Microbes in the naturel settings coexist and interact with distinct microbial species in cooperative or competitive manners. Although it has been well recognized that such interspecies interactions were important as determinants of microbial behaviors in nature, variety of interactions and the relevant mechanisms remain largely unknown. We are analyzing the microbial behaviors (e.g. physiology, gene expression profiles, adaptive evolution) in mixed culture systems to elucidate effects and underlying mechanisms of various interspecies interactions and exploring novel microbial functions which are induced by the interactions. Especially, we are focusing on the interspecies interactions involving drug resistance of pathogen and community and evolutionary dynamics within prey-predator systems, trying to obtain fundamental knowledge for the development of novel therapeutic strategy and the deeper understanding of the nature of biological community.