, and Pantoea were significantly dominant in the 27 samples. Distance-based redundancy analysis (db-RDA) showed that the content of total flavonoids explained the differences in composition and distribution of endophytic bacterial communities in roots of cultivated medicinal liquorices to the greatest extent. Total soil salt was the most important factor that significantly affected the endophytic bacterial community in soil factors, followed by ammonium nitrogen and nitrate nitrogen. Among the leaf nutrition factors, leaf water content had the most significant effect on the endophytic bacterial community, followed by total phosphorus and total potassium.ConclusionsThis study not only provides information on the composition and distribution of endophytic bacteria in the roots of medicinal licorices, but also reveals the influence of abiotic factors on the community of endophytic bacteria and bioactive compounds, which provides a reference for improving the quality of licorice.
Highlights
The dried roots and rhizomes of medicinal licorices are widely used worldwide as a traditional medicinal herb, which are mainly attributed to a variety of bioactive compounds that can be extracted from licorice root
The effect of the growing year on the content of bioactive compounds in the roots of medicinal licorices The results of two-way Analysis of variance (ANOVA) showed that the contents of the bioactive compounds (glycyrrhizic acid (GIA), liquiritin (LI) and total flavonoid (GTF)) were not significantly affected by the interaction effect between growing year (1–3) and plant species (Glycyrrhiza uralensis, Glycyrrhiza inflata, and Glycyrrhiza glabra) (P > 0.05) (Table 1)
The contents of the bioactive compounds were significantly affected by the main effect growing year (1–3) (P < 0.05) (Table 1 and Fig. 1), with a trend of stable increase in the contents observed with each growing year
Summary
The dried roots and rhizomes of medicinal licorices are widely used worldwide as a traditional medicinal herb, which are mainly attributed to a variety of bioactive compounds that can be extracted from licorice root. The term endophyte describes those taxa that can live within plant tissues, either within or between host cells [1]. These endophytes include bacteria, fungi, archaea and unicellular eukaryotes [2]. As biological control agents, endophytic bacteria can produce or promote the production of secondary metabolites by host plants to reduce or prevent damage caused by certain pathogens [10, 11]. Numerous studies have shown that an in-depth understanding of the diversity of endophytic bacteria will elucidate the function of the interaction between microorganisms and plants, which will be conducive to the development of strategies for ecological environment restoration and sustainable agricultural, such as remediation of the soil environment [12] and increasing crop production [13]
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