• The Korean Journal of Pesticide Science
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• v.12 no.2
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• pp.184-191
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• 2008

Entomopathogenic bacteria (Xenorhabdus nematophila, X. sp. and Photorhabdus temperata subsp. temperata) isolated from entomopathogenic nematodes express potent insecticidal activity in insect hemocoel. They are also known to suppress insect immune mediation by inhibiting phospholipase $A_2$, leading to host immunosuppression. This study analyzed effects of their cultured broths on inhibiting insect immunosuppression. For this, we removed all bacterial cells using $0.2\;{\mu}m$ pore sized membrane from the bacteria-cultured broth. All three sterilized cultured media, in dose-dependent manners, significantly inhibited hemocyte-spreading behavior of 5th instar larvae of Spodoptera exigua. However, they showed differential inhibitory activities among different bacterial species, in which X. nematophila showed the most potent inhibitory activity. This immunosuppressive effect was applied to increase the pathogenicity of Bacillus thuringiensis (Bt). All three bacterial cultured broths including bacterial cells significantly potentiated Bt pathogenicity against young S. exigua larvae when each of them was orally administered in a mixture of low dose of Bt. Finally, we tested the effect of oral administration of the cultured media containing the immunosuppressive compound(s) secreted by the bacteria. The membrane-sterilized cultured broths were mixed with the low dose of Bt and then orally administered to the young S. exigua. Only the cultured medium of X. nematophila showed increase of Bt pathogenicity. These results indicated that the; cultured media of the three bacteria possessed immunosuppressive factor(s), which may act to potentiate Bt toxicity to young S. exigua larvae.

• Korean journal of applied entomology
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• v.51 no.1
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• pp.39-45
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• 2012

The entomopathogenic bacterium, $Xenorhabdus$ sp., was isolated from an entomopathogenic nematode, $Steinernema$ $monticolum$. When these bacteria were injected into the hemocoel of the diamondback moth, $Plutella$ $xylostella$, they caused significant mortality. However, the bacterium was not pathogenic when it was administered orally. This study showed that $Xenorhabdus$ sp. significantly enhanced oral pathogenicity of $Bacillus$ $thuringiensis$ (Bt) against the last instar larvae of $P.$ $xylostella$. Different ratios of culture broth of $Xenorhabdus$ sp. and Bt showed significantly different pathogenicities against $P.$ $xylostella$. In field tests, the optimal bacterial mixture significantly enhanced control efficacy against $P.$ $xylostella$ compared to Bt treatment alone. These results demonstrated that $Xenorhabdus$ sp. culture broth can be developed as a potent biopesticide by enhancing the insecticidal efficacy of Bt.

• Korean journal of applied entomology
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• v.49 no.4
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• pp.409-416
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• 2010

An entomopathogenic bacterium, Photorhabdus temperata ssp. temperata (Ptt), suppresses insect immune responses and facilitates its symbiotic nematode development in target insects. The immunosuppressive activity of Ptt enhances pathogenicity of various microbial pesticides including Bacillus thuringiensis (Bt). This study was performed to select a cheap and efficient bacterial culture medium for large scale culturing of the bacteria. Relatively cheap industrial bacterial culture media (MY and M2) were compared to two research media, Luria-Bertani (LB) and tryptic soy broth (TSB). In all tested media, a constant initial population of Ptt multiplied and reached a stationary phase at 48 h. However, more bacterial colony densities were detected in LB and TSB at the stationary phase compared to two industrial media. All bacterial culture broth gave significant synergism to Bt pathogenicity against third instars of the diamondback moth, Plutella xylostella. Production of bacterial metabolites extracted by either hexane or ethyl acetate did not show any significant difference in total mass among four culture media. Reverse phase HPLC separated the four bacterial metabolites, which were not much different in quantities among four bacterial culture broths. This study suggests that two industrial bacterial culture media can be used to economically culture Ptt in a large scale.