Gut microbiota structure differs between honey bees in winter and summer

Lucie Kešnerová; Olivier Emery; Michaël Troilo; Joanito Liberti; Berra Erkosar; Philipp Engel

In the case of honey bees, the larger amount of food in the gut is likely to increase the 522 carrying capacity for the gut microbiota. In addition, pollen is a more nutrient-rich diet than 523 nectar, honey, or sucrose offering a larger diversity of different metabolic niches for gut 524 bacteria. Both factors are likely to contribute to the increased bacterial loads in bees fed 525 on pollen as compared to those fed on sugar water only. Recent reports in mice and fly 526 models have shown that an increase in nutritional richness, especially protein quantity, is 527 associated with an increase in overall abundance of the microbiota but a decrease in α-528 diversity [58, 59] . This is supported by our findings, because we observed an increase in 529 bacterial loads and a decrease in effective number of species in nurses and winter bees 530 that feed on pollen ( Fig. 2A and 2B) . Consistently, most of the phylotypes that increased in 531 total abundance (Lactobacillus Firm5, Lactobacillus Firm4, Bifidobacterium, Bartonella) are 532 located in the rectum, which is the last part of the hindgut where pollen accumulates until 533 bees defecate. In line with this, a previous report showed that the abundances of total However, not all changes observed in winter bees could be recapitulated in our 543 colonization experiment. For example, the differences observed in Bartonella levels 544 between foragers, nurses, and winter bees (Fig. 2E) were not observed in the experimental 545 bees that were fed with or without pollen (Fig. 3H) . Another example is Frischella. While Winter bees feed on pollen that has been stored in the hive for several weeks to months. 561 It has previously been shown that the consumption of an aged pollen-diet affects the gut 562 microbiota composition of nurses [12] . It will be important to characterize metabolic 563 differences between the pollen diet of winter and summer bees and to associate such Beside the increase of Commensalibacter and Bartonella, another intriguing characteristic 595 of the winter bee gut microbiota was the disappearance of minor, non-core community 596 members in the bee gut microbiota. We can exclude that these differences in community 597 composition are due to a community sampling bias, because nurses had similar bacterial 598 loads as winter bees, but showed the opposite trend in respect to the presence of minor 599 community members. We hypothesize that these minor community members are transient 600 colonizers that cannot persist in the bee gut environment over longer periods of time and 601 hence disappear in old winter bees. As some of these bacteria, e.g. Serratia or Klebsiella, 602 present potential pathogens of bees, there may be also mechanisms in place that increase All scripts and datasets will be deposited to Zenodo upon acceptance. For the revision 628 they can be found on: https://drive.switch.ch/index.php/s/zHsqyMOztvAr8Vu.