Comparative metabolomics study on the secondary metabolites of the red alga, <i>Corallina officinalis</i> and its associated endosymbiotic fungi

Abstract

Marine endosymbionts have gained remarkable interest in the last three decades in terms of natural products (NPs) isolated thereof, emphasizing the chemical correlations with those isolated from the host marine organism. The current study aimed to conduct comparative metabolic profiling of the marine red algae <i>Corallina officinalis</i>, and three fungal endosymbionts isolated from its inner tissues namely, <i>Aspergillus nidulans</i>, <i>A. flavipes</i> and <i>A. flavus</i>. The ethyl acetate (EtOAc) extracts of the host organism as well as the isolated endosymbionts were analyzed using ultra-high performance liquid chromatography coupled to high resolution tandem mass spectrometry (UHPLC-MS/MS)in both positive and negative ion modes, applying both full scan (FS) and all ion fragmentation (AIF) modes. Extensive interpretation of the LC-MS/MS spectra had led to the identification of 76 metabolites belonging to different phytochemical classes including alkaloids, polyketides, sesquiterpenes, butyrolactones, peptides, fatty acids, isocoumarins, quinones, among others. Metabolites were tentatively identified by comparing the accurate mass and fragmentation pattern with metabolites previously reported in the literature, as well as bioinformatics analysis using GNPS. A relationship between the host <i>C. officinalis</i> and its endophytes (<i>A. flavus</i>, <i>A. nidulans</i>, and <i>A. flavipes</i>) was discovered. <i>C. officinalis</i> shares common metabolites with at least one of the three endosymbiotic fungi. Some metabolites have been identified in endophytes and do not exist in their host. Multivariate analysis (MVA) revealed discrimination of <i>A. flavipes</i> from <i>Corallina officinalis</i> and other associated endophytic <i>Aspergillus</i> fungi (<i>A. flavus</i> and <i>A. nidulans</i>).