You’re asking a question without a complete answer, as it’s a complex system in active research, but truthfully, I only know of a couple offhandedly. Some strains of lactobacillus occupy space largely benignly, and some E. coli produce vitamin k. But mostly, they’re just eating and multiplying. Hit up Wikipedia for an abundance of specifics.
Only time I’ve seen an ethical love potion plot was a cute little comic featuring a couple looking to spice things up due to mutual boredom. They split a love potion, but neither changed their behavior. Both remained bored together, but with slight, visible smiles.