Mechanism behind autoflocculation of unicellular green microalgae Ettlia texensis

• Autoflocculation of E. texensis is due to glycoproteins patched to cell surface.
• ζ-Potential does not seem to attribute to autoflocculation of E. texensis.
• EPS play a predominant role in bio-flocculation of C. vulgaris and E. texensis.

The oleaginous Ettlia texensis is an autoflocculating green microalga that can be used for bio-flocculation of other microalgae species to facilitate harvesting. In this study the mechanism behind autoflocculation of E. texensis was revealed by scanning electron microscopy (SEM) analysis and by characterisation of the cell surface properties. SEM analysis and measurement of extracellular polymeric substances (EPS) showed that autoflocculation of E. texensis is due to the EPS containing mainly glycoproteins patched to the cell surface. Despite the presence of charged groups on the cell surface, they do not seem to attribute to autoflocculation of E. texensis. During bio-flocculation of E. texensis with Chlorella vulgaris EPS structures between both microalgal species were observed. EPS thus not only play a predominant role in autoflocculation of E. texensis but also in bio-flocculation when using this microalga to harvest others.