Motility changes rather than EPS production shape aggregation of Chlamydomonas microsphaera in aquatic environment

Microalgal aggregation is a key for both microalgae harvesting and water purification, where changes in extracellular polymeric substance (EPS) secretion and cell motility changes are of core importance. In this study, we investigated the aggregation process of Chlamydomonas microsphaera confronting resource limitation and chlorine disinfection, and tried to compare changes in the magnitude of EPS secretion and cell motility. Results show that the presence of mild chlorine solution (0.20%) dose stimulated microalgal aggregation (with an aggregated to planktonic cells ratio of 3.2), with extracellular protein concentration and mean cell velocity reaching a maximum of 43.43 ± 0.01 mg/L and 201 ± 35 µm/s, respectively. These values are 71% and 191% higher than those of the control. Comparably, nutrient availability had only a limited impact on microalgal aggregation and was associated with mild EPS secretion and cell motility. Correlation analysis revealed a strong positive impact of cell motility (mean velocity) on microalgae aggregation, with little effect on EPS excretion. Together, these quantitative estimations may shed light on understanding the mechanisms of microalgae aggregation in aqueous systems, which could help future design and practical operation of source water pretreatment or microalgae harvesting.