Transcriptomic Analysis Insights into Salt Adaptation of Pickle-Derived Aspergillus westerdijkiae

Aspergillus westerdijkiae, a filamentous fungus commonly isolated from pickled vegetables and high-salt condiments, can cause spoilage and produce nephrotoxic ochratoxin A (OTA) under saline conditions. However, its adaptive mechanisms to salt stress remain unclear. To address this, the pickle-derived strain NDX1 was subjected to 0, 1.0, 1.5, and 2.0 mol/L NaCl treatments. Colony growth was assessed after 7 days of incubation on PDA plates supplemented with the respective NaCl concentrations. For physiological indices, mycelia were pre-cultured in salt-free PDB for 5 days, followed by the addition of NaCl to final concentrations (0, 1.0, 1.5, and 2.0 mol/L) and further incubation for 2 days, after which relative electrical conductivity (REC) and malondialdehyde (MDA) content were measured. Colony diameters were recorded to evaluate vegetative growth; REC was determined by conductometry to assess cell membrane permeability; and MDA content was measured via the thiobarbituric acid (TBA) colorimetric method to indicate lipid peroxidation levels. Transcriptome sequencing combined with qRT-PCR validation was employed to identify differentially expressed genes (DEGs) involved in osmotic adaptation. Results showed that low salinity (1.0 mol/L NaCl) promoted growth, while higher concentrations (≥1.5 mol/L NaCl) inhibited it, accompanied by increased REC and decreased MDA, forming a distinctive high-permeability, low-lipid-peroxidation phenotype. A total of 3155 DEGs were detected, mainly associated with the HOG-MAPK cascade, glycerol biosynthesis, and ion transport pathways. Eight key HOG-MAPK genes and 21 glycerol metabolic genes were upregulated in a concentration-dependent manner, with the terminal kinase Hog1 coordinating transcription of downstream effectors governing glycerol synthesis and ion homeostasis. These findings demonstrate that A. westerdijkiae integrates de novo glycerol production and intracellular lipid remodeling via the HOG-MAPK pathway to achieve osmotic adaptation under hypersaline stress. This work identifies potential molecular targets for controlling toxigenic spoilage caused by this species in high-salt fermented foods.