Microalgae cell disruption and lipid composition and recovery improvements induced by algicidal effects of bacteria

Converting microalgal lipids 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, especially economical and effective methods for microalgae cell wall breaking are still lacking. In this study, five algicidal bacteria and their cell-free supernatant were evaluated by the percentage of cell disruption and lipid extraction of Chlorella sp.. Results showed that both bacteria and supernatant could induce cell disruption of Chlorella sp. to release lipids. Among them, the supernatant of Aeromonas hydrophila showed the best effects both in terms of the percentage of cell disruption and lipid extraction, and the cell disruption percentage increased with the extension of co-culture time with A. hydrophila supernatant. The inoculation volume of co-culture ( A. hydrophila cell-free supernatant and Chlorella sp.) was explored, indicating that 10% volume ratio of A. hydrophila supernatant was identified as optimal proportion to improve lipid extraction. In addition, A. hydrophila supernatant showed obvious effects on the composition distribution of lipids extracted from Chlorella sp. that the fraction of unsaturated fatty acids decreased apparently, which would be beneficial to biodiesel production. The mechanism of microalgal cell disruption by A. hydrophila supernatant was further studied by scanning electron microscopy, ROS levels and antioxidant responses. This indicated that the cell morphology of Chlorella sp. changed dramatically with the time of co-culture with A. hydrophila supernatant.. These findings implied that algicidal properties of bacteria components are a promising tool for microalga cell disruption and lipid recovery, providing a new insight into the method for biofuel production.