Fan Jianhua, Zheng Lvhong, Bai Yunpeng, Saroussi Shai, Grossman Arthur R
State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China.
Department of Applied Biology, East China University of Science and Technology, Shanghai, China.
Front Plant Sci. 2017 Nov 20;8:1997. doi: 10.3389/fpls.2017.01997. eCollection 2017.
Concentrating algal cells by flocculation as a prelude to centrifugation could significantly reduce the energy and cost of harvesting the algae. However, how variation in phenotypic traits such as cell surface features, cell size and motility alter the efficiency of metal cation and pH-induced flocculation is not well understood. Our results demonstrate that both wild-type and cell wall-deficient strains of the green unicellular alga efficiently flocculate (>90%) at an elevated pH of the medium (pH 11) upon the addition of divalent cations such as calcium and magnesium (>5 mM). The trivalent ferric cation (at 10 mM) proved to be essential for promoting flocculation under weak alkaline conditions (pH ∼8.5), with a maximum efficiency that exceeded 95 and 85% for wild-type CC1690 and the cell wall-deficient mutant, respectively. Near complete flocculation could be achieved using a combination of 5 mM calcium and a pH >11, while the medium recovered following cell removal could be re-cycled without affecting algal growth rates. Moreover, the absence of starch in the cell had little overall impact on flocculation efficiency. These findings contribute to our understanding of flocculation in different Chlamydomonas strains and have implications with respect to inexpensive methods for harvesting algae with different phenotypic traits. Additional research on the conditions (e.g., pH and metal ions) used for efficient flocculation of diverse algal groups with diverse characteristics, at both small and large scale, will help establish inexpensive procedures for harvesting cell biomass.
通过絮凝浓缩藻类细胞作为离心的前奏，可以显著降低收获藻类的能量和成本。然而，细胞表面特征、细胞大小和运动性等表型特征的变化如何改变金属阳离子和pH诱导的絮凝效率，目前还不太清楚。我们的结果表明，绿色单细胞藻类的野生型和细胞壁缺陷型菌株在添加钙和镁等二价阳离子（>5 mM）后，在培养基pH升高（pH 11）时均能高效絮凝（>90%）。三价铁阳离子（10 mM）被证明是在弱碱性条件（pH ∼8.5）下促进絮凝所必需的，野生型CC1690和细胞壁缺陷型突变体的最大絮凝效率分别超过95%和85%。使用5 mM钙和pH>11的组合可以实现近乎完全的絮凝，并且细胞去除后回收的培养基可以循环使用而不影响藻类生长速率。此外，细胞中淀粉的缺失对絮凝效率总体影响不大。这些发现有助于我们理解不同衣藻菌株中的絮凝现象，并对采用不同表型特征的藻类进行廉价收获的方法具有启示意义。对用于不同特征的不同藻类群体高效絮凝的条件（如pH和金属离子）进行更多的小规模和大规模研究，将有助于建立廉价的细胞生物质收获程序。
