An interaction between two different living creatures is often mediated by a chemical substance, along with metabolic or morphological differentiation. Such phenomenon-based investigation of chemical substances sometimes leads to the discovery of a novel signaling substance associated with biological pest control, including pinpoint regulation of fundamental metabolisms. In studies on the metabolic regulation of denitrifying bacteria and phytopathogenic microorganisms, such chemicals linked to the introduction of new ideas and unique approaches for biorational pest controls are described.