Submitted to: PLoS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2014
Publication Date: 4/16/2014
Publication URL: http://handle.nal.usda.gov/10113/60003
Citation: Corby-Harris, V.L., Maes, P.W., Anderson, K.E. 2014. The microbial communities associated with honey bee (Apis mellifera) foragers. PLoS One. DOI: 10.1371/journal.pone.0095056.
Interpretive Summary: Honey bees and native pollinators are in the midst of a worldwide decline. Honey bees constantly find themselves in stressful situations, due to the rigors of transport, poor access to forage, and biocides. One potential consequence of such stressful situations is the disruption of the normal and healthy bacterial flora found in the hive and in the bee’s gut. While many studies show that this gut microbiota is constant for bees living within the hive, less is known about older foragers who regularly come into contact with the most rigorous of environmental pressures as they search for food. We used high-throughput DNA sequencing to determine what bacteria live in the forager guts, crops, and the pollen they were bringing into the colony. By combining these data with plate counts, we were able to determine that (1) the forager guts contained a core gut microbiota similar to that found in younger bees, (2) the crop is not hospitable for the growth of most bacteria, and (3) corbicular pollen communities contain a diverse community dominated by bacteria that are not found at high levels in the gut or crop. Our results provide further support for a core gut microbiota. They also suggest that the crop allows only a select group of bacteria to flourish and is best envisioned as an extension of the hive environment, containing taxa commonly found in food stores and vectored from the pollination environment.
Technical Abstract: The honey bee (Apis mellifera) is a key pollinator species undergoing drastic decline. Bees that are part of typical commercial operations are exposed to a variety of agricultural ecosystems throughout the year and a multitude of environmental variables that may affect the microbial balance of the individual and of the hive. While many recent studies support the idea of a core microbiota in the guts of younger in-hive bees, relatively little attention has focused on whether this core is present in forager bees and whether the incoming (corbicular) pollen that these foragers carry includes these core gut bacteria. Additionally, several studies hypothesize that the crop, a key interface between the pollination environment and hive food stores, contains a set of 13 lactic acid bacteria (LAB) that the forager inoculates their corbicular pollen with and that act in synergy to preserve pollen stores. Here, we used a combination of 454 based 16S rRNA gene sequencing of the microbial communities of forager guts, crops, and corbicular pollen and crop plate counts to show that (1) the forager guts contained a core gut microbiota similar to that found in younger in-hive bees, (2) the 13 LAB found in other studies is not specific to the crop, and (3) corbicular pollen communities contain a diverse community dominated by bacteria that are not found at high levels in the gut or crop. We suggest that that the crop is a highly selective environment and is best envisioned as an extension of the hive environment, containing taxa commonly found in food stores and vectored from the pollination environment.