Objective To elucidate the tolerance mechanisms of Penicillium oxalicum Z2 to flavonoids present in licorice residues and to analyze its transcriptional responses under gradient stress concentrations, thereby providing a theoretical basis for breeding resistant strains and improving fermentation efficiency. Methods P. oxalicum Z2 was treated with different concentrations of licorice flavonoids (0, 0.25, 0.50, 1.00, and 2.00 mg/mL). Physiological indicators were systematically measured. Transcriptome sequencing was conducted to identify differentially expressed genes and enriched KEGG/GO pathways, revealing the molecular adaptation mechanisms of P. oxalicum Z2 under flavonoid stress. Results As the flavonoid concentration increased, P. oxalicum Z2 maintained high biomass and cellulase activity. Under the highest flavonoid concentration (2.00 mg/mL), its biomass reached 4.840 g/L, and the activities of endoglucanase, β-glucosidase, filter paper enzyme, and xylanase reached 74.78, 3.24, 6.99, and 562.5 U/mL, respectively, which were more than ten folds of those in the conventional P. oxalicum strain. Transcriptome analysis showed that the number of differentially expressed genes increased in a concentration-dependent manner, from 818 in the Low group to 3 945 in the Super group. Under low stress (≤1.00 mg/mL), the strain reprogrammed carbohydrate metabolism and ABC transporter pathways to adjust carbon utilization and sustain essential cellular activities. Under high stress (2.00 mg/mL), it further activated the ribosome and oxidative phosphorylation pathways, with 65 genes upregulated in the ribosome pathway. Conclusion This study identified key genes (e.g., EF-Tu, SecY,and FtsY) and core pathways (e.g., oxidative phosphorylation and ABC transporter), demonstrating that P. oxalicum Z2 employed tiered responses to licorice flavonoid stress. Specifically, the strain remodels sugar metabolism and transmembrane transport under low flavonoid stress to maintain survival and activates ribosome and energy metabolism compensation mechanisms under high flavonoid stress.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |