Fungus can grow inside a lens if it has moisture being left there for a long time. However, fungus can easily be killed if they got expose to sunlight. That said, you should use your lens regularly (every week) and rest assure you shouldn't have fungus. Shoot an object a day, keep the fungus away ! hahaha
Unluckily, one of the lens my brother own has fungus in it and I have decided to give it a try to remove it.
I shall warn you DO NOT FOLLOW WHAT I WILL SHOW YOU BELOW. DO NOT ! DO IT AT YOUR OWN RISK !
This is how fungus looks like on my brother's Konica Minolta 75-300mm f4.5-5.6