Yu conjectures that it may be due to their metabolites. Agrobacterium has been dubbed a "natural genetic engineer." It is endemic to soil-borne plant pathogens, and frequently causes crown gall tumors and hairy root disease.
而在生技界擁有「遺傳工程師」之稱的農桿菌，是普遍存在於土壤中的植物病原菌，常會引發冠廮腫瘤和毛狀根群。