The Blightseeker alchemist archetype alters the bomb ability to turn it into a "payload of alchemically engineered fungal spores". The damage is reduced from 1d6 per odd level to 1d4 per odd level and adds an extra affect. I wouldn't think alchemical fungal spores would deal fire damage. It also is clearly not bludgeoning/piercing/slashing. I would think that it might be acid, but it doesn't say so. I kind of see it as something that may choke or irritate senses like a tear gas, or something that parasitically drains life, and/or causes sickness. Is this doing untyped magic damage?
"""Spore Bomb (Su): At 1st level, a blightseeker creates a special kind of alchemist bomb that delivers a payload of alchemically engineered fungal spores. These bombs infest their target with a virulent blight (see below). The blightseeker’s bombs deal 1d4 points of damage (instead of 1d6), plus 1d4 points of damage for every 2 alchemist levels beyond 1st.
A creature that takes a direct hit from a spore bomb must succeed at a Fortitude save (DC = 10 + half the blightseeker’s level + his Intelligence modifier) or suffer the associated blight effects. Creatures that take splash damage from the bomb are not affected by the blight."""