Metabolic Profiling of Water-Soluble Compounds from the Extracts of Dark Septate Endophytic Fungi (DSE) Isolated from Scots Pine (Pinus sylvestris L.) Seedlings Using UPLC–Orbitrap–MS

Abstract

Endophytes are microorganisms living inside plant hosts and are known to be beneficial for the host plant vitality. In this study, we isolated three endophytic fungus species from the roots of Scots pine seedlings growing on Finnish drained peatland setting. The isolated fungi belonged to dark septate endophytes (DSE). The metabolic profiles of the hot water extracts of the fungi were investigated using Ultrahigh Performance Liquid Chromatography with Diode Array Detection and Electron Spray Ionization source Mass Spectrometry with Orbitrap analyzer (UPLC–DAD–ESI–MS–Orbitrap). Out of 318 metabolites, we were able to identify 220, of which a majority was amino acids and peptides. Additionally, opine amino acids, amino acid quinones, Amadori compounds, cholines, nucleobases, nucleosides, nucleotides, siderophores, sugars, sugar alcohols and disaccharides were found, as well as other previously reported metabolites from plants or endophytes. Some differences of the metabolic profiles, regarding the amount and identity of the found metabolites, were observed even though the fungi were isolated from the same host. Many of the discovered metabolites have been described possessing biological activities and properties, which may make a favorable contribution to the host plant nutrient availability or abiotic and biotic stress tolerance.

Bioactive Properties of the Aqueous Extracts of Endophytic Fungi Associated with Scots Pine (Pinus sylvestris) Roots

“…Other compounds such as nucleosides and nucleotides, Amadori compounds, and sugars were also found among the compounds of potential bioactive interest, representing 19 % of the metabolites. As found in our previous study [6], the fungal species have surprisingly similar metabolomes. A and R fungi belong to the Phialocephala fortinii-Acephala applanata complex (PAC), which are usually common root endophytes in the boreal trees, whereas S16 is Humicolopsis cephalosporioides or Coniochaeta mutabilis, which have been found in plants but also act as human and animal pathogens.…”

“…The data obtained was then connected with the information about the metabolites putatively annotated. The metabolic profile of the fungal extracts A. applanata (cultivation code A), P. fortinii (R), and H. cephalosporioides or C. mutabilis (S16) was described in an earlier study [6]. For simplicity, the cultivation codes A, R, and S16 of the extracts are used.…”

“…The metabolic profiling process and all the putatively annotated and unidentified metabolites from the fungal extracts have been described earlier [6]. The information about the characterization of the metabolites by high-resolution mass spectrometry containing, for example, the structural information with measured exact masses and in-source fragment ions, retention times, and the standards used, are also shown in Tienaho et al [6]. All metabolites discovered from the extracts and fractions are shown in Table 1S, Supporting Information, while ▶ Table 2 shows the metabolites that have been only found in the active or only in the inactive fractions and extracts.…”

“…We have previously described the metabolites in the aqueous extracts of three DSE fungi, Acephala applanata (Leotimycetidae), Phialocephala fortinii (Leotimycetidae), and Humicolopsis cephalosporioides (Sordariomycetidae)/Coniochaeta mutabilis (Sordariomycetidae) (The collection of Natural Resources Institute Finland) isolated from the Scots pine roots growing on drained peatlands. Out of 318 metabolites from 3 fungus extracts, 220 were putatively annotated [6]. While there are numerous studies focusing on the endophytic fungi extraction with organic solvents, little is known about the water-extractable metabolites obtained from endophytic fungi and their bioactivities.…”

“…Finally, the bioactive properties of the active or inactive fractions of the extracts were examined together with the data of the metabolite composition of the fractions. These were obtained in our earlier study [6] using high-resolution LC-MS.…”