Thermal adaptation in a marine-derived tropical strain of Fusarium equiseti and polar strains of Pseudogymnoascus spp. under different nutrient sources

We documented relative growth rates (RGRs) and activities of extracellular hydrolytic enzymes (EHEs) of one marine-derived tropical strain of Fusarium equiseti originally isolated from Malaysia and two polar strains of Pseudogymnoascus spp. from the Arctic and Antarctic under various temperatures and different nutrient conditions. RGRs and relative enzyme activities (RAs) of protease, amylase and cellulase were screened in seawater nutrient assay plates augmented with either skim milk, soluble starch or carboxymethylcellulose with trypan blue, respectively, across culture temperatures between 5°C and 40°C. Measures of RGR were fitted into third-degree polynomial and Brière-2 temperature-dependent models to estimate optimum temperatures for growth (Topt) and maximum growth rates (RGRmax), and were used to calculate temperature coefficients (Q10) and activation energies (Ea) for growth. All studied strains showed highest RGR and RA when grown using a skim milk nutrient assay. Topt for growth was 25°C in F. equiseti and 20°C in Pseudogymnoascus spp. Only F. equiseti showed cellulase activity. These data suggest a preference for protein-based substrates over plant-derived substrates for metabolism in these fungal strains. The tropical F. equiseti could utilise higher levels of thermal energy for growth than the polar strains of Pseudogymnoascus spp., implying adaptation of these fungi to different bioclimatic regions.