Culture Conditions Shape the Phenotype and Quality of Talaromyces sayulitensis HC1 Conidia

This study evaluated how culture system and culture medium composition influence the phenotype and functional quality of Talaromyces sayulitensis HC1 conidia. Conidia were produced by solid-state fermentation (SSF) and submerged fermentation (SmF) using two culture medium compositions differing in sucrose and ammonium phosphate concentrations and, consequently, in C:N ratio. Morphological, ultrastructural, physicochemical and functional attributes were analyzed together with the expression of four selected conidiation-related genes (brlA, abaA, fluG and rodA). Conidia produced under SSF were significantly smaller and displayed a more cylindrical morphology and accumulated significantly more melanin than those produced under SmF, whereas SmF-derived conidia exhibited significantly higher relative ergosterol content. Outer cell wall thickness was significantly influenced by both culture system and culture medium composition. Across both culture systems, the medium containing a lower sucrose concentration and a higher ammonium phosphate concentration (C:N ratio 10:1) resulted in significantly higher germination but significantly lower thermotolerance than the medium containing a higher sucrose concentration and a lower ammonium phosphate concentration (C:N ratio 50:1). The medium was also associated with significantly greater melanization. Expression of brlA, abaA, fluG and rodA was generally higher under SSF, although the magnitude of the response varied among genes and culture medium compositions. The integrated analysis revealed that germination and thermotolerance were not necessarily coupled and that culture system and culture medium composition influenced different dimensions of conidial quality. The main innovation of this study is the integration of structural, physicochemical, functional and selected molecular indicators to identify distinct conidial quality profiles relevant to application-oriented production of fungal inoculants.