Gut microbial communities of social bees

Abstract

The gut microbiota can have profound effects on hosts, but the study of these relationships in humans is challenging. The specialized gut microbial community of honey bees is similar to the mammalian microbiota, as both are mostly composed of host-adapted, facultatively anaerobic and microaerophilic bacteria. However, the microbial community of the bee gut is far simpler than the mammalian microbiota, being dominated by only nine bacterial species clusters that are specific to bees and that are transmitted through social interactions between individuals. Recent developments, which include the discovery of extensive strain-level variation, evidence of protective and nutritional functions, and reports of eco-physiological or disease-associated perturbations to the microbial community, have drawn attention to the role of the microbiota in bee health and its potential as a model for studying the ecology and evolution of gut symbionts.

Figure 1

Composition and spatial organization of bacterial communities within the honey bee gut. (A) The microbiota composition of a typical adult worker, based on an averaged community profile using 16S rRNA gene amplicons from whole guts. (B) Localization of different bacteria within the gut compartments, based on fluorescent in situ hybridization and qPCR studies.

Figure 2

Honey bee life history and associated changes in the gut microbiota. The microbiota of the worker caste (top) is best understood; studies of reproductive castes suggest their microbiota composition differs from that of workers. Naïve workers harbour no or very few bacteria and acquire the normal gut microbiota primarily though contact with faecal material, although other transmission routes may play a role as well (see Box 3). Total numbers of bacteria at any given life stage, estimated using qPCR with universal bacterial primers, vary between studies; given numbers are based on reasonable maximal estimates. Likewise, abundances of dominant species may differ among individual bees and sampling methods.

Figure 3

Metabolic activities of the core bee gut microbiota, as inferred from genomic, metagenomic, and metatranscriptomic data, and from experimentally verified activities from cultured bacterial strains. Fermenters (G. apicola, Bifidobacterium, Lactobacillus) dominate; some can break down plant polysaccharides found in pollen, such as pectin and xylan. Sugars are fermented to various end products (lactic acid, acetate, etc.), depending on the species and strain. De novo biosynthetic capabilities for these fermenters are limited. Fermentation products may be taken up and oxidized by Snodgrassella alvi for energy and carbon. Plausibly, the bee host also gains access to products of microbe-assisted carbohydrate breakdown.