Fungal Secondary Metabolites: Fusarium spp. and Microdochium spp.
by Albatol Alsarrag
Date of Examination:2021-07-16
Date of issue:2022-12-06
Advisor:Prof. Dr. Petr Karlovsky
Referee:PD Dr. Franz Hadacek
Referee:Prof. Dr. Michael Rostás
Files in this item
Name:Doctoral thesis-Albatol Alsarrag.pdf
EnglishThe key characteristic of aurofusarin is the repellent effect against fungivores. We confirmed the previous finding that the red pigment aurofusarin is a water-insoluble metabolite, and it is preferably soluble in non-polar solvents. Aurofusarin dissolved readily in m-cresol and chloroform/methanol. The last solvent mixture is preferable to extract aurofusarin from the fungal mycelium. During the chemical analysis, aurofusarin was protected from degradation by dissolving it in a water-free solvent. Some studies revealed that the biosynthesis of fungal secondary metabolites is dependent on ambient conditions. Here we demonstrated the inhibition effect of the commercial PDB medium on the accumulation of aurofusarin. Simultaneously aurofusarin was produced generously on freshly prepared PDB. Moreover, the molar extinction coefficient of aurofusarin was determined to be 21,600 M−1cm−1 at λmax of 266 nm. On the other hand, the toxicity of M. nivale and M. majus against mealworms, springtails, brine shrimps, radish seeds, and duckweeds was investigated. All M. majus strains displayed a non-toxic effect, whereas some strains in M. nivale strains were toxic to the tested organisms; among them, one strain reduced the fitness of the organisms in all bioassays. Consequently, two bioactive compounds (phytotoxic and cytotoxic) were isolated from this strain. The phytotoxic compound has been determined to bestreptol ((1S,2S,3S,4R)-5-(hydroxymethyl)cyclohex-5-ene-1,2,3,4-tetrol). This compound is known as a bacterial secondary metabolite possessing a phytotoxic effect. However, this is the first time to report this compound in fungi.
Keywords: Biosynthesis pathway; Bis-naphthopyrone; Phytotoxic