Improved production of docosahexaenoic acid in batch fermentation by newly-isolated strains of Schizochytrium sp.and Thraustochytriidae sp.through bioprocess optimization

Thraustochytrids,rich in docosahexaenoic acid(DHA,C22:6u3),represent a potential source of dietary fatty acids.Yet,the effect of culture conditions on growth and fatty acid composition vary widely among different thraustochytrid strains.Two different thraustochytrid strains,Schizochytrium sp.PKU#Mn4 and Thraustochytriidae sp.PKU#Mn16 were studied for their growth and DHA production characteristics under various culture conditions.Although they exhibited similar fatty acid profiles,PKU#Mn4 seemed a good candidate for industrial DHA fermentation while PKU#Mn16 displayed growth tolerance to a wide range of process conditions.Relative DHA content of 48.5%and 49.2%(relative to total fatty acids),respectively,were achieved on glycerol under their optimal flask culture conditions.Maximum DHA yield(Yp/x)of 21.0%and 18.9%and productivity of 27.6 mg/L-h and 31.9 mg/L-h were obtained,respectively,in 5-L bioreactor fermentation operated with optimal conditions and dual oxygen control strategy.A 3.4-and 2.8-fold improvement of DHA production(g/L),respectively,was achieved in this study.Overall,our study provides the potential of two thraustochytrid strains and their culture conditions for efficient production of DHA-rich oil.

大洋最小含氧带生物地球化学循环及微生物多样性研究进展

大洋的最小含氧带(oxygen minimum zones,OMZs)具有特殊的水动力和氧含量特征,该区域是氮流失的主要场所,也是各类生化反应发生的重要区域。OMZs的存在会对浮游生物的丰度、多样性、分布模式及呼吸方式产生较大影响。大洋OMZs中存在广泛的反硝化、厌氧氨氧化、甲烷厌氧氧化和隐性厌氧硫氧化作用等都是海洋物质循环的关键环节。全球海洋OMZs的规模在人类活动和全球变暖等因素的影响下也呈现出逐渐扩大的趋势。低氧环境的变化可以通过微生物多样性和群落结构稳定性进行判断,因此了解该区域的多样性水平是十分必要的。现有研究虽然对海洋OMZs的生物地球化学循环、微生物多样性和生态效应有了一定的认识,但对该区域总体情况和微生物生态学研究现状的系统性综合论述还较少,对海洋低氧环境的微生物活性、群落结构稳定性和分子代谢过程的研究还有较大的探讨空间。本文介绍了海洋低氧环境的分布情况和生态环境效应,全面且详细地论述了OMZs内各物质循环过程和微生物多样性的研究现状,指出尚未很好解决的生态学问题。