Advances in molecular biology of mutualism in symbiotic bacteria associated with entomopathogenic nematode

Current knowledge of mutualism between entomopathogenic nematodes,Xenorhabdus and Photorhabdus bacteria,and the molecular mechanisms involved in this,are reviewed.Xenorhabdus and Photorhabdus,members of the bacterial family Enterobacteriaceae,are highly virulent to a wide range of insect pests but have a mutualistic association with the entomopathogenic nematodes Steinernema and Heterorhabditis.These bacteria therefore engage in both pathogenic interaction with insect hosts and mutualistic interaction with nematode hosts during their life cycle.The bacteria provide four essential functions for their nematode hosts:(1) production of food signals to induce development of arrested,non-feeding infective nematode juveniles(IJs),(2) production of nutrients to facilitate nematode growth and development,(3) colonization and growth within IJ nematodes,(4) production of nematicidal toxin capable of killing non-symbiotic nematodes.