Bacterial communities associated with honey bee pollen collection and storage

Background/Question/Methods

The honey bee (Apis mellifera) is a key pollinator species experiencing drastic decline worldwide. As part of a commercial operation, bee colonies are exposed to a variety of agricultural ecosystems throughout the year and a multitude of environmental variables that may affect the microbial balance of individuals and the hive. While many recent studies support the idea of a core microbiota in the guts of younger in-hive bees, it is unknown whether this core is present in forager bees or the pollen they carry back to the hive. The foregut (crop) represents a key interface between the pollination environment and hive food stores, and the present paradigm suggests that the bacteria that occupy this portion of the alimentary tract are critical for the preservation of pollen stores. Here, we used 454 based 16S rRNA gene sequencing of the microbial communities of forager guts, crops, corbicular pollen, stored pollen, and flowers to determine the bacterial communities involved in pollination and pollen storage.

Results/Conclusions

We found that (1) despite a very different diet, the forager guts contained a core microbiota similar to that found in younger in-hive bees,  (2) corbicular pollen contains a diverse community dominated by hive-specific, environmental or phyllosphere bacteria that were not prevalent in the gut or crop, and (3) the 13 LAB found in culture-based studies are not specific to the crop but are a small subset of midgut or hindgut specific bacteria identified in many recent 454 amplicon-based studies. The crop was dominated by Lactobacillus kunkeei, and Alpha 2.2 (Acetobacteraceae), highly osmotolerant and acid resistant bacteria with close relatives occupying nectar, and found at high frequency in stored pollen and honey. Crop taxa at low abundance include core hindgut bacteria in transit to their primary niche, and potential pathogens or food spoilage organisms likely vectored from the pollination environment. We conclude that the crop is a highly selective microbial environment that functions in both decontamination and inoculation.