Abstract BACKGROUND Fungi from aquatic environments, such as caves and hot springs, are promising sources of novel enzymes with significant biotechnological potential, particularly amylases (EC 3.2.1.1) Despite their relevance, members of the genus Halobyssothecium have been rarely reported and their enzymatic potential remains unexplored. The present study aimed to isolate and characterize a thermotolerant fungal strain from thermal caves and to evaluate its ability to produce amylases under different fermentation conditions. Microorganisms exposed to extreme climatic and geographic conditions represent an underexplored source of enzymatic diversity within fungal microbiota, offering valuable insights into their metabolic capabilities and potential biotechnological applications. RESULTS A fungal isolate identified as Halobyssothecium cf. unicellulare was obtained from sediment samples. Morphological and molecular analyses, including ITS sequencing and phylogenetic reconstruction, confirmed its close affiliation with H. unicellulare . Pellet formation in submerged culture showed an inverse relationship between inoculum size and pellet diameter. Low inoculum levels produced fewer, larger pellets, whereas higher inoculum amounts generated a greater number of smaller pellets, indicating that inoculum size strongly influences pellet morphology. Qualitative assays revealed high amylolytic activity on a solid medium, with enzymatic indices above 1.9 even under saline conditions (10% NaCl), suggesting halotolerance. Extracellular amylase production was evaluated under solid‐state fermentation (SSF) and submerged fermentation (SmF). The highest volumetric activity (8.25 U/mL) and specific activity (20.54 U/mg) were obtained under SSF at 45 °C on day 10—approximately 446‐fold higher than the specific activity observed under SmF at the same time point (0.046 U/mg). CONCLUSION This study reports, for the first time, the amylolytic potential of Halobyssothecium cf. unicellulare . The marked thermotolerant and halotolerant properties of its extracellular amylases highlight the relevance of this genus as a novel source of industrially valuable enzymes, advancing the search for robust biocatalysts from extreme aquatic environments. © 2026 Society of Chemical Industry (SCI).
Legorreta‐Castañeda et al. (Fri,) studied this question.