Promotion effect of bacteria in phycosphere on flocculation activity of Aspergillus niger on Synechocystis biomass

The cyanobacterium Synechocystis with high scientific research value and application potential to aquaculture is hard to harvest its biomass. Bioflocculation is an economical and efficient method for harvesting microalgal biomass. In this study, Aspergillus niger 7806F3, a fungus that showed high flocculation activity on Synechocystis cells, was selected to assess its potential for the harvest of microalgal biomass. The analyses of flocculation activity and flocculation mechanism indicated that mycelial pellets of Aspergillus niger 7806F3 exhibited high flocculation activity on Synechocystis biomass through charge neutralization mechanism, and proteins of mycelial pellets participated in the flocculation activity. The flocculation activity of strain 7806F3 on aseptic algal culture indicated that bacteria in the phycosphere can promote the flocculation effect of strain 7806F3 on algal cells. Bacterial community analysis indicated that the addition of mycelial pellets changed the bacterial community diversity in the Synechocystis phycosphere, increasing the abundance of genus Pseudomonas in the phycosphere. Finally, Pseudomonas sp. Algal4 was isolated from the Synechocystis phycosphere and confirmed with the ability to promote the flocculation activity of strain 7806F3 on Synechocystis cells. This study not only provides a method to harvest Synechocystis biomass, but also confirms the promotion effect of bacteria in phycosphere on flocculation activity, which provided a new understanding for the interaction between the algae and bacteria in the phycosphere