Dynamic changes of endophytic bacteria in the bark and leaves of medicinal plant Eucommia ulmoides in different seasons.

The bark and leaves of the Eucommia ulmoides Oliv. (E. ulmoides) have good medicinal value. Studies show endophytes play important roles in host medicinal plant secondary metabolite synthesis, with season being a key influencing factor. Therefore, we used 16 S rRNA to detect endophytic bacteria (EB) in E. ulmoides bark and leaves collected in winter, spring, summer, and autumn, and analyzed the contents of major active components respectively. The results showed that the species diversity and richness of EB of the E. ulmoides bark were higher than those of leaves in all seasons except fall. Among them, the higher species diversity and richness were found in the E. ulmoides bark in winter and spring. EB community structure differed significantly between medicinal tissues and seasons. Concurrently, the bark and leaves of E. ulmoides showed abundant characteristic EB across seasons. For active components, geniposidic acid showed a significant positive correlation with EB diversity and richness, while the opposite was true for aucubin. Additionally, some dominant EB exhibited close correlations with the accumulation of active components. Delftia, enriched in autumn, correlated significantly positively with aucubin. Notably, the impact of the same EB genera on active components differed across medicinal tissues. For example, Sphingomonas, enriched in summer, correlated significantly positively with pinoresinol diglucoside (PDG) in the bark, but with aucubin in the leaves. In summary, EB of E. ulmoides was demonstrated high seasonal dynamics and tissue specificity, with seasonal characteristic EB like Delftia and Sphingomonas correlating with the accumulation of active components in medicinal tissues.