Influence of culture conditions on the antifungal performance of an Antarctic fungus (Cadophora malorum)

MARTORELL MM; FASCETTO G ; DONALLE, GUIDMAR C.; PERALTA P; CABRERA G; MAC CORMACK WP; RUBERTO L

Mendoza

Encuentro; LVIII Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology Research; 2022

SAIB

The ability of fungi to produce molecules with biological activity is confirmed by studying the growing number of fungal sequenced genomes, which showed that their metabolic potential has been vaguely explored. These sequences also showed that many of the fungal genes involved in secondary metabolites synthesis are clustered, being the expression of many of them silent under standard culture conditions. In that way, stress, or changes in growth conditions, can result in a significantly different physiological behavior, with consequent differential metabolite production.Filamentous fungi from regions with extreme conditions present physiological adaptations that result in metabolic pathways able for producing novel molecules with antimicrobial activity encoded in gene clusters that are silent and whose expression can be triggered by exposure to physicochemical, mechanical, or biological stress. In this work, the effect of a different kind of stress on the secondary metabolites production profile of a strain of the Antarctic fungi Cadophora malorum was evaluated. The fungus was cultivated in potato dextrose medium (PD) in solid (PDA), liquid (PDB), and inert solid (Polyuretane foam) under different temperatures (5, 10, and 15°C) and agitation conditions (static and 200 rpm). Additionally, the effect of mechanical damage to the mycelia was evaluated. After 28 days of culture, the biomass-free culture supernatant was extracted with ethyl acetate; the organic phase was evaporated and resuspended in methanol to evaluate their antifungal activity against a set of filamentous fungi and yeasts of clinical relevance using the Kirby-Bauer technique. Also, RP-HPLC analysis of the extracts was done to compare metabolite profiles. Different levels of antifungal activity, expressed as inhibition diameter (ID, cm), were observed. The highest inhibition was obtained from cultures growing under static conditions in liquid media at 15°C, showing activity (ID) against Candida albicans (2,23±0.08), C. haemulonii (1.03±0.08), Aspergillus fumigatus (1,32±0.09), and A. lentulus (1,11±0.12). As a control, 20 μl of Cycloheximide (10 mg/ml) was used showing the following ID (1.08±0,04, 1.98±0,11, 2.95±0.70, 3.1±0.5 respectively). Mechanical damage to the mycelia did not change the antifungal performance of C. malorum. When the HPLC profiles were analyzed, several changes in the variety and size of peaks were observed. Rhizopus sp showed no inhibition when challenged with extracts obtained from all the tested conditions.These results highlighted the relevance of exploring fungal culture and environmental conditions when looking for bioactivity. The procedure present in this summary is going to be applied to continue exploring the metabolic diversity of Antarctic fungi.