Photorhabdus: A microbial factory of insect-killing toxins

Abstract

The overuse of chemical pesticides to meet the production and productivity goals in modern agriculture is causing a number of unintended side effects and destruction of the environment. Eco-friendly pest management techniques and strategies are urgently needed. Photorhabdus spp. are Gram-negative gamma-proteobacteria of the family Enterobacteriaceae, found exclusively in symbiotic association with nematodes of the genus Heterorhabditis. Heterorhabditis nematodes are widely used as a biological control agent for insect-pests of crops. These nematodes carry the symbiont bacteria in their gut and release them in insect hemocoel upon infection of new insect host. Inside the insect hemocoel, Photorhabdus multiplies and releases a multitude of insecticidal toxins and secondary metabolites resulting in death of the insect by septicemia and toxemia. Some of these toxins are highly specific to their target species, while others are generalists. Stand-alone formulation of Photorhabdus bacteria is reported to be selling well in markets for insect management. Photorhabdus toxins are considered next to Bt toxins in their potential for use in insectpest management in agriculture.