Liu Jiao, Yao Changhong, Meng Yingying, Cao Xupeng, Wu Peichun, Xue Song
1Marine Bioengineering Group, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 16023 China.
2University of Chinese Academy of Sciences, Beijing, 100049 China.
Biotechnol Biofuels. 2018 Jun 20;11:168. doi: 10.1186/s13068-018-1168-y. eCollection 2018.
Triacylglycerol (TAG) from photosynthetic microalgae is a sustainable feedstock for biodiesel production. Physiological stress triggers microalgal TAG accumulation. However excessive physiological stress will impair the photosynthesis system seriously thus decreasing TAG productivity because of the low biomass production. Hence, it is critical to quantitatively and timely monitor the degree of the stress while the microalgal cells growing so that the optimal TAG productivity can be obtained.
The lack of an on-line monitored indicator has limited our ability to gain knowledge of cellular "health status" information regarding high TAG productivity. Therefore, to monitor the degree of nitrogen stress of the cells, we investigated the correlation between the photosynthetic system II (PS II) quantum yield and the degree of stress based on the high relevancy between photosynthetic reduction and nitrogen stress-induced TAG accumulation in microalgal cells. Δ', which is the chlorophyll fluorescence parameter that reflects the effective capability of PS II, was identified to be a critical factor to indicate the degree of stress of the cells. In addition, the concept of a nitrogen stress index has been defined to quantify the degree of stress. Based on this index and by monitoring Δ' and guiding the supply of nitrogen in culture medium to maintain a stable degree of stress, a stable and efficient semi-continuous process for TAG production has been established.
The results indicate that the semi-continuous cultivation process with a controlled degree of stress by monitoring the Δ' indicator will have a significant impact on microalgal TAG production, especially for the outdoor controllable cultivation of microalgae on a large scale.
来自光合微藻的三酰甘油（TAG）是生物柴油生产的可持续原料。生理胁迫会触发微藻TAG积累。然而，过度的生理胁迫会严重损害光合作用系统，从而由于生物量产量低而降低TAG生产力。因此，在微藻细胞生长过程中定量及时地监测胁迫程度至关重要，这样才能获得最佳的TAG生产力。
缺乏在线监测指标限制了我们获取有关高TAG生产力的细胞“健康状态”信息的能力。因此，为了监测细胞的氮胁迫程度，基于光合还原与微藻细胞中氮胁迫诱导的TAG积累之间的高度相关性，我们研究了光合系统II（PS II）量子产率与胁迫程度之间的相关性。Δ'，即反映PS II有效能力的叶绿素荧光参数，被确定为指示细胞胁迫程度的关键因素。此外，还定义了氮胁迫指数的概念来量化胁迫程度。基于该指数，通过监测Δ'并指导培养基中氮的供应以维持稳定的胁迫程度，建立了稳定高效的TAG半连续生产工艺。
结果表明，通过监测Δ'指标控制胁迫程度的半连续培养过程将对微藻TAG生产产生重大影响，特别是对于大规模室外可控微藻培养。
