Isolation and identification of Monascus strains and its degradation treatment of pit bottom wastewater of the sauce-flavor Baijiu byproduct

To obtain Monascus spp. with high efficiency in degrading pit bottom wastewater from sauce-flavor (Jiangxiangxing) Baijiu production, Monascus strains were screened from sauce-flavor Baijiu Daqu using traditional cultivation methods and identified through morphological observation and molecular biology techniques. The growth capacity of Monascus was evaluated with biomass. The degradation of organic pollutants and the effects of fermentation pit bottom wastewater on lovastatin and γ-aminobutyric acid production of screened strains were investigated, and the synthesis mechanism of high value-added metabolites was analyzed. The results showed that the isolated strains HSHM, AKHM, ZSHM and CMHM were identified as Monascus ruber, Monascus anka, Monascus purpureus, and Monascus pilosus, respectively. Strain ZSHM exhibited the highest biomass (0.098±0.016 g/L) and achieved removal rates of 56.76% biochemical oxygen demand (BOD₅) and 67.63% chemical oxygen demand (COD_cr) indextrose broth medium supplemented with 10% (V/V) pit bottom wastewater. When strain ZSHM was fermented in rice and sorghum substrates, the yields of lovastatin and γ-aminobutyric acid were (23.26±2.08) mg/100 g, (34.27±0.29) mg/100 g and (53.67±0.74) mg/100 g, and (43.66±0.75) mg/100 g, respectively. After adding pit bottom wastewater 10% (V/V) to rice and sorghum substrate, lovastatin yield were significantly reduced to (16.56±0.71) mg/100 g and (35.16±2.08) mg/100 g (P<0.05), and γ-aminobutyric acid yield were significantly increased to (42.58±1.68) mg/100 g and (57.12±1.31) mg/100 g (P<0.05). Transcriptomic analysis revealed that pit bottom wastewater enriched γ-aminobutyric acid by significantly up-regulating genes expression of GAD, GDH2, ALDH, and aofH.