Abstract
The first step in understanding gut microbial ecology is determining the presence and potential niche breadth of associated microbes. While the core gut bacteria of adult honey bees is becoming increasingly apparent, there is very little and inconsistent information concerning symbiotic bacterial communities in honey bee larvae. The larval gut is the target of highly pathogenic bacteria and fungi, highlighting the need to understand interactions between typical larval gut flora, nutrition and disease progression. Here we show that the larval gut is colonized by a handful of bacterial groups previously described from guts of adult honey bees or other pollinators. First and second larval instars contained almost exclusively Alpha 2.2, a core Acetobacteraceae, while later instars were dominated by one of two very different Lactobacillus spp., depending on the sampled site. Royal jelly inhibition assays revealed that of seven bacteria occurring in larvae, only one Neisseriaceae and one Lactobacillus sp. were inhibited. We found both core and environmentally vectored bacteria with putatively beneficial functions. Our results suggest that early inoculation by Acetobacteraceae may be important for microbial succession in larvae. This assay is a starting point for more sophisticated in vitro models of nutrition and disease resistance in honey bee larvae.
Highlights
Insects are known to harbor microbial gut communities that provide protection from pathogens and contribute to nutrition
Species of Bacteria Found in each Site A total of 186 isolates were compared based on their 16S rRNA
Gene sequences and classified as the following bacterial phylotypes: a) Alphaproteobacteria, acid forming gram-negative bacteria; b) Betaproteobacteria belonging to family Neisseriaceae, gramnegative bacteria; c) Firmicutes, gram-positive bacteria belonging to genera Bacillus and Lactobacillus, and genus Fructobacillus formally classified in genus Leuconostoc; and d) Actinobacteria, genus Bifidobacterium, acid forming gram-positive bacteria (Fig. 1)
Summary
Insects are known to harbor microbial gut communities that provide protection from pathogens and contribute to nutrition. This is especially true for nutritionally limited organisms or those that subsist primarily on complex plant polymers [1]. Acetic acid bacteria (AAB) are associated with insects that have sugar rich diets, and have been demonstrated to interact directly with the expression of antimicrobial peptides in the gut, affect larval development time, and contribute to cognitive function and general epithelial health [6,7,8,9]. Lactobacillus spp. in both solitary and social bees are thought to protect food stores and inhibit pathogenic microbes by lowering pH levels or producing secondary metabolites [10,11,12]
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