Fungus

Can one lens catch it from another?

Or is it something with spores everywhere, and needs the right environment to grow?

I haven't got any lenses with it at the moment, but more have been passing through my hands recently, and I wouldn't want to take any risks.

Should I quarantine new acquisitions for a while?

Well, they get it from the air, but there would be a higher risk with lenses stored together if one has fungus. Just keep them dry and if one has fungus, don't keep it with the others.

Dry and well aired. Closed, damp cupboards and cases are the worst scenario.

Spores are everywhere, just leave out a piece of bread and watch the Mucor grow.

Who really rules the planet?

If it is dry enough it doesn't need to be aired. Just look at sealed museum displays, they have as little air flow as possible.

Sadly my old Super Takumar 50mm 1:1.7 has some fungus

http://www.mypentax.com/tak50_1_4.html

Enjoy . . .