Effect of extracellular polymeric substances on Dolichospermum aggregation during temperature rise

Dolichospermum, a typical model filamentous of cyanobacteria, has the potential to cause severely bloom. Extracellular polymeric substances (EPSs) are considered to influence the aggregation of the algae, and temperature is a significant factor affecting EPSs secretion. However, the mechanism of how EPSs affects the aggregation of Dolichospermum is still unclear because the structure and composition of EPSs are complex. In this study, the effects of EPSs on the aggregation of Dolichospermum during the rise of temperature (7-37 degrees C) were determined. The results showed that the concentration of extracellular polysaccharides and proteins changed significantly with increasing temperature (P<0.01). Firstly, during the increasing temperature, the polysaccharide content of EPSs increased from 20.34 to 54.64 mg/L, and the polysaccharides in the soluble EPS (S-EPS) layer changed significantly. The protein content reached maximum value at 21 degrees C (14.52 mg/L) and varied significantly in S-EPS and loosely bound EPS (LB-EPS). In the EPSs matrix, humus substances and protein were main components of S-EPS and LB-EPS, and protein was the main component of tightly bound EPS (TB-EPS). Secondly, the cell density of Dolichospermum increased during the temperature rise while the aggregation ratio decreased. Moreover, zeta potential and surface thermodynamic analysis of Dolichospermum revealed that the interfacial free energy and electrostatic repulsion increased gradually with increasing temperature, which further reduced the aggregation of Dolichospermum. Finally, principal component analysis (PCA) analysis showed the aggregation of Dolichospermum was directly related to the changes of protein in EPSs (especially S-EPS and LB-EPS) and zeta potential, and polysaccharides in EPSs inhibited the aggregation of Dolichospermum. Based on these results, it was illustrated that the composition and concentration of EPSs affected the cell surface properties of Dolichospermum with the change of temperature and thus affected the aggregation of Dolichospermum.

Automated summary

This study determined the effects of extracellular polymeric substances (EPSs) on the aggregation of Dolichospermum during temperature rise. The results showed that the composition and concentration of EPSs affected the cell surface properties of Dolichospermum and thus influenced its aggregation.