Xenorhabdus nematophila HB310, which is highly virulent for many insects, is symbiotic with Steinernema carpocapsae HB310. Toxin II was obtained using methods such as salting out and native-PAGE from the cells of X. n...Xenorhabdus nematophila HB310, which is highly virulent for many insects, is symbiotic with Steinernema carpocapsae HB310. Toxin II was obtained using methods such as salting out and native-PAGE from the cells of X. nematophila HB310. The histopathology of toxin II on H. armigera larvae was studied by dissecting an olefin slice of the midgut. The symptoms showed that the histopathology of the H. armigera midgut was similar to that of other novel midgut-active toxins such as the δ-endotoxins from Bacillus thuringiensis, as well as Tca from Photorhabdus luminescens W14. The midgut tissues of H. armigera fourth-instar larvae began to transform after the oral intake of the toxin Ⅱ over 6 h. First, the anterior region of the peritrophic membrane （PM） began to degrade followed by the elongation of the columnar cells. The epithelium decomposed gradually, and the midgut tissues were either loose or disordered. The PM disappeared after 12 h but reappeared after 72 h following transient or sublethal exposure to the toxin Ⅱ. Toxin Ⅱ also directly destroyed in vitro PMs of H. armigera.展开更多
Xenorhabdus nematophila, a Gram-negative proteobacterium belonging to the family Enterobacteriaceae and associated symbiotically with soil entomopathogenic nematodes, Steinernema carpocapsae, is pathogenic to a wide r...Xenorhabdus nematophila, a Gram-negative proteobacterium belonging to the family Enterobacteriaceae and associated symbiotically with soil entomopathogenic nematodes, Steinernema carpocapsae, is pathogenic to a wide range of insects. A protein complex with insecticidal activity was isolated from the cells ofX. nematophila HB310 strain using methods of salting out and native polyacrylamide gel electrophoresis （PAGE）. Seven polypeptides ranging 50~250 kDa were well separated from the protein complex （named Xnpt） by sodium dodecyl sulfate （SDS）-PAGE, five of which are identified as XptA2, xptC 1, XptB 1, GroEL and hypothetical protein by matrix-assisted laser desorption- time-of-flight mass spectrometry （MALDI-TOFMS）. Xnpt showed high oral virulence to larvae of diamondback moth （DBM）, Plutella xylostella L. （Lepidoptera, Plutellidae） as its median lethal concentration （LC50） against second and third instar larvae were 331.45 ng/mL and 553.59 ng/mL at 72 h, respectively. The histological analysis of Xnptfed DBM larvae showed extensive histopathological effects on the midgut. Biochemical analysis indicated that Xnpt markedly inhibited the activities of three important enzymes in the midgut. Overall, our data showed that the protein complex isolated from X. nematophila HB310 induced the antifeedant and death of insects by destroying midgut tissues and inhibiting midgut proteases activities.展开更多
An entomopathogenic bacterium, Xenorhabdus nematophila, has been known to induce significant immunosuppression of target insects by inhibiting immune-associated phospholipase A2 （PLA2）, which subsequently shuts down...An entomopathogenic bacterium, Xenorhabdus nematophila, has been known to induce significant immunosuppression of target insects by inhibiting immune-associated phospholipase A2 （PLA2）, which subsequently shuts down biosynthesis of eicosanoids that are critical in immune mediation in insects. Some metabolites originated from the bacterial culture broth have been identified and include benzylideneacetone, proline-tyrosine and acetylated phenylalanine-glycine-valine, which are known to inhibit enzyme activity of PLA2 extracted from hemocyte and fat body. This study tested their effects on digestive PLA2 of the beet armyworm, Spodoptera exigua. Young larvae fed different concentrations of the three metabolites resulted in significant adverse effects on larval development even at doses below 100 #g/mL. In particular, they induced significant reduction in digestive efficiency of ingested food. All three metabolites significantly inhibited catalytic activity of digestive PLA2 extracted from midgut lumen of the fifth instar larvae at a low micromolar range. These results suggest that the inhibitory activities of the three bacterial metabolites on digestive PLA2 of S. exigua midgut may explain some of their oral toxic effects.展开更多
