Differential Gene Expression Analysis of Aspergillus terreus Reveals Metabolic Response and Transcription Suppression under Dissolved Oxygen and pH Stress

Aspergillus terreus, an acid tolerant fungus that grows over a wide range of pH from 2 to 8, was employed in this study. Submerged fermentation was conducted under low dissolved oxygen (10% DO) and pH (pH 2). The fermentation kinetics was investigated together with transcriptome to identify key genes associated with metabolic responses to such environmental stresses by high-throughput RNA-seq technology. It was clear that under low dissolved oxygen, glycolysis was uncoupled from oxidative phosphorylation due to limited ATP regeneration, as observed from the downregulation of genes in the mitochondrial respiratory chain complex and slow growth. On the contrary, the transcriptional levels of genes encoding ATPases and cation transporters remained unchanged at –1 ≤ log2 fold change ≤ 1, revealing that A. terreus possessed an excellent defense mechanism to low pH. In addition, genes associated with cell wall synthesis and repair, including chitin synthase and 1,3-beta-glucan synthase genes, and genes in the cluster for cell wall protection and repair were upregulated. This evidence clearly demonstrated that A. terreus was able to survive under the acidic environment. In summary, we comprehensively analyzed and discussed the transcriptome of A. terreus. The findings obtained here provide a theoretical basis for better understaning the molecular mechanism of the fungal response to the environmental factors, providing thereby an insight into the process of designing and optimizing the production of biological products of interest. This approach can be applicable to other metabolic pathways of interest in particular microorganisms.