Sánchez Kristel F, von Elert Eric, Monell Kira, Calhoun Siobhan, Maisha Aniqa, McCreadie Paige, Duffy Meghan A
Department of Ecology and Evolutionary Biology University of Michigan Ann Arbor Michigan USA.
Department of Aquatic Chemical Ecology University of Cologne Cologne Germany.
Ecol Evol. 2024 Apr 19;14(4):e11340. doi: 10.1002/ece3.11340. eCollection 2024 Apr.
Secondary metabolites produced by primary producers have a wide range of functions as well as indirect effects outside the scope of their direct target. Research suggests that protease inhibitors produced by cyanobacteria influence grazing by herbivores and may also protect against parasites of cyanobacteria. In this study, we asked whether those same protease inhibitors produced by cyanobacteria could also influence the interactions of herbivores with their parasites. We used the - zooplankton host-fungal parasite system to address this question because it is well documented that cyanobacteria protease inhibitors suppress trypsin and chymotrypsin in the gut of , and because it is known that infects via the gut. We tested the hypothesis that gut proteases are necessary for spores to be released from their asci. We then also tested whether diets that decrease trypsin and chymotrypsin activity in the guts of lead to lower levels of infection. Our results show that chymotrypsin promotes the release of the fungal spores from their asci. Moreover, a diet that strongly inhibited chymotrypsin activity in decreased infection levels, particularly in the most susceptible clones. Our results support the growing literature that cyanobacterial diets can be beneficial to zooplankton hosts when challenged by parasites and uncover a mechanism that contributes to the protective effect of cyanobacterial diets. Specifically, we demonstrate that host chymotrypsin enzymes promote the dehiscence of spores; when cyanobacteria inhibit the activity of chymotrypsin in hosts, this most likely traps the spore inside the ascus, preventing the parasite from puncturing the gut and beginning the infection process. This study illustrates how secondary metabolites of phytoplankton can protect herbivores against their own enemies.
初级生产者产生的次生代谢产物具有广泛的功能，以及超出其直接作用范围的间接影响。研究表明，蓝藻产生的蛋白酶抑制剂会影响食草动物的摄食，还可能抵御蓝藻的寄生虫。在本研究中，我们探究了蓝藻产生的这些蛋白酶抑制剂是否也会影响食草动物与其寄生虫之间的相互作用。我们利用浮游动物宿主 - 真菌寄生虫系统来解决这个问题，因为有充分的文献记载蓝藻蛋白酶抑制剂会抑制浮游动物肠道中的胰蛋白酶和胰凝乳蛋白酶，并且已知真菌是通过肠道感染的。我们测试了一个假设，即浮游动物肠道蛋白酶对于真菌孢子从其子囊中释放是必要的。然后我们还测试了降低浮游动物肠道中胰蛋白酶和胰凝乳蛋白酶活性的饮食是否会导致感染水平降低。我们的结果表明，胰凝乳蛋白酶促进真菌孢子从其子囊中释放。此外，一种强烈抑制浮游动物胰凝乳蛋白酶活性的饮食降低了感染水平，特别是在最易感的浮游动物克隆中。我们的结果支持了越来越多的文献观点，即当受到寄生虫挑战时，蓝藻饮食对浮游动物宿主有益，并揭示了一种有助于蓝藻饮食产生保护作用的机制。具体而言，我们证明宿主的胰凝乳蛋白酶促进了真菌孢子的开裂；当蓝藻抑制宿主中胰凝乳蛋白酶的活性时，这很可能将孢子困在子囊内，阻止寄生虫穿透肠道并开始感染过程。这项研究说明了浮游植物的次生代谢产物如何保护食草动物抵御它们自己的敌人。
