I'd put on a N95 mask. Take a bucket of water with some bleach and a dish sponge. Scrub the surface of the wood down with the bleach solution. Let it dry, once dry I'd use a white vinegar spray to spray the affected wood, let it dry. If it looks good then you can either leave it or paint it with a mold encapsulating primer/paint like extreme stain block.
I wouldn't worry too much about the mold in general as warmer lower density air moves up and is pulled into the attic. Air that is already in the attic is unlikely to come into your living space. Mold isn't good for you but varies based on exposure, species and sensitivity. Mold spores exist in fresh outside air and it grows naturally outside so even fresh air will have a spore count to it. The more toxic species of mold typically have a black look - even then something of this size you should be able to self remediate.
You should get a hygrometer and find the RH of that attic it should be below 60% RH. You can do a quick check of square footage of attic and count how many air vents you have - most attic are under vented. You want soffit intake venting and ridge or high output venting. You should ensure that the insulation that is in your attic has not clogged the soffit vents.