Dokument: Discovery and Characterization of Fungal Secondary Metabolites with Antibacterial and Antibiofilm Activities
| Titel: | Discovery and Characterization of Fungal Secondary Metabolites with Antibacterial and Antibiofilm Activities | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=74817 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20261102-122512-7 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | He, Di [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Kalscheuer, Rainer [Gutachter] Prof. Dr. Frunzke, Julia [Gutachter] | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 570 Biowissenschaften; Biologie | |||||||
| Beschreibung: | Antimicrobial resistance and biofilm-associated infections severely limit the effectiveness of conventional anti-infective therapy, creating an urgent need to discover anti-infective lead compounds with new structures and novel modes of action. Fungal secondary metabolites possess rich structural diversity and broad biological activities and represent an important source of antibacterial and antibiofilm natural products. This dissertation mainly focuses on two projects concerning fungus-derived anti-infective natural products: first, the antibacterial activity of pestalotic acid A (PAA) derived from Pestalotiopsis chamaeropis against vancomycin-intermediate Staphylococcus aureus (VISA) and its mechanism of action; and second, the mature biofilm-disrupting activity and possible biosynthetic pathway of fusapurpurins A and B induced by co-cultivation of Fusarium oxysporum with Paenibacillus ehimensis.
The first part of this dissertation investigated the secondary metabolism of P. chamaeropis induced by the OSMAC strategy, leading to the isolation of a series of pestalotic acid-related natural products, including pestalotic acids A–H and pestaloside A. Among them, pestalotic acid H and pestaloside A were identified as new natural products, and the absolute configuration of pestalotic acid C was determined by single-crystal X-ray diffraction. Bioactivity evaluation showed that pestalotic acid A exhibited strong inhibitory activity against VISA, together with low cytotoxicity and low hemolytic activity. Mechanistic studies indicated that the activity of PAA against VISA was closely associated with cell envelope homeostasis. PAA mutants with reduced susceptibility obtained by continuous liquid-pressure selection all carried disruptive mutations in graR and showed increased susceptibility to vancomycin, daptomycin, polymyxin B, and colistin. Antibiotic synergy assays, cytochrome c binding assays, RT-qPCR, and proteomic results collectively suggested that PAA may interfere with GraRS-related cell envelope regulation, cell surface charge modification, and cell envelope stress adaptation. The action of PAA showed concentration-dependent characteristics: at low concentrations, it tended to interfere with the VISA-specific cell envelope adaptive state, whereas at high concentrations, it produced broader membrane-related or cell envelope-damaging effects. In addition, proteomic results showed that PAA downregulated proteins related to biofilm matrix synthesis, and experimental validation demonstrated that PAA inhibited VISA biofilm formation at sub-MIC concentrations, indicating that its anti-infective potential is reflected not only in the inhibition of planktonic cell growth, but also in the weakening of early biofilm establishment. The second part of this dissertation used a co-cultivation strategy to activate cryptic metabolic pathways in F. oxysporum, leading to the isolation of new compounds such as fusachinon, fusapurpurin A, and fusapurpurin B. Among them, fusapurpurins A and B are structurally unique bridged fusarubin derivatives and were confirmed by single-crystal X-ray diffraction to be racemates. Bioactivity studies showed that fusapurpurins A and B exhibited obvious disruptive effects on mature biofilms of S. aureus Mu50 and Pseudomonas aeruginosa PAO1, whereas their direct antibacterial activity was relatively weak. This suggests that their main value lies in interfering with mature biofilms rather than acting as conventional bactericidal agents. This result complements the biofilm formation-inhibitory activity of PAA, indicating that fungal natural products can act at different stages of the biofilm life cycle. To investigate the biosynthetic mechanism of fusapurpurins, this study combined genome sequencing, antiSMASH analysis, AlphaFold structure prediction, US-align structural comparison, and Chai-1 protein–ligand complex prediction, and proposed that the FO-LovD-like protein may participate in the coupling reaction between 9-O-methylfusarubin and an activated phenylpyruvate-derived acyl donor. According to the current model, subsequent oxidative dehydrogenation may generate a reactive intermediate, which may further undergo non-stereoselective Diels–Alder-like cyclization to form fusapurpurins A and B. The fact that both products are racemates supports the possibility that the final cyclization process lacks clear chiral control. Since phenylpyruvic acid or defined reaction intermediates could not be detected in the extracts, this biosynthetic hypothesis still requires further validation through in vitro enzymatic reactions, substrate feeding, targeted LC-MS/MS, and genetic experiments. In addition, this dissertation also includes the determination of the sugar configuration in glycosylated asperphenalenone derivatives derived from Clonostachys rosea. In summary, this dissertation demonstrates the multiple values of fungal secondary metabolites in research on drug-resistant bacteria, antibiofilm activity, and natural product biosynthesis. PAA revealed a potential vulnerability in the cell envelope adaptive state of VISA, while fusapurpurins A and B demonstrated the application potential of co-culture-induced metabolites in disrupting mature biofilms. These results provide an important basis for the discovery of new anti-infective natural product lead structures, the exploration of antibiofilm strategies, and the understanding of late-stage biosynthetic processes in fungal natural products. | |||||||
| Lizenz: |  Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung 4.0 International Lizenz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Pharmazie » Pharmazeutische Biologie und Biotechnologie | |||||||
| Dokument erstellt am: | 02.11.2026 | |||||||
| Dateien geändert am: | 02.11.2026 | |||||||
| Promotionsantrag am: | 12.08.2026 | |||||||
| Datum der Promotion: | 26.10.2026 |
