Fig. 1.

Harvesting Nannochloropsis oceanica by bio-flocculation with Mortierella fungi. a, b Co-culture of N. oceanica (Noc) with M. elongata AG77 (a), or Morchella americana 3668S (b). Fungal mycelium collected from PDB medium was added to a log-phase Noc culture grown in flasks and both were incubated for 6 days in flasks containing f/2 medium. The red arrow indicates green aggregates formed by AG77 mycelium and attached Noc cells. c Noc cells attached to AG77 mycelium as shown by differential interference contrast (DIC) microscopy. d No obvious attachment of Noc cells on the 3668S mycelium. e Bio-flocculation efficiency for harvesting Noc cells by cocultivation with Mortierella elongata AG77, M. elongata NVP64, and M. gamsii GBAus22 in f/2 medium. The bio-flocculation efficiency was determined by the cell density of uncaptured cells compared to that of a no-fungus Noc culture control. Morchella 3668S culture was used as a negative control. The results are the average of five biological replicates and error bars indicate standard deviation. Asterisks indicate significant differences relative to the 2-h co-cultures by paired-sample Student’s t-test (*P ≤ 0.05; **P ≤ 0.01). f Measurement of Noc cell size (diameter) in the Noc culture and alga-fungus co-culture