ABSTRACTThe entomopathogenic bacteriaXenorhabdus nematophilaandPhotorhabdus temperatasubsp.temperatasuppress insect immune responses by inhibiting the catalytic activity of phospholipase A2(PLA2), which results in preventing biosynthesis of immune-mediating eicosanoids. This study identified PLA2inhibitors derived from culture broths of these two bacteria. BothX. nematophilaandP. temperatasubsp.temperataculture broths possessed significant PLA2-inhibitory activities. Fractionation of these bacterial metabolites in the culture broths using organic solvent and subsequent chromatography purified seven potent PLA2inhibitors, three of which (benzylideneacetone [BZA], proline-tyrosine [PY], and acetylated phenylalanine-glycine-valine [FGV]) were reported in a previous study. Four other compounds (indole, oxindole,cis-cyclo-PY, andp-hydroxyphenyl propionic acid) were identified and shown to significantly inhibit PLA2.X. nematophilaculture broth contained these seven compounds, whileP. temperatasubsp.temperataculture broth contained three compounds (BZA, acetylated FGV, andcis-cyclo-PY). BZA was detected in the largest amount among these PLA2compounds in both bacterial culture broths. All seven bacterial metabolites also showed significant inhibitory activities against immune responses, such as phenoloxidase activity and hemocytic nodulation; BZA was the most potent. Finally, this study characterized these seven compounds for their insecticidal activities against the diamondback moth,Plutella xylostella. Even though these compounds showed relatively low toxicities to larvae, they significantly enhanced the pathogenicity ofBacillus thuringiensis. This study reports bacterial-origin PLA2inhibitors, which would be applicable for developing novel insecticides.
Phototemtide A, a Cyclic Lipopeptide Heterologously Expressed from
Photorhabdus temperata
Meg1, Shows Selective Antiprotozoal Activity
