| Title | Sequential Immunosuppressive Activities of Bacterial Secondary Metabolites from the Entomopahogenic Bacterium Xenorhabdus nematophila |
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| Author | Seonghyeon Eom, Youngjin Park, and Yonggyun Kim* |
| Address | Department of Bioresource Sciences, Andong National University, Andong 760-749, Republic of Korea |
| Bibliography | Journal of Microbiology, 52(2),161-168, 2014, |
| DOI | 10.1007/s12275-014-3251-9 |
| Key Words | insect immune, immunosuppression, Xenorhabdus nematophila, hemocyte, benzylideneacetone |
| Abstract | The entomopathogenic bacterium Xenorhabdus nematophila secretes at least eight bacterial metabolites that play crucial roles suppressing target insect immune responses by inhibiting eicosanoid biosynthesis. We analyzed sequential changes in bacterial metabolite production during bacterial growth and analyzed their individual immunosuppressive activities against the insect host, Spodoptera exigua. X. nematophila exhibited a typical bacterial growth pattern in both insect host and culture medium, and eight metabolites were secreted at different time points. At the early growth phase (6–12 h), Ac-FGV and PHPP were detected in significant amounts in the culture broth. At this early phase, both Ac-FGV (18 μg/ml) and oxindole (110 μg/ml) levels significantly inhibited phenoloxidase and phospholipase A2 activities in S. exigua hemolymph. At the late growth phase (12–36 h), all eight metabolites were detected at significant levels (10–140 μg/ml) in the culture broth and were sufficient to induce hemocyte toxicity. These results suggest that X. nematophila sequentially produces immunosuppressive metabolites that might sequentially and cooperatively inhibit different steps of insect immune responses. |