Improving microalgal oil collecting efficiency by pretreating the microalgal cell wall with destructive bacteria

•F. yaeyamensis was used to develop cell wall disruption method for microalgal cells.•The growth of F. yaeyamensis was affected by salt concentration and pH value.•The cell-wall destruction was associated with the activity of hydrolytic enzymes.•The cell disruption method enhanced oil extraction efficiency of the microalgae.

Converting microalgae oil into biodiesel is considered a promising route in the field of biofuel production. However, the cost of microalgae-based biodiesel is still too high to be economically feasible. The high cost of microalgae-based biodiesel is mainly a result of downstream processing, in particular from the extraction of oil out of the microalgal biomass. This study proposes a bacterial (enzymatic) destruction pretreatment of the microalgae cell wall to render the microalgal oil extraction more efficient. It has been found that the cell wall of microalgae can be modified if the microalgal biomass is co-cultured with an indigenous bacterial isolate Flammeovirga yaeyamensis in a salt concentration of 3% and a pH of 8.0. Following this treatment, the activities of some hydrolytic enzymes (i.e., amylase, cellulases, and xylanase) have been detected in the co-culture of F. yaeyamensis and the oil-rich microalga (Chlorella vulgaris ESP-1). The SEM micrographs clearly show specific damage to the microalgae cell wall caused by the bacterial treatment. We found that when the microalgae is pretreated with a concentrated co-culture supernatant (containing the hydrolytic enzymes), a nearly 100% increase in lipid extraction efficiency is obtained. The proposed bacterial disruption method seems to be an effective and environmentally friendly way of improving the efficiency of oil extraction and biofuel production from a microalgal biomass.