DI is optimized for digital (coatings, etc). It is still a full frame lens (the Tamron LD Di 70-300) though. Fungus has two forms that you'll see. One will look like a dark spot with tentacles growing from it, kind of like the spider webbing on a thick piece of broken glass. You may Also see what appears to be a fine cotton like substance that looks exactly Like spider webbing but more loosely assembled. Hold the lens up to a light source and view through from the other end (with the aperture opened all the way). Do so from both ends. If you are seeing what appear to be white lines on the surface of the glass you are most likely looking at cleaning marks (very light scratches in the outer coating). A few or even many aren't too harmful but if the lens is covered with them, it will affect things like contrast. Many Older lenses (mostly predating SLR lenses) have this problem because the coatings were more delicate, IF they were coated at all. If you Really want to scare yourself, shine a flashlight through the lens and look at all the dust inside. If you determine the lens has no fungus and decide to keep the lens, just enjoy it.
By the way. You have a dirty sensor as shown in your pic of the clouds. Towards the center (the U shaped hair) of the photo. If you don't already own one, you next investment is a Rocket Blower.