定向驯化对异养蛋白核小球藻硒的耐受性及富集能力的影响

Effects of directional adaptation on selenium tolerance and accumulation of heterotrophic Chlorella pyrenoidosa

摘要:

硒(Se)是生物体必不可少的微量元素，硒缺乏会导致人产生克山病、大骨节病等疾病，缺硒也会给畜牧业带来巨大损失。目前的补硒产品存在硒含量和生物利用度低、安全性差等问题，而通过小球藻培养可获得生物利用度高、安全性好的有机硒，因此是非常有应用前景的补硒产品。首先，为了获得对硒的耐受性和富集能力更强的藻种，研究通过定向驯化的方式逐步提高培养基中Na₂SeO₃浓度来驯化蛋白核小球藻，并对驯化时间和驯化过程中Na₂SeO₃的浓度梯度进行了优化。结果表明，驯化后的藻种对硒的耐受性和富集能力明显提高。在5L发酵罐中，驯化后的藻株可以耐受40mg/L的Na₂SeO₃，胞内有机硒合成速率提高了175.6%。之后，在5L发酵罐中进一步优化了硒的补加方式，在异养培养过程中分批补料添加40mg/LNa₂SeO₃时，最终获得的蛋白核小球藻细胞干重达106.4g/L，有机硒含量为1227mg/kg，有机硒合成速率为1.36mg/(L·h)。研究结果与已有蛋白核小球藻异养富硒文献报道的最高细胞密度75g/L和最高有机硒含量560mg/kg相比分别提高了41.9%和119.1%。上述结果表明，通过定向驯化的方法，可大大提高蛋白核小球藻对硒的耐受性和富集能力。

Abstract:

Selenium (Se) is an essential trace element for organisms. Se deficiency will cause diseases such as Keshan disease and Kashin-Beck in human being, and huge loss to animal husbandry. Currently available Se supplements have such problems as low Se content, poor bioavailability, and poor safety. Chlorella pyrenoidosa can produce bioavailable and safe organic Se under suitable conditions, which is thus a promising Se supplement. Therefore, in this study, we tried to improve the Se tolerance and accumulation of C. pyrenoidosa by directional adaptation. To be specific, we gradually increased the concentration of Na₂SeO₃ in medium to domesticate C. pyrenoidosa and optimized the adapting time and concentration gradient of Na₂SeO₃ during the adaptation. The results showed that the adapted C. pyrenoidosa was more tolerant to Se and had stronger Se enrichment ability. In 5 L fermenter, the adapted strains could tolerate 40 mg/L Na₂SeO₃ and the synthesis rate of organic Se was 175.6% higher. Then, Se addition method in the 5 L fermenter was optimized. The result demonstrated that addition of Na₂SeO₃ at 40 mg/L during heterotrophic culture achieved the final dry weight of C. pyrenoidosa cells at 106.4 g/L, content of organic Se at 1 227 mg/kg, and synthesis rate of organic Se at 1.36 mg/(L·h). Compared with the reported highest cell density of 75 g/L and the highest organic Se content of 560 mg/kg, the corresponding figures in this study were 41.9% and 119.1% higher, respectively. In conclusion, directional adaptation can remarkably improve the Se tolerance and enrichment of C. pyrenoidosa.