The effect of social reversion on the honey bee (Apis mellifera) hindgut microbiota

The honey bee (Apis mellifera) gut microbiome is integral for individual and colony-level health. A healthy gut microbiome is tied to central metabolism, provides protection from pathogens, aids in detoxification, and primes the immune system. Among the worker caste, age-based polytheism dictates the division of labor and is also integral to colony success. Independent of age, the honey bee worker can assume various physiological/behavioral roles based on colony needs. We investigated the disruption of worker age demographics on the ileum and rectum (hindgut) microbiomes, specifically, we forced foragers to revert to nursing; a task associated with youthful physiology. We hypothesized that the repeated consumption of pollen would result in oxidative stress and alterations to the microbiota. We found that the core hindgut microbiome remained relatively stable, with the exception of two putative opportunistic bacteria that differed by treatment. Associated with increased expression of prophenoloxidase (PPO) in reverted foragers, we observed the formation of diverticula in the midgut suggesting a loss of gut integrity. Collectively, our results suggest stability of the hindgut microbiome, but senescence of the midgut with reversion phenotypes becoming susceptible to septicemia.

西方蜜蜂（Apis mellifera）的肠道微生物组（gut microbiome）对其个体及蜂群整体健康至关重要。健康的肠道微生物组与核心代谢紧密关联，可抵御病原体侵袭、辅助机体解毒并激活免疫系统。在工蜂品级（worker caste）中，年龄多型性（age-based polytheism）主导劳动分工模式，这同样是蜂群成功存续的核心要素。即便不考虑年龄因素，工蜂也可根据蜂群需求承担多种不同的生理与行为角色。本研究探究了工蜂年龄分布变化对回肠（ileum）、直肠（rectum，即后肠hindgut）微生物组的影响：我们通过实验迫使采集蜂（foragers）恢复哺育行为——该任务与年轻工蜂的生理特征高度相关。我们提出假说：反复摄入花粉会引发氧化应激，并导致微生物组结构发生改变。研究结果显示，核心后肠微生物组整体保持相对稳定，仅两种推定的机会致病菌在不同处理组间存在显著差异。伴随着恢复哺育状态的采集蜂体内酚氧化酶原（prophenoloxidase, PPO）表达量上调，我们观察到其中肠（midgut）出现憩室（diverticula）结构，这表明肠道完整性遭到破坏。综合来看，本研究结果表明：后肠微生物组保持稳定，但中肠出现衰老现象，恢复哺育表型的工蜂更易罹患败血症（septicemia）。