Specific inhibition of Xenorhabdus hominickii, an entomopathogenic bacterium, against different types of host insect phospholipase A 2

• Published in: Journal of invertebrate pathology Vol. 149; p. 97
• Main Authors: Sadekuzzaman, Md, Kim, Yonggyun
• Format: Journal Article
• Language: English
• Published: United States 01-10-2017
• Subjects: Animals; Hemocytes - metabolism; Hemocytes - microbiology; Insect Proteins - metabolism; Larva - metabolism; Larva - microbiology; Phospholipases A2 - metabolism; Spodoptera - metabolism; Spodoptera - microbiology; Xenorhabdus - physiology; Oxindole; PLA; Xenorhabdus hominickii; Eicosanoids; Spodoptera exigua
• EISSN: 1096-0805

Phospholipase A
(PLA
) hydrolyzes ester bond of phospholipids at the sn-2 position to release free fatty acid and lysophospholipids. Some PLA
s preferentially release arachidonic acid which is subsequently oxygenated into eicosanoids to mediate immune responses in insects. Xenorhabdus hominickii is an entomopathogenic bacterium that can suppress insect immunity by inhibiting PLA
activity. However, little is known about target PLA
types inhibited by X. hominickii. Therefore, the objective of this study was to determine PLA
types in the host insect, Spodoptera exigua using specific inhibitors. All developmental stages of S. exigua possessed significant PLA
activities, with late larval stages showing relatively higher PLA
activities. In different larval tissues, hemocytes had higher PLA
activities than fat body, gut, or epidermis. Various developmental and tissue extracts exhibited differential susceptibilities to three different PLA
inhibitors. Late larva-to-adult stages were highly susceptible to all three different types of PLA
inhibitors. In contrast, extracts from egg and young larval stages were not susceptible to secretory PLA
(sPLA
) or calcium-independent cellular PLA
(iPLA
) inhibitors, although they were susceptible to a calcium-dependent cellular PLA
(cPLA
) inhibitor in a dose-dependent manner. Different tissues of fifth instars exhibited variation in susceptibility to inhibitors, with epidermal tissue being sensitive to cPLA
inhibitor only while other tissues were sensitive to all three types of inhibitors. Bacterial challenge with heat-killed X. hominickii significantly increased PLA
activity. However, live bacteria suppressed the induction of PLA
activity. An organic extract of X. hominickii-culture broth inhibited the susceptibility of S. exigua to sPLA
- and iPLA
- specific inhibitors, but not to cPLA
-specific inhibitor. Oxindole, a component of the organic extract, exhibited an inhibitory pattern similar to the organic extract. Taken together, our results indicate that S. exigua possesses different PLA
types and that X. hominickii can inhibit PLA
s susceptible to sPLA
- and iPLA
- specific inhibitors.