Fungal spores hyphae and conidiophores the spore producing structures of mold.
Fungus on roof rafters.
You must address the underlying moisture issue in order to stop the mold growth.
Painting or sealing it will not address the problem.
It is not necessary to remove all stains from wood.
Check for areas of dark discoloration staining of wood e g.
Left unattended the moisture and fungal growth will eventually degrade the roof sheathing.
That could indeed be and looks like a white fungus or mold growth on roof sheathing.
Attic mold is often caused by warm moist air from the house leaking into the attic space.
Roof leaks will often lead to a small localized area of attic mold near where the leak is occurring.
The mold will simply grow on top of and through the layer of paint.
Frankly nobody who actually knows much about mycology and mold would from looking at the white growth on a surface by naked eye assert that it is a species of aspergillus.
This causes condensation to form on the cold surfaces in the attic especially roof rafters sheathing and trusses.
If a fungus has developed along moisture deposits and water puddles on the roof any path that leads indoors will carry the malignant growth into your home.
How to remove mold from wood framing plywood sheathing tongue and groove subfloor or roof decking the object in cleaning mold from a wood surface is to remove all fungal material from the surface of the wood.
With biannual professional inspections you can identify such problems before they impact the structural integrity of your roof and the sanitation of your house.