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

MARTORELL MM; FASCETTO CASSERO; PERALTA, M.P.; DONALLE, GUIDMAR; CABRERA, GABRIELA; MAC CORMACK, WALTER P.; RUBERTO LAM

Mendoza

Congreso; Congreso SAIB 2022; 2022

SAIB

The ability of fungi to produce molecules with biological activity is confirmed by studying the growingnumber of fungal sequenced genomes, which showed that their metabolic potential has been vaguelyexplored. These sequences also showed that many of the fungal genes involved in secondary metabolitessynthesis 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 physiologicalbehavior, with consequent differential metabolite production.Filamentous fungi from regions with extreme conditions present physiological adaptations that result inmetabolic pathways able for producing novel molecules with antimicrobial activity encoded in geneclusters 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 secondarymetabolites production profile of a strain of the Antarctic fungi Cadophora malorum was evaluated. Thefungus was cultivated in potato dextrose medium (PD) in solid (PDA), liquid (PDB), and inert solid(Polyutertane foam) under different temperatures (5, 10, and 15°C) and agitation conditions (static and200 rpm). Additionally, the effect of mechanical damage to the mycelia was evaluated. After 28 days ofculture, the biomass-free culture supernatant was extracted with ethyl acetate; the organic phase wasevaporated and resuspended in methanol to evaluate their antifungal activity against a set offilamentous fungi and yeasts of clinical relevance using the Kirby-Bauer technique. Also, RP-HPLC analysisof the extracts was done to compare metabolite profiles. Different levels of antifungal activity, expressedas inhibition diameter (ID, cm), were observed. The highest inhibition was obtained from cultures growingunder 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 ofCycloheximide (10 mg/ml) was used showing the following ID (1.08±0,04, 1.98±0,11, 2.95±0.70, 3.1±0.5respectively). 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 wereobserved. Rhizopus sp showed no inhibition when challenged with extracts obtained from all the testedconditions.These results highlighted the relevance of exploring fungal culture and environmental conditions whenlooking for particular bioactivity. The procedure present in this summary is going to be applied to continueexploring the metabolic diversity of Antarctic fungi.