细菌调控捕食线虫真菌捕杀线虫的分子机制

发布时间：2018-05-13 22:42

本文选题：食物细菌 + 尿素　；参考：《云南大学》2015年博士论文

【摘要】：自然界中,食物细菌被认为是一类为线虫提供食物的被动牺牲品。作为线虫的食物,这类群细菌是如何生存并保持与捕食者相互动态平衡,进而维持自然生态系统中物种平衡的?这是微生物生态领域至今悬而未诀的重要科学问题。本研究揭示了这类细菌通过调控捕食线虫真菌从腐生到寄生的生活史转换-形成捕食器,帮助其捕杀线虫,使线虫从捕食者变为被捕食者,从而达到细菌、真菌和线虫三者动态平衡。本研究发现,高温灭菌的牛粪对少孢节丛孢捕食器的诱导活性降低了6倍,推测牛粪细菌在诱导过程中可能起到关键作用。检测牛粪中126株细菌,发现55株细菌能够诱导捕食器形成,其中嗜麦寡养单胞菌是诱导捕食器形态建成最有效的菌株。随后,结合柱层析、活性追踪、质谱等波谱方法确定尿素是嗜麦寡养单胞菌CD52诱导捕食器形成的活性化合物,且尿素对诱导捕食线虫真菌形成不同类型的捕食器具有广谱性。进一步检测发现,活性细菌都产生尿素,因此,尿素是调控捕食器形态建成的信号分子。精氨酸反应中,精氨酸酶裂解精氨酸生成鸟氨酸和尿素。RT-PCR分析显示精氨酸酶在活性细菌中表达,且线虫胁迫下表达量显著提高。随后,敲除CD52中精氨酸酶基因获得突变体SmAarcA, LC-MS检测SmAarcA完全不能产生尿素,并且诱导捕食器形成率降低了60%,证实细菌通过调节精氨酸酶的活性分泌尿素影响捕食器形态建成。基因组序列分析显示少孢节丛孢中存在尿素转运蛋白和脲酶基因。同位素[13C,15N2]-urea追踪发现：敲除转运蛋白Utp79基因后,突变体Ao Autp79胞内完全检测不到同位素；但是,脲酶突变体AoΔure1胞内同位素积累量显著上升。与此同时,尿素完全不能诱导突变体AoΔutp79和AoΔure1产生捕食器。因此,尿素必须转运进入真菌细胞内,经过脲酶作用诱导捕食器的形成。尿素循环中,脲酶催化尿素生成氨和二氧化碳。活性测定发现,氨可以高效诱导捕食器的形成,而二氧化碳不能,所以,氨是诱导捕食器的下游信号分子。通过研究细菌对线虫的发育、后代、寿命和食物偏好的影响,确定了产尿素细菌对线虫的生长发育没有影响,这类细菌是线虫的食物细菌。尿素作为地下信号分子可以在土壤中高效扩散,而且,与线虫共同作用时,尿素显著提高捕食器形成数量,暗示尿素与线虫协同诱导捕食器形成。分析土壤中食物细菌、线虫和捕食线虫真菌三者之间的动态关系发现,产尿素的食物细菌可以促使捕食线虫真菌捕食器显著增多,捕杀线虫的起始时间提前8h。更重要的是,捕食线虫真菌可以挽救食物细菌的群体数量,这些现象证实,食物细菌调控真菌产生更多捕食器杀死线虫。综上所述,食物细菌可以产生尿素调控捕食线虫真菌杀死其天敌线虫,从而维持自身群体的稳定,提示捕食与被捕食者之间的相互关系在维持自然界物种的平衡中起着重要的作用。
[Abstract]:In nature, food bacteria are considered as a passive victim of food for the nematode. As the food of the nematode, how does the group of bacteria survive and maintain dynamic balance with the predator, thus maintaining the balance of species in the natural ecosystem? This is an important scientific question suspended in the field of microbial ecology. The study reveals that these bacteria convert nematode fungi from saprophyte to parasitic life history - forming a predator, helping them to kill nematodes, making nematodes from predators to predators, thus achieving dynamic balance between the three species of bacteria, fungi and nematodes.
This study found that the induced activity of high temperature sterilized cow dung to oligospora trumpet predation was reduced by 6 times, and that cow dung bacteria could play a key role in the induction process. 126 strains of bacteria in cow dung were detected and 55 bacteria could induce the formation of predator. Subsequently, combined with column chromatography, activity tracing, mass spectrometry and other wave methods, urea was the active compound formed by the CD52 induced predator, and urea was broad-spectrum for different types of predatory fungi to induce nematode predatory fungi. A signal molecule morphogenetic in a food device.
In the reaction of arginine, arginase lysis of arginine produced ornithine and urea.RT-PCR analysis showed that arginine was expressed in active bacteria, and the expression amount was significantly increased under nematode stress. Then, the mutant SmAarcA was obtained by knockout of the arginase gene in CD52, and LC-MS detected that SmAarcA completely failed to produce urea and induced the formation of a predator. The rate is reduced by 60%, which confirms that bacteria regulate the formation of the preys by regulating the activity of arginase and excreting urea.
Genomic sequence analysis showed the presence of urea transporter and urease gene in the small sporospora. Isotopic [13C, 15N2]-urea traced: after knockout of transporter Utp79 gene, the mutant Ao Autp79 was completely undetected in the cytoplasm of Ao Autp79; however, the accumulation of intracellular isotopes in the urease mutant Ao Delta ure1 increased significantly. The mutants Ao Delta utp79 and Ao Delta ure1 can not be induced to produce a predator. Therefore, urea must be transported into the fungal cells to induce the formation of a predator through urease action. Urease catalyzes urea to produce ammonia and carbon dioxide in the urea cycle. Ammonia is a downstream signal molecule that induces a predator.
By studying the effects of bacteria on the development, offspring, life and food preference of nematodes, it is determined that urea producing bacteria have no effect on the growth and development of nematodes. These bacteria are the food bacteria of the nematode. Urea can spread efficiently in the soil as an underground signal molecule, and when the nematode is combined with the nematode, urea can significantly increase the formation of the predator. The dynamic relationship between the food bacteria in the soil, the nematode and the nematode trapping fungi in the soil, the dynamic relationship between the three groups of nematode and nematode fungi found that the food bacteria producing urea could increase the predation of the nematode predatory fungi. The predation of the nematode early 8h. was more important than that of the nematode predatory fungi. The number of bacteria saved in food helps to confirm that food bacteria control fungi produce more predators to kill nematodes.
In summary, food bacteria can produce urea to regulate the nematode predatory fungi to kill their natural enemy nematodes, thus maintaining the stability of their own populations, suggesting that the relationship between predators and predators plays an important role in maintaining the balance of natural species.

【学位授予单位】：云南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：S432.45;S476.1

【参考文献】