Flocculation of oleaginous green algae with Mortierella alpina fungi

•Nitrogen regime to facilitate the lipid accumulation in algae.•Incubating fungi in cell culture plates to equalize fungal biomass for each assay.•High efficient and sustainable algal harvesting with oleaginous Mortierella fungi.•Valuable algae-fungi biomass enriched in unsaturated fatty acids.•Revealing the interaction between the algal and fungal cells.