"Clostridium sporogenes" colonizes the human gastrointestinal tract, but is only present in a subset of the population; in the intestine, it uses tryptophan to synthesize indole and subsequently (IPA) – a type of auxin (plant hormone) – which serves as a potent neuroprotective antioxidant within the human body and brain.IPA is an even more potent scavenger of hydroxyl radicals than melatonin.