ε-聚赖氨酸(ε-poly-L-lysine,ε-PL)是一种通过微生物发酵法生产的同型氨基酸聚合物。为了提高Streptomyces albulus GS114的ε-PL发酵产量,建立了一种基于动态pH值调控溶氧水平的发酵策略,并从氧化损伤与抗氧化角度对该策略提高ε-PL发酵产量的原因进行了初步解析。研究发现,在发酵中后期通过调节pH值来控制溶氧水平保持在20%~40%,实现了菌体干重达到62.03 g/L,ε-PL产量达到60.2 g/L,分别比未调控提高了59%和36%。对S.albulus GS114胞内氧化损伤和抗氧化能力进行分析发现,采用该调控策略一方面增加了菌体胞内活性氧水平,另一方面也增强了菌体的总抗氧化能力。不同pH发酵过程的菌体胞内活性氧水平、氧化损伤程度和总抗氧化能力分析发现,菌体生长、活性氧水平、氧化损伤程度和总抗氧化能力均与pH值呈正相关。因此,动态调节pH值策略显著增强菌体生长的同时,带来了菌体胞内活性氧水平、氧化损伤程度和总抗氧化能力的提高,但菌体的总抗氧化能力实现了活性氧水平和氧化损伤维持在适当水平,进而促进了ε-PL在发酵中后期的生物合成。该研究不仅对提升工业发酵ε-PL水平具有实际指导意义,且初步发现了活性氧对促进ε-PL生物合成的潜在作用。
ε-Poly-L-lysine (ε-PL) is a homopoly(amino acid) produced by microbial fermentation. In order to improve the production of ε-PL of Streptomyces albulus GS114, a fermentation strategy based on dynamic pH value to regulate the level of dissolved oxygen was established, oxidative damage and antioxidation were used to explore the reasons of improved ε-PL production. The dry cell weight of S. albulus GS114 reached 62.03 g/L and the production of ε-PL reached 60.2 g/L, which were 59% and 36% higher than that without regulation, respectively, through the controlling of dissolved oxygen level at 20%-40% by adjusting pH value in the middle and late stages of fermentation. By analyzing the intracellular oxidative damage and antioxidation of S. albulus GS114, it was found that the developed strategy not only increased the level of intracellular reactive oxygen species, but also enhanced the total antioxidation capacity. Moreover, the cell growth, reactive oxygen species level, oxidative damage and total antioxidation capacity were positively correlated with pH values. As a result, the developed strategy significantly enhanced the cell growth, while the level of intracellular reactive oxygen species, oxidative damage and the total antioxidation capacity were also improved. However, the total antioxidation capacity of the bacteria kept the level of reactive oxygen species and oxidative damage at an appropriate level, and thus promoted the biosynthesis of ε-PL in the middle and late stages of fermentation. The study not only provides a strategy for improving the ε-PL production of industrial fermentation, but also finds the potential role of reactive oxygen species in promoting the biosynthesis of ε-PL.
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