Summary of statistical test results.

Pollen is the primary source of dietary protein for honey bees. It also includes complex polysaccharides in its outer coat, which are largely indigestible by bees but can be metabolized by bacterial species within the gut microbiota. During periods of reduced availability of floral pollen, supplemental protein sources are frequently provided to managed honey bee colonies. The crude proteins in these supplemental feeds are typically byproducts from food manufacturing processes and are rarely derived from pollen. Our experiments on the impact of different diets showed that a simplified pollen-free diet formulated to resemble the macronutrient profile of a monofloral pollen source resulted in larger microbial communities with reduced diversity, reduced evenness, and reduced levels of potentially beneficial hive-associated bacteria. Furthermore, the pollen-free diet sharply reduced the expression of genes central to honey bee development. In subsequent experiments, we showed that these shifts in gene expression may be linked to colonization by the gut microbiome. Lastly, we demonstrated that for bees inoculated with a defined gut microbiota, those raised on an artificial diet were less able to suppress infection from a bacterial pathogen than those that were fed natural pollen. Our findings demonstrate that a pollen-free diet significantly impacts the gut microbiota and gene expression of honey bees, indicating the importance of natural pollen as a primary protein source.

花粉是蜜蜂膳食蛋白质的主要来源。其外被膜含有复杂多糖，这类多糖大多无法被蜜蜂消化，却可被肠道微生物群（gut microbiota）中的细菌代谢利用。在鲜花花粉供应短缺的时段，人工饲养的蜂群常会被补充蛋白质饲料。这类补充饲料中的粗蛋白通常源自食品加工副产物，极少以花粉为原料。我们针对不同日粮的影响开展实验后发现，一种模拟单花花粉宏量营养组成的简化无花粉日粮，会使蜜蜂肠道微生物群落的规模扩大，但群落多样性、均匀度均出现下降，且潜在有益的蜂群共生细菌水平降低。此外，无花粉日粮会显著下调蜜蜂发育核心基因的表达水平。在后续实验中，我们证实此类基因表达变化可能与肠道微生物组（gut microbiome）的定植相关。最后，我们证实，对于接种了确定组成肠道微生物群落的蜜蜂个体，饲喂人工日粮的群体相较于饲喂天然花粉的群体，其抑制细菌性病原菌感染的能力显著更弱。本研究结果表明，无花粉日粮会显著影响蜜蜂的肠道微生物群与基因表达，印证了天然花粉作为蜜蜂核心蛋白质来源的重要性。