Wang Song, Zhou Xiyi, Wu Sha, Zhao Mengkai, Hu Zhangli
Guangdong Technology Research Center for Marine Algal Bioengineering; Guangdong Provincial Key Laboratory for Plant Epigenetics; Shenzhen Engineering Laboratory for Marine Algal Biotechnology; Longhua Innovation Institute for Biotechnology; College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, 518060, China.
College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen, 518060, China.
Biotechnol Biofuels Bioprod. 2023 May 19;16(1):84. doi: 10.1186/s13068-023-02338-8.
Diatoms have been viewed as ideal cell factories for production of some high-value bioactive metabolites, such as fucoxanthin, but their applications are restrained by limited biomass yield. Mixotrophy, by using both CO and organic carbon source, is believed effective to crack the bottleneck of biomass accumulation and achieve a sustainable bioproduct supply.
Glycerol, among tested carbon sources, was proved as the sole that could significantly promote growth of Cylindrotheca sp. with illumination, a so-called growth pattern, mixotrophy. Biomass and fucoxanthin yields of Cylindrotheca sp., grown in medium with glycerol (2 g L), was increased by 52% and 29%, respectively, as compared to the autotrophic culture (control) without compromise in photosynthetic performance. As Cylindrotheca sp. was unable to use glycerol without light, a time-series transcriptomic analysis was carried out to elucidate the light regulation on glycerol utilization. Among the genes participating in glycerol utilization, GPDH1, TIM1 and GAPDH1, showed the highest dependence on light. Their expressions decreased dramatically when the alga was transferred from light into darkness. Despite the reduced glycerol uptake in the dark, expressions of genes associating with pyrimidine metabolism and DNA replication were upregulated when Cylindrotheca sp. was cultured mixotrophically. Comparative transcriptomic and metabolomic analyses revealed amino acids and aminoacyl-tRNA metabolisms were enhanced at different timepoints of diurnal cycles in mixotrophic Cylindrotheca sp., as compared to the control.
Conclusively, this study not only provides an alternative for large-scale cultivation of Cylindrotheca, but also pinpoints the limiting enzymes subject to further metabolic manipulation. Most importantly, the novel insights in this study should aid to understand the mechanism of biomass promotion in mixotrophic Cylindrotheca sp.
硅藻被视为生产某些高价值生物活性代谢物（如岩藻黄质）的理想细胞工厂，但其应用受到生物量产量有限的限制。混合营养通过同时利用二氧化碳和有机碳源，被认为是打破生物量积累瓶颈并实现可持续生物产品供应的有效方法。
在测试的碳源中，甘油被证明是唯一能在光照条件下显著促进圆柱鞘丝藻生长的碳源，即所谓的混合营养生长模式。与无光合性能受损的自养培养（对照）相比，在含有甘油（2 g/L）的培养基中生长的圆柱鞘丝藻的生物量和岩藻黄质产量分别提高了52%和29%。由于圆柱鞘丝藻在无光条件下无法利用甘油，因此进行了时间序列转录组分析以阐明光照对甘油利用的调节作用。在参与甘油利用的基因中，GPDH1、TIM1和GAPDH1对光照的依赖性最高。当藻类从光照转移到黑暗中时，它们的表达急剧下降。尽管在黑暗中甘油摄取减少，但当圆柱鞘丝藻进行混合营养培养时，与嘧啶代谢和DNA复制相关的基因表达上调。比较转录组学和代谢组学分析表明，与对照相比，混合营养的圆柱鞘丝藻在昼夜循环的不同时间点氨基酸和氨酰-tRNA代谢增强。
总之，本研究不仅为圆柱鞘丝藻的大规模培养提供了一种替代方法，还指出了有待进一步代谢调控的限速酶。最重要的是，本研究中的新见解应有助于理解混合营养的圆柱鞘丝藻中生物量促进的机制。
