Various Achillea species are rich in bioactive compounds and are important medicinal plants in phytotherapy. In the present study, Achillea millefolium L., Achillea moschata Wulfen, and Achillea atrata L. were compared with respect to their phenolic profile and antibacterial activity against gram-positive bacteria strains (Staphylococcus, Propionibacterium). Particular focus was given to A. atrata, which has hardly been studied so far. Based on the metabolite profile, A. atrata exhibited more similarities to A. moschata than to A. millefolium. The former two only differed in the occurrence of four compounds. The flavonols syringetin-3-O-glucoside and mearnsetin-hexoside, not reported for an Achillea species before, have been detected in A. atrata and A. moschata. All Achillea species reduced growth of the tested bacteria. A. atrata demonstrated highest activity against Propionibacterium acnes and Staphylococcus epidermidis, both being involved in the pathogenesis of acne vulgaris. Furthermore, A. atrata has a pronounced anti–methicillin-resistant Staphylococcus aureus potential. Bioassay-guided fractionation revealed that only the most polar fraction of A. moschata displayed antimicrobial activity, which was attributed to phenolics such as apigenin, centaureidin, and nevadensin, being present in high amounts in A. atrata. Thus, this alpine species shows promising antimicrobial activity and might be a potential source for developing novel dermal/topical drugs.
In the recent past many studies investigated the microbiome of plants including several medicinal plants (MP). Microbial communities of the associated soil, rhizosphere and the above-ground organs were included, but there is still limited information on their seasonal development, and in particular simultaneous investigations of different plant organs are lacking. Many studies predominantly addressed either the prokaryotic or fungal microbiome. A distinction of epi- and endophytic communities of above-ground plant organs has rarely been made. Therefore, we conducted a comprehensive investigation of the bacterial and fungal microbiome of the MP Achillea millefolium and studied the epi- and endophytic microbial communities of leaves, flower buds and flowers between spring and summer together with the microbiome of the associated soil at one location. Further, we assessed the core microbiome of Achillea from four different locations at distances up to 250 km in southern Germany and Switzerland. In addition, the bacterial and fungal epi- and endophytic leaf microbiome of the arborescent shrub Hamamelis virginiana and the associated soil was investigated at one location. The results show a generally decreasing diversity of both microbial communities from soil to flower of Achillea. The diversity of the bacterial and fungal endophytic leaf communities of Achillea increased from April to July, whereas that of the epiphytic leaf communities decreased. In contrast, the diversity of the fungal communities of both leaf compartments and that of epiphytic bacteria of Hamamelis increased over time indicating plant-specific differences in the temporal development of microbial communities. Both MPs exhibited distinct microbial communities with plant-specific but also common taxa. The core taxa of Achillea constituted a lower fraction of the total number of taxa than of the total abundance of taxa. The results of our study provide a basis to link interactions of the microbiome with their host plant in relation to the production of bioactive compounds.
Microbial fermentation of plant extracts with Lactobacteria is an option to obtain microbiologically stable preparations, which may be applied in complementary medicine. We investigated the metabolic conversion of constituents from Mercurialis perennis L. extracts, which were prepared for such applications. For this purpose, aqueous extracts were inoculated with two Lactobacteria strains, namely Pediococcus sp. (PP1) and Lactobacillus sp. (LP1). Both were isolated from a fermented M. perennis extract and identified by 16S rRNA sequencing. After 1 day of fermentation, an almost complete conversion of the genuine piperidine-2,6-dione alkaloids hermidine quinone (3) and chrysohermidin (4)—both of them being oxidation products of hermidin (1) —was observed by GC-MS analysis, while novel metabolites such as methylhermidin (6) and methylhermidin quinone (7) were formed. Surprisingly, a novel compound plicatanin B (bis-(3-methoxy-1N-methylmaleimide); 8) was detected after 6 days, obviously being formed by ring contraction of 4. An intermediate of a postulated reaction mechanism, isochrysohermidinic acid (14), could be detected by LC-MS. Furthermore, an increase in contents of the metabolite mequinol (4-methoxyphenol; 9) upon fermentation points to a precursor glycoside of 9, which could be subsequently detected by GC-MS after silylation and identified as methylarbutin (15). 15 is described here for M. perennis for the first time.
The fermentation of medicinal plants has been studied very little, as compared to the fermentation of food and beverages. One approach applies fermentation by single bacterial or fungal strains and targets the production of specific compounds or preservation of the fermented material. Spontaneous fermentation by an autochthonous starter community may lead to a more diverse blend of fermentation products because co-occurring microbes may activate the biosynthetic potentials and formation of compounds not produced in single strain approaches. We applied the community approach and studied the fermentation of four medicinal plants (Achillea millefolium, Taraxacum officinale, Mercurialis perennis, and Euphrasia officinalis), according to a standardized pharmaceutical fermentation method. It is based on the spontaneous fermentation by plant-specific bacterial and fungal communities under a distinct temperature regime, with a recurrent cooling during the first week and further fermentation for at least six months. The results revealed both general and plant-specific patterns in the composition and succession of microbial communities during fermentation. Lactic acid bacteria increasingly dominated in all preparations, whereas the fungal communities retained more plant-specific features. Three distinct fermentation phases with characteristic bacterial communities were identified, i.e., early, middle, and late phases. Co-occurrence network analyses revealed the plant-specific features of the microbial communities.
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