文摘Xenorhabdus nematophila HB310, which is highly virulent for many insects, is symbiotic with Steinernema carpocapsae HB310. Toxin II was obtained using methods such as salting out and native-PAGE from the cells of X. nematophila HB310. The histopathology of toxin II on H. armigera larvae was studied by dissecting an olefin slice of the midgut. The symptoms showed that the histopathology of the H. armigera midgut was similar to that of other novel midgut-active toxins such as the δ-endotoxins from Bacillus thuringiensis, as well as Tca from Photorhabdus luminescens W14. The midgut tissues of H. armigera fourth-instar larvae began to transform after the oral intake of the toxin Ⅱ over 6 h. First, the anterior region of the peritrophic membrane （PM） began to degrade followed by the elongation of the columnar cells. The epithelium decomposed gradually, and the midgut tissues were either loose or disordered. The PM disappeared after 12 h but reappeared after 72 h following transient or sublethal exposure to the toxin Ⅱ. Toxin Ⅱ also directly destroyed in vitro PMs of H. armigera.
基金Acknowledgments This work was supported by the National Nature Science Foundation of China （NSFC, No. 30400296）, Natural Science Foundation of Hebei Province, China （C2006000443, C2008000277, C2010000706）
文摘Xenorhabdus nematophila, a Gram-negative proteobacterium belonging to the family Enterobacteriaceae and associated symbiotically with soil entomopathogenic nematodes, Steinernema carpocapsae, is pathogenic to a wide range of insects. A protein complex with insecticidal activity was isolated from the cells ofX. nematophila HB310 strain using methods of salting out and native polyacrylamide gel electrophoresis （PAGE）. Seven polypeptides ranging 50~250 kDa were well separated from the protein complex （named Xnpt） by sodium dodecyl sulfate （SDS）-PAGE, five of which are identified as XptA2, xptC 1, XptB 1, GroEL and hypothetical protein by matrix-assisted laser desorption- time-of-flight mass spectrometry （MALDI-TOFMS）. Xnpt showed high oral virulence to larvae of diamondback moth （DBM）, Plutella xylostella L. （Lepidoptera, Plutellidae） as its median lethal concentration （LC50） against second and third instar larvae were 331.45 ng/mL and 553.59 ng/mL at 72 h, respectively. The histological analysis of Xnptfed DBM larvae showed extensive histopathological effects on the midgut. Biochemical analysis indicated that Xnpt markedly inhibited the activities of three important enzymes in the midgut. Overall, our data showed that the protein complex isolated from X. nematophila HB310 induced the antifeedant and death of insects by destroying midgut tissues and inhibiting midgut proteases activities.
文摘An entomopathogenic bacterium, Xenorhabdus nematophila, has been known to induce significant immunosuppression of target insects by inhibiting immune-associated phospholipase A2 （PLA2）, which subsequently shuts down biosynthesis of eicosanoids that are critical in immune mediation in insects. Some metabolites originated from the bacterial culture broth have been identified and include benzylideneacetone, proline-tyrosine and acetylated phenylalanine-glycine-valine, which are known to inhibit enzyme activity of PLA2 extracted from hemocyte and fat body. This study tested their effects on digestive PLA2 of the beet armyworm, Spodoptera exigua. Young larvae fed different concentrations of the three metabolites resulted in significant adverse effects on larval development even at doses below 100 #g/mL. In particular, they induced significant reduction in digestive efficiency of ingested food. All three metabolites significantly inhibited catalytic activity of digestive PLA2 extracted from midgut lumen of the fifth instar larvae at a low micromolar range. These results suggest that the inhibitory activities of the three bacterial metabolites on digestive PLA2 of S. exigua midgut may explain some of their oral toxic effects.
