Transcriptomics Integrated with Metabolomics: Assessing the Central Metabolism of Different Cells after Cell Differentiation in Aureobasidium pullulans NG

Abstract

When organisms are stimulated by external stresses, oxidative stress is induced, resulting in the production of large amounts of reactive oxygen species (ROS) that inhibit cell growth and accelerate cellular aging until death. Understanding the molecular mechanisms of abiotic stress is important to enhance cellular resistance, and Aureobasidium pullulans, a highly resistant yeast-like fungus, can use cellular differentiation to resist environmental stress. Here, swollen cells (SCs) from two different differentiation periods in Aureobasidium pullulans NG showed significantly higher antioxidant capacity and stress defense capacity than yeast-like cells (YL). The transcriptome and the metabolome of both cells were analyzed, and the results showed that amino acid metabolism, carbohydrate metabolism, and lipid metabolism were significantly enriched in SCs. Glyoxylate metabolism was significantly upregulated in carbohydrate metabolism, replacing the metabolic hub of the citric acid (TCA) cycle, helping to coordinate multiple metabolic pathways and playing an important role in the resistance of Aureobasidium pullulans NG to environmental stress. Finally, we obtained 10 key genes and two key metabolites in SCs, which provide valuable clues for subsequent validation. In conclusion, these results provide valuable information for assessing central metabolism-mediating oxidative stress in Aureobasidium pullulans NG, and also provide new ideas for exploring the pathways of eukaryotic resistance to abiotic stress.

Hyper-Production of Pullulan by a Novel Fungus of Aureobasidium melanogenum ZH27 through Batch Fermentation

“…Previous studies suggested that yeast-like cells can differentiate into swollen cells via the regulation of low pH values (<6.0) [ 22 ]. Figure 5 shows that the hyper-osmotic stress and low pH values (ultimately 3.57) ( Table S3 ) under the OC prompted the cells of strain ZH27 to form swollen cells earlier and more extensively than those under the IC.…”

“…Notably, most of the swollen cells under the OC contained 1-2 large vacuoles but the swollen cells with one vacuole were dominant after 48 h, whereas swollen cells under the IC had one large vacuole and several small ones (Figure 5). Previous studies suggested that yeast-like cells can differentiate into swollen cells via the regulation of low pH values (<6.0) [22]. Figure 5 shows that the hyper-osmotic stress and low pH values (ultimately 3.57) (Table S3) under the OC prompted the cells of strain ZH27 to form swollen cells earlier and more extensively than those under the IC.…”

“…These changes in cell differentiation and vacuole characteristics were likely influenced by variations in nutrients and pH values, impacting pullulan synthesis. Swollen cells emerged as a prominent cell type during pullulan synthesis in A. pullulans NG [ 40 ], exhibiting a robust stress defense and antioxidative capabilities compared with yeast-like cells [ 22 ]. As shown in Figure 5 , swollen cells under the OC seemed to have a stronger and more stable ability to withstand environmental stress, which may require for high levels of pullulan production.…”

“…Moreover, the pH is identified as another factor that influences cell morphology and pullulan yield [ 42 ]. Yeast-like cells as core cells mainly occurred at the beginning of cultivation with higher pH values (≥6.0), while low pH values induced the differentiation of yeast-like cells into swollen cells [ 22 ]. The regulation of pH values seems to be a crucial factor in determining the cell types during the cultivation period.…”

“…This resulted in an evident difference in vacuoles within swollen cells and delayed the formation of chlamydospores. However, a previous study proposed that the arthroconidia of A. melanogenum TN3-1 and numerous small vacuoles might allow for withstanding high Previous studies suggested that yeast-like cells can differentiate into swollen cells via the regulation of low pH values (<6.0) [22]. Figure 5 shows that the hyper-osmotic stress and low pH values (ultimately 3.57) (Table S3) under the OC prompted the cells of strain ZH27 to form swollen cells earlier and more extensively than those under the IC.…”