Abstract

Monascus pigments (MPs) are widely used natural colorants in Asian countries. The problems of low extracellular red pigment (ERP) and high citrinin remain to be solved in Monascus pigment production. The effect of lanthanum(III) ion (LaCl₃) on Monascus purpureus fermentation was investigated in this study. The yields of ERP and biomass respectively reached maxima of 124.10 U/mL and 33.10 g/L by adding 0.4 g/L La³⁺ on the second day in the total 8-day fermentation; simultaneously, citrinin was decreased by 59.93% and 38.14% in the extracellular and intracellular fractions, respectively. Reactive oxygen species (ROS) levels were obviously improved by La³⁺ treatment, while the activities of catalase (CAT) and superoxide dismutase (SOD) were increased compared with the control. The ratio of unsaturated/saturated fatty acids in mycelia was increased from 2.94 to 3.49, indicating that the permeability and fluidity of the cell membrane were enhanced under La³⁺ treatment. Gene expression analysis showed that the relative expression levels of Monascus pigment synthesis genes (pksPT, mppB, mppD, MpFasB2, and MpPKS5) were significantly upregulated by La³⁺ treatment, and in contrast, the relative expression levels of citrinin synthesis genes (ctnA, pksCT and mppC) were markedly downregulated. This work confirmed that LaCl₃ possesses the potential to induce red pigment biosynthesis and inhibit citrinin production in M. purpureus fermentation.

Key points

• La ³⁺ induced red pigment and inhibited citrinin production in Monascus fermentation.

• La ³⁺ regulated genes expression up for Monascus pigment and down for citrinin.

• La ³⁺ increased the UFAs in cell membrane to enhance the permeability and fluidity.

中文翻译：

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在紫红曲霉发酵中加入镧（III）离子诱导红色素并抑制柠檬素生成

摘要

红曲霉颜料（MPs）是亚洲国家广泛使用的天然着色剂。在红曲色素的生产中，细胞外红色素低（ERP）和柠檬绿素高的问题仍有待解决。本研究研究了镧（III）离子（LaCl ₃）对红曲霉发酵的影响。在总共8天的发酵的第二天，通过添加0.4 g / L La ³⁺，ERP和生物质的产量分别达到124.10 U / mL和33.10 g / L的最大值。同时，胞外和胞内成分中的柠檬绿素分别降低了59.93％和38.14％。La ³⁺明显提高了活性氧（ROS）水平与对照组相比，过氧化氢酶（CAT）和超氧化物歧化酶（SOD）的活性增加了。菌丝体中不饱和/饱和脂肪酸的比例从2.94增加到3.49，表明在La ³⁺处理下细胞膜的通透性和流动性得到增强。基因表达分析表明，La ³⁺处理显着上调了红曲霉色素合成基因pksPT，mppB，mppD，MpFasB2和MpPKS5的相对表达水平，与此相反，柑桔素合成基因的相对表达水平ctnA，pksCT和mppC）明显下调。这项工作证实了LaCl ₃具有潜在的诱导红色色素生物合成和抑制紫癜分枝杆菌发酵中的柑桔生成的能力。

关键点

•La ³⁺ 在红曲菌发酵中诱导红色素并抑制柠檬素生成。

•La ³⁺ 调控的基因在红曲霉色素上表达，而在柑桔素中表达下调。

•La ³⁺ 增加了细胞膜中的UFA，以增强渗透性和流动性。