Response patterns of thermophilic Ascomycota to seasonal variations in Hammam Meskhoutine hot spring (Guelma, Algeria).

Hot spring microbial mats may host diverse and thermally adapted fungal communities. This study investigated the environmental factors controlling the seasonal distribution of culturable fungi at the Hammam Meskhoutine hot spring. Culture-dependent morphological and molecular analysis identified three Ascomycota species: Aspergillus fumigatus (311 colonies), Mycothermus thermophilus (79 colonies), and Thermomyces lanuginosus (5 colonies). Significant density fluctuations were observed for A. fumigatus (p < 0.001), which peaked in spring (13 × 105 CFU g- 1) before decreasing to a summer low (6 × 103 CFU g- 1). M. thermophilus showed a similar pattern (p = 0.049), reaching its maximum in winter (11 × 103 CFU g- 1) and a minimum in summer (2.2 × 102 CFU g- 1). Principal component analysis indicated that a combination of macronutrients, trace elements, and physical and chemical parameters strongly correlate with this spatiotemporal occurrence. In vitro assays confirmed that temperature strictly dictates growth rates (Friedman test, p < 0.001), defining clear thermal optima: 37 °C for A. fumigatus 50 °C for M. thermophilus, and 55 °C for T. lanuginosus, and thereby determining the ecological distribution of each isolate by shaping their distinct thermal niches. Furthermore, pH variations modulated these thermal preferences; notably, acidic conditions slowed M. thermophilus growth rates to 2.729 ± 1.82 mm days- 1 even at its 37 °C optimum. More specifically, our observations suggest that the chemistry and temperature of the studied thermal water interact and affect the distribution patterns of the culturable fungi, and likely non-culturable fungi as well, within the same communities.