Many pollinator species are declining due to a variety of interacting stressors including pathogens, sparking interest in understanding factors that could mitigate these outcomes. Diet can affect host-pathogen interactions by changing nutritional reserves or providing bioactive secondary chemicals. Recent work found that sunflower pollen (Helianthus annuus) dramatically reduced cell counts of the gut pathogen Crithidia bombi in bumble bee workers (Bombus impatiens), but the mechanism underlying this effect is unknown. Here we analyzed methanolic extracts of sunflower pollen by LC-MS and identified triscoumaroyl spermidines as the major secondary metabolite components, along with a flavonoid quercetin-3-O-hexoside and a quercetin-3-O-(6-O-malonyl)-hexoside. We then tested the effect of triscoumaroyl spermidine and rutin (as a proxy for quercetin glycosides) on Crithidia infection in B. impatiens, compared to buckwheat pollen (Fagopyrum esculentum) as a negative control and sunflower pollen as a positive control. In addition, we tested the effect of nine fatty acids from sunflower pollen individually and in combination using similar methods. Although sunflower pollen consistently reduced Crithidia relative to control pollen, none of the compounds we tested had significant effects. In addition, diet treatments did not affect mortality, or sucrose or pollen consumption. Thus, the mechanisms underlying the medicinal effect of sunflower are still unknown; future work could use bioactivity-guided fractionation to more efficiently target compounds of interest, and explore non-chemical mechanisms. Ultimately, identifying the mechanism underlying the effect of sunflower pollen on pathogens will open up new avenues for managing bee health.

中文翻译：

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评估向日葵花粉对大黄蜂肠道病原菌影响的化学机制。

由于包括病原体在内的多种相互作用的压力源，许多传粉媒介物种正在减少，激发了人们对理解可以减轻这些后果的因素的兴趣。饮食可以通过改变营养储备或提供具有生物活性的辅助化学物质来影响宿主与病原体的相互作用。最近的工作发现向日葵花粉（Helianthus annuus）大大减少了大黄蜂工（Bombus impatiens）中肠道病原体Crithidia bombi的细胞计数，但这种作用的机理尚不清楚。在这里，我们通过LC-MS分析了向日葵花粉的甲醇提取物，并确定了三香豆酰亚精胺是主要的次要代谢产物成分，以及类黄酮槲皮素-3 - O-己糖苷和槲皮素-3-O-（6- O-丙二酰基）-己糖苷。然后，我们测试了triscoumaroyl亚精胺和芦丁对效应（作为槲皮素糖苷的代理）短膜虫感染B.凤仙花，相比荞麦花粉（荞麦）作为阴性对照和向日葵花粉作为阳性对照。此外，我们分别测试了向日葵花粉中9种脂肪酸的作用，并使用相似的方法进行了组合。尽管向日葵花粉持续减少了拟南芥相对于对照花粉，我们测试的化合物均无显着影响。另外，饮食疗法不影响死亡率，蔗糖或花粉的消耗。因此，向日葵的药用作用机理尚不清楚。未来的工作可以使用生物活性指导的分馏来更有效地靶向目标化合物，并探索非化学机制。最终，确定向日葵花粉对病原体影响的潜在机制将为管理蜜蜂健康开辟新途径。