PURIFICATION OF TOXIC DETERMINANT LECITHINASE FROM XENORHABDUS SP. AND THEIR LARVICIDAL POTENTIAL

Abstract

A symbiotic bacteria Xenorhabdus sp. was isolated from Entomopathogenic nematode Steinernema sp. using Insect bait method. This resulted in primary and secondary colony production. The primary colonies were selected for the lecithinase assay. Xenorhabdus produce various Exoenzymes in which the present study
was concentrated on the exoenzyme Lecithinase which is the toxic determinant. Lecithinase activity of the bacteria was confirmed by lecithinase assay by spot inoculation of bacterial isolates on the nutrient broth supplemented with egg yolk emulsion, the opalescent zones were observed around the colonies producing
the lecithinase enzyme after 24 hrs and lecithovitellin reaction was also performed by inoculating the bacterial isolates into the egg yolk broth which resulted in the formation of opalescent suspension and flocculation of particles floating in the media. Lecithinase enzyme was partially purified using Sephadex G200 column chromatography. Protein profiling of partially purified lecithinase enzyme showed a single band at 70kDa. Larvicidal activity of lecithinase was tested on Coleopteran white grub (Phyllophaga sp).It was found that with increasing concentrations of lecithinase, there was increase in mortality of the pest and
vector. Thus this study confirms that the toxic determinant lecithinase can be used as potent larvicides for the control of insect pests of plants. The development of new strategies including naturally occurring larvicides to control white grub (Phyllophaga sp.) and it is important as the chemical larvicides may harm other soil dwelling organisms as well as humans