Effect of Heat Sterilization on the Bioactivity of Antibacterial Metabolites Secreted by Xenorhabdus nematophila

Abstract

Photorhabdus luminescens and Xenorhabdus nematophila are entomopathogenic bacterial symbionts of beneficial nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae, respectively. These bacterial symbionts are known to secrete an array of toxins, enzymes and antimicrobials that kill, bioconvert and protect the insect host for optimal nematode growth and reproduction. The present study explores heat stability of antibacterial metabolites secreted by X. nematophila. Permeate of a liquid X. nematophila culture was subjected to various sterilization treatments to observe the effects of heat sterilization on antibacterial activity. Activity was measured as bacterial sensitivity which is assayed utilizing a modified-version of the Kirby-Bauer disk diffusion method. Results demonstrate that X. nematophila produces both heat-labile and heat-stabile antibacterials that are effective against different species of bacteria. Results also indicated that heat-stabile components are more active than heat-labile components. The discovery of an environmental organism that produces both heat-stabile and heat-labile antibacterials can be exploited to manufacture these compounds for potential medical applications for human and animal use.

A comparative analysis of entomoparasitic nematodes <i>Heterorhabditis bacteriophora</i> and <i>Steinernema carpocapsae</i>

“…As the bacterial population reaches stationary phase, production of secondary metabolites, in particular antimicrobials, and an unknown "food signal" is initiated. The secreted antimicrobials are speculated to be a defense mechanism used to ward off competing microbes that may cause the cadaver to putrefy [21,22]. Additionally, researchers suggest that unidentified food signals induce IJs to shed their protective sheaths and continue development to complete their life cycle [23,24].…”

Mass Production of the Beneficial Nematode Steinernema carpocapsae Using Solid State Fermentation

“…In return, the bacteria kill the insect by secreting protein toxin(s) into the hemolymph and bioconverting the insect into nutritional components for both the nematode and the bacteria [1]. The secreted antimicrobials are speculated to be a defense mechanism used to ward off competing microbes [2]. S. carpocapsae has become a center of attention for bio-ag researchers because it is safe and can kill harmful insects within 24-48 hours [3].…”