Thermo-stability, dose effects and shelf-life of antifungal metabolite-containing supernatants produced by Xenorhabdus szentirmai

Authors: HAZIR, SELCUK - Adnan Mederes University; Shapiro Ilan, David; Bock, Clive; LEITE, LUIS - Biological Institute, Brazil

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2017
Publication Date: 2/1/2018
Citation: Hazir, S., Shapiro Ilan, D.I., Bock, C.H., Leite, L. 2018. Thermo-stability, dose effects and shelf-life of antifungal metabolite-containing supernatants produced by Xenorhabdus szentirmai. European Journal of Plant Pathology. 150(2):297-306. https://doi.org/10.1007/s10658-017-1277-7.
DOI: https://doi.org/10.1007/s10658-017-1277-7

Interpretive Summary: Certain fungi can cause harmful plant diseases that reduce the productivity of fruit or nut-bearing trees and vegetables. Environmentally friendly methods of controlling these plant diseases are needed. Metabolites (i.e., byproducts) of a certain bacteria (called Xenorhabdus szentirmaii) have been found to be suppressive to various fungi that attack plants. In this study, the shelf-life and stability of the metabolites were tested. The metabolites were found to be stable over a nine month period when stored in the freezer, refrigerator, or at room temperature. The metabolites were also found to be stable after autoclaving. These discoveries, displaying stability, will assist in the potential commercialization of the metabolites as a fungicidal agent for use in agriculture.

Technical Abstract: Xenorhabdus spp. produce secondary metabolites that are antifungal to protect nematode-infected cadavers from fungal colonization. In previous work, the concentrated, or cell-free metabolites of X. szentirmaii exhibited high toxicity against various fungal plant pathogens and showed great potential as natural bio-fungicides. In the current study, we determined 1. thermo-stability, 2. dose-response, and 3. shelf-life of antifungal metabolites of X. szentirmaii against Monilinia fructicola (cause of brown rot in stone fruit) and Glomerella cingulata (cause of antharacnose). Thermo-stability was determined by autoclaving bacterial culture broths. Bacterial culture broths were filtered (0.22 'm Millipore filter) to remove bacterial cells. Growth of phytopathogens was determined on amended potato dextrose agar (PDA) incorporating 10% of the supernatants from the autoclaved and filtered samples, respectively. Autoclaving had no impact on the antifungal activity of secondary metabolites. Samples of the autoclaved or filtrated supernatants were tested for activity on a monthly basis for 9 months under different storage conditions: activity was not altered when stored at room temperature, 4 oC or -20 oC. A dose-response study using both phytopathogens demonstrated that a greater dose of supernatant increased antifungal activity. The antifungal-metabolite containing supernatant of X. szentirmaii has potential as a bio-fungicide. These results demonstrate the metabolite(s) are thermo-stable, they have a long shelf-life and require no stabilizing formulation, even at room temperature.