The First Record of Cleistothecial Thermoascus crustaceus isolated from Dried Hardwood Pulp in Korea

Radish-brown spots of fungal contamination was detected on dried hardwood pulp sheets during storage at a paper manufacturing company in Korea. Therefore, this study was conducted to identify and characterize the fungal contaminant responsible for the discoloration observed in the stored hardwood pulp sheets. A new thermophilic cleistothecial fungal isolate recovered from these affected regions was identified as Thermoascus crustaceus by sequencing of the partial D1-D2 region of the long rRNA gene, which exhibited 100% identity with the reference strains JF922031.1, FJ358289.1, and EU021597.1. Morphological analyses by light microscopy revealed prolific conidial clusters and extensive hyphal networks colonizing the discolored hardwood pulp surfaces. The isolate demonstrated optimal growth at 50°C, consistent with adaptation to the high processing temperatures used during papermaking. This study reports the first documented isolation of T. crustaceus related to fungal contamination and discoloration in hardwood pulp sheets from Korea and emphasizes the ecological and industrial significance of thermophilic Ascomycota in high-temperature manufacturing environments.