台灣產蟲生線蟲（Steinernema abbasi）之共生菌（Xenorhabdus indica）及其代謝物對昆蟲血球及細胞株之影響

Effects of the Symbiotic Bacterium, Xenorhabdus indica, from the Entomopathogenic Nematode, Steinernema abbasi, and Its Metabolites on Insect Hemocytes and Cell Lines

蔡米皓(Mi-Hau Tsai) ； 唐立正(Li-Cheng Tang) ； 侯豐男(Roger F. Hou)

《台灣昆蟲》 31卷4期 (2011/12) Pp. 287-308

https://doi.org/10.6661/TESFE.2011019

摘要

台灣產蟲生線蟲（Steinernema abbasi）之共生菌為Xenorhabdus indica，其在體外培養下僅原生型菌（primary form）可分泌具有殺蟲活性之代謝物，對昆蟲細胞株SF21及S2會造成細胞壞死（necrosis），但對仔倉鼠腎細胞株 BHK-21則無活性。共生菌濾液在體外處理大蠟蛾（Galleria mellonella）血球，於24h後之壞死率與對照組具有顯著性差異，但以X. indica之脂多醣體（lipopolysaccharide, LPS）處理之大蠟蛾血球壞死率與對照組並無顯著差異，顯示此濾液對大蠟蛾血球具破壞性。以原生型及次生型（secondary form）濾液處理大鼠及山羊血球之試驗結果，其溶血率皆與對照組無顯著差異，顯示濾液中並無溶血性物質。去活性之原生型共生菌體對大蠟蛾幼蟲會造成嚴重麻痺進而死亡，此病徵與萃取原生型菌之LPS注入大蠟蛾幼蟲所產生的症狀相似，但對斜紋夜蛾（Spodoptera litura）幼蟲則無影響，顯示X. indica之LPS對大蠟蛾具神經毒。去活性之共生菌體對大鼠及山羊之溶血率均與對照組具顯差異性。在體內下，去活性之共生菌體對大蠟蛾及斜紋夜蛾幼蟲之血球均會引起壞死現象，惟對斜紋夜蛾較不明顯。原生型共生菌（X. indica）之LPS在in vitro下，對大蠟蛾血球之作用與對照組無顯著差異，顯示其LPS並非以破壞血球之免疫系統為主要因素。由以上結果推論，共生菌釋放到昆蟲血體腔中所分泌之LPS及某些代謝物，會抑制昆蟲免疫系統無法啟動，以致共生菌及線蟲能順利增殖，並引起敗血症，在短時間內殺死昆蟲。

關鍵字

蟲生線蟲 ； 共生菌 ； 脂多醣體 ； 血球 ； 細胞株

並列摘要

The symbiotic bacterium of the entomopathogenic nematode, Steinernema abbasi Taiwan strain, has been identified as being Xenorhabdus indica. Its cultured filtrates from the primary form were toxic to SF21 and S2 cell lines, causing cellular necrosis even after being autoclaved for 20 min, while those from the secondary form were not toxic to either of these two cell lines. In addition, the cultured filtrates of both forms were not toxic to the mammalian cell line, BHK21. In in vitro assays, the necrotic rates of Galleria mellonella hemocytes at 24 h after treatment with the cultured filtrates of symbiotic bacteria were significantly different from those of the control, whereas the rates treated with X. indica lipopolysaccharide (LPS) were similar to those of the control. These results indicate that necrosis in G. mellonella hemocytes occurs 24 h after being treated with the filtrates. Hemolytic rates of rat and goat red blood cells (RBCs) as treated with cultured filtrates from both forms of X. indica were not significantly different from those of the control, showing that the cultured filtrates did not contain hemolytic substances. Inactivated bacterial cells (primary form) caused serious paralysis in G. mellonela larvae and eventually killed the insects. This symptom was found to be similar to that of being injected with LPS extracted from the primary form. However, these inactivated bacterial cells were not effective against Spodoptera litura larvae. Therefore, it is suggested that LPS is neurotoxic to G. mellonella larvae. Hemolytic rates of rat and goat RBCs treated with inactivated bacteria (primary form) were significantly different from those of the control. In in vivo assays, the inactivated bacterial cells were capable of causing necrosis and subsequently killing the hemocytes of both the G. mellonella and S. litura larvae. They were, however, comparatively less destructive to S. litura hemocytes. In in vitro assays, LPS from X. indica (primary form) was not markedly detrimental to G. mellonella hemocytes compared with the control group, suggesting that LPS is not a major factor affecting the insect immune system. Therefore, it is speculated that LPS and certain substances when released into the insect hemocoel from symbiotic bacteria could hamper the insect's immune system, resulting in the proliferation of symbiotic bacteria and nematodes, and subsequently cause septicemia to rapidly kill the insect hosts.

並列關鍵字

Steinernema abbasi ； Xenorhabdus indica ； hemocyte ； cell line ； lipopolysaccharide