Development of a High Efficient ��Dual Bt-Plus�� Insecticide Using a Primary Form of an Entomopathogenic Bacterium, Xenorhabdus nematophila

Abstract

A phase variation has been reported in an entomopathogenic bacterium, Xenorhabdus nematophila. Compared with a wild-type primary form, a secondary form usually loses several physiological and biochemical characters. This study showed that the phase variation of X. nematophila caused a significant alteration in its immunosuppressive activity and subsequent entomopathogenicity. A secondary form of X. nematophila was detected in laboratory colonies and exhibited significant differences in dye absorption and entomopathogenicity. In addition, the secondary form was different in its production of eicosanoid-biosynthesis inhibitors (EBIs) compared with the primary form of X. nematophila. Production of oxindole and phydroxypropionic acid was significantly reduced in the culture broth of the secondary form of X. nematophila. The reduced EBI production resulted in significant suppression in the inhibitory effects on cellular nodule formation and phenoloxidase activity. Culture broth of the primary form of X. nematophila enhanced the pathogenicity of Bacillus thuringiensis ( Bt) significantly more than the culture broth of the secondary form. Furthermore, this study developed a highly efficient "Dual Bt-Plus" to control both lepidopteran insect pests Plutella xylostella and Spodoptera exigua, by mixing two effective Bt strains along with the addition of potent bacterial metabolites or 100-fold concentrated X. nematophila culture broth.

Immunosuppressive Activities of Novel PLA2 Inhibitors from Xenorhabdus hominickii, an Entomopathogenic Bacterium

“…Different immune-associated genes including antimicrobial peptides, serine proteases, and specific immune-associated Repat family genes in S. exigua are upregulated upon Bt infection [56]. Immunosuppression of S. exigua leads to enhanced Bt pathogenicity [57]. These results suggest that the eight PLA 2 inhibitors identified in this study might have potential as novel insecticides.…”

A novel tumor-targeting strain of Xenorhabdus stockiae exhibits potent biological activities

“…Additionally, Xenorhabdus possesses significant pathogenic activity against some important insect pests of commercial crops, such as lepidopteran, dipteran, and coleopteran, and is considered a neotype biological insecticide after B. thuringiensis (Burnell and Stock, 2000;Chattopadhyay et al, 2004;Georgis et al, 2006). A highefficiency "Bt-Plus" insecticide has been reported to Frontiers in Bioengineering and Biotechnology frontiersin.org enhance the insecticidal activity of B. thuringiensis by mixing it with broth cultures of the X. nematophila primary form, which suppresses target insect immunity (Eom et al, 2014).…”

Integrated Biological Control Using a Mixture of Two Entomopathogenic Bacteria, Bacillus thuringiensis and Xenorhabdus hominickii, against Spodoptera exigua and Other Congeners

“…The culture broth was then freeze-dried, in which 1 L culture broth yielded around 3 g of dried powder (called Xh extract (XhE)). The sources of the four Bt subspecies of B. thuringiensis kurstaki , B. thuringiensis aizawai (BtA), B. thuringiensis israelensis (BtI), and B. thuringiensis tenebrionis (BtT) were previously described [ 35 ]. The Bt subspecies were cultured in TSB under the same conditions as described above.…”