Figure 1. Interaction between N.oceanica and M. elongata cells.

(A) Co-cultivation of M. elongata AG77 and N. oceanica (Noc) in flasks for 6 days. Green tissues indicated by the red arrow head are aggregates formed by AG77 mycelium and attached Noc cells. (B) Differential interference contrast micrographs of the green tissues shown in (A). A large number of Noc cells are trapped by AG77 mycelium. (C–F) Scanning electron microscopy images of alga-fungus interaction. (C) Noc cells stick to the fungal mycelium after 6-day co-culture. (D) Noc controls grown in f/2 medium alone have smooth surface. (E) A Noc cell adheres to an AG77 hypha by the outer surface with fibrous extensions, which were exposed after break of the original out layer. Yellow arrows indicate the residues of the out layer. (F) A Noc cell anchored to the AG77 hypha by the fibrous extensions. Red arrows indicate irregular tube-like extensions of the Noc cell wall connected to the surface of fungal cell wall.

Figure 1—figure supplement 1. Interaction between N.oceanica cells and M. elongata AG77 hyphae.

Interaction between N. oceanica (Noc) cells and M. elongata AG77 hyphae. (A) Noc controls grown in f/2 medium alone. The cells have smooth surface. (B) Noc cells attached to the fungal hypha after 6-day co-culture. The outer layer is broken, and the fibrous extensions are exposed. The algal outer extensions latch onto the rugged surface of the fungal cell wall. Arrowheads indicate broken pieces from the outer layer after co-culture with the fungi. (C) Free Noc cells co-cultivated with AG77 but not trapped by the mycelium. The Noc cells were filtered with PW200 mesh to remove the mycelium and attached algae. The algal outer layer shows partial damage, but the fibrous extensions are not exposed. (D) Noc cells incubated with heat-killed AG77 medium after 6 days, which have smooth surface similar to the Noc controls in (A).

Figure 1—figure supplement 2. N.oceanica cells were treated with different enzymes to mimic the expose of fibrous extensions after co-culture with fungi.

N. oceanica cells were treated with different enzymes to mimic the exposure of fibrous extensions after co-culture with fungi. (A) Noc cells grown in PBS buffer alone. (B) Noc cells treated with PBS + 4% hemicellulase (mixture of glycolytic enzymes such as xylanase and mananase) for 3 hr at room temperature (RT). (C) Noc cells treated with PBS + 2% driselase (mixture of carbohydrolases including laminarinase, xylanase, and cellulase) for 3 hr at RT. (D) Noc cells treated with PBS + hemicellulase and driselase for 3 hr at RT. The fibrous extensions are visible. (E and F) Noc cells treated with PBS + 1% chitinase or PBS + 1% lysing enzymes (mixture of glucanase, protease, and chitinase) for 6 hr at RT as negative controls.