Pilot-scale isolation of bioactive extracellular polymeric substances from cell-free media of mass microalgal cultures using tangential-flow ultrafiltration

The commercial production of microalgae has become increasingly popular, but only algal biomass has been widely used whereas the vast amount of algae-free media has been essentially unexploited. However, a wide range of microalgae is known to release large amounts of extracellular polymeric substances (EPS) into their media. Therefore, we have attempted to isolate EPS using a coupled system of microfiltration and ultrafiltration from the spent culture media of both filamentous and unicellular microalgae, including cyanobacteria, green algae, red algae and diatoms. A high EPS isolation efficiency was achieved at a pilot-scale through optimization of the process parameters for the ultrafiltration of cell-free media. Because the scale-up of ultrafiltration is almost linear, it is practical to use the coupled system to isolate large quantities of EPS from the media of mass microalgal cultures. By using an in vitro cytotoxicity assay, we also reveal that the EPS isolated from the cell-free media of Nostoc sphaeroides and Haematococcus pluvialis were capable of inhibiting tumor cell growth. Together, these data demonstrate the feasibility of using ultrafiltration to isolate microalgal EPS with biomedical potentials from currently unused media of commercial algal cultures and, thus, provide an added value to the microalgal industry.