Modification of Medium Composition for Enhancing the Production of Antifungal Activity from Xenorhabdus stockiae PB09 by Using Response Surface Methodology.

Chirayu Sa-Uth,Paweena Rattanasena,Angsumarn Chandrapatya,Prapassorn Bussaman

doi:10.1155/2018/3965851

Abstract

Xenorhabdus stockiae PB09 bacterium has been shown to exhibit antifungal activity against several plant pathogens. To improve its efficacy, the optimization of the nutritional components in culture media was performed. The medium components that have significant effects on antifungal activity of X. stockiae PB09 were initially identified using a fractional factorial design. Response surface methodology and central composite design were then used to create a model for optimizing the levels of carbon, nitrogen, and mineral sources that maximize antifungal activity of X. stockiae PB09. After that, the suitable carbon, nitrogen, and mineral sources were selected and adjusted by the second-order polynomial regression model, which predicted that 98.62% of antifungal activity could be obtained when the medium contained sucrose, yeast extract, NaCl, and K2HPO4 at 3.24, 23.71, 5.46, and 2.73 g/L, respectively. Laboratory verification of this recipe resulted in the antifungal activity at 97.95% in the shake flask experiment after 48-hour cultivation, which was significantly 27.22% higher than that obtained by using the TSB medium. In addition, X. stockiae PB09 cultured in the verified recipe by using 5 L fermenter could effectively inhibit the mycelial growth of Phytophthora sp., Rhizoctonia solani, Pythium sp., and Fusarium oxysporum. This study demonstrated that the RSM and CCD were shown to be valuable tools for optimizing the culture medium that maximize the antifungal activity of X. stockiae PB09.

Highlights

Entomopathogenic nematodes of the genera Steinernema are effective biological control agents for a wide range of agricultural pests [1]
Xenorhabdus stockiae PB09 isolate was derived from the infective juveniles (IJs) of Steinernema siamkayai Stock, Somsook, and Reid, which was obtained from the Department of Agriculture, Ministry of Agriculture and Cooperatives, ailand, using the method described by Kaya and Stock [25]
Effects of Different Media on Biomass and Antifungal Activity of X. stockiae PB09. e effects of three different media, tryptone soy broth (TSB), Luria Bertani broth (LB), and YSG, on biomass and antifungal activity of X. stockiae PB09 cells after cultivation by using shake flasks at different periods of time are shown in Table 5. e maximum dry cell weight was found when the bacteria were cultured for 48 h on TSB (11.90 g/L). e cell-free supernatant of X. stockiae PB09 cultivated by using TSB medium for 48 h exhibited the highest inhibitory activity against the mycelial growth of Phytophthora sp. (70.73%)

Summary

Introduction

Entomopathogenic nematodes of the genera Steinernema are effective biological control agents for a wide range of agricultural pests [1]. When Steinernema nematodes infest the insect hosts, they release their symbiotic bacteria Xenorhabdus spp., into hosts’ haemocoels. En, Xenorhabdus spp. bacteria cause septicemia and release digestive enzymes that kill and degrade the host within 48 h [1]. A variety of metabolites produced by Xenorhabdus spp. can destroy the insect’s immune system [2] and inhibit the fungal and bacterial competitors [3, 4]. Xenorhabdus spp. has been used as a biological control agent against Luciaphorus perniciosus Rack, the mushroom mite that is endemic in ailand [8,9,10]. Xenorhabdus spp. has been used as a biological control agent against Luciaphorus perniciosus Rack, the mushroom mite that is endemic in ailand [8,9,10]. e antimicrobial compounds produced by Xenorhabdus spp. are known to inhibit several fungal plant pathogens [1, 3, 4, 11, 12], and these compounds have been isolated and identified, including xenorhabdins [13], xenocoumacin [14], nematophin [15], and indole derivatives [16].

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Results

Conclusion