Transcriptome analysis of Ochratoxin a (OTA) producing <italic>Aspergillus westerdijkiae</italic> fc-1 under varying osmotic pressure.

Ochratoxin A (OTA) is a toxic secondary metabolite produced by the <italic>Aspergillus</italic> species which can contaminate various food products. This study analysed the transcriptome of the <italic>Aspergillus westerdijkiae</italic> fc-1 strain under NaCl concentrations of 0, 20, and 100 g/L using RNA-Seq technology to examine gene transcriptional changes linked to osmotic stress and OTA production. Significant changes were observed in metabolic-pathways associated with carbohydrates, cellular communication, and hydrolase activity under 20 g/L NaCl. The <italic>HOG1</italic> gene, associated with osmotic pressure regulation was down-regulated by 78.06%. In contrast, OTA biosynthesis genes <italic>otaA</italic>, <italic>otaB</italic>, and <italic>otaC</italic> were up-regulated by 3.26 fold, 1.99 fold, and 2.06 fold, respectively. Conversely, the <italic>otaD</italic> gene was down-regulated by 43.50%. At 100 g/L NaCl, pathways related to ion transport, peptide metabolism, ribosomal function, and transmembrane transporter protein activities were significantly up-regulated. The <italic>HOG1</italic> gene was up-regulated by 28.32% and OTA biosynthesis genes <italic>otaA</italic>, <italic>otaB</italic>, <italic>otaC</italic>, and <italic>otaD</italic> showed up-regulation of 27.06%, 36.80%, 19.59%, and 5.72 fold, respectively. The study highlights the role of metabolic pathways in osmotic stress regulation and the correlations between <italic>HOG1</italic> expression and OTA biosynthesis genes, providing insights for developing strategies to prevent OTA contamination in food. [ABSTRACT FROM AUTHOR]