The microbiota of halictid bee nests: Do wild bees use probiotics?

Background/Question/Methods

As Apis mellifera populations continue to decline, interest in the role that pathogens play in the health of pollinators is increasing.  For example, the best working hypotheses regarding colony collapse disorder center around viruses and either microsporidians or parasitic mites.  Interest in the role beneficial microbes play in pollinator health is also on the rise.  Surveys of microbes associated with the digestive tracts of A. mellifera have shown that 8 bacterial phylotypes consistently occur in A. mellifera worldwide, suggesting that these bacteria may play important roles in colony health.  Here, I present a pyrosequencing based investigation of bacterial communities associated with wild bees.  Specifically, I investigated the nest microbiota of a solitary halictid bee, Augochlora pura (Say), and a social halictid bee, Halictus ligatus (Say).  I tested the hypothesis that benevolent lactic acid bacteria that associate with A. mellifera also associate with wild bees.  I used bacterial tag-encoded FLX 454 pyrosequencing of 16S rRNA to quantify bee nest microbiota.  

Results/Conclusions

I find incredibly rich bacterial communities at the generic level in both nests, with a maximum of 87 genera and an average of 45 genera per brood cell.  UniFrac analysis shows that the microbiota associated with the developing insects cluster by species, but are more similar within species than the associated microbiota found in the pollen provisions and frass.  I find Lactobacillus and other putative mutualists in both nests.  Additionally, the H. ligatus nest microbiota is dominated by Lactobacillus, which is also present in large numbers in the A. pura nest.  Finally, to put the wild bee associated Lactobacillus into a broader phylogenetic context, I present a 16S rRNA phylogeny of the Lactobacillus sequences from my halictid nests along with a broad sampling of publicly available Lactobacillus sequences.  I find that halictid associated Lactobacillus spp. are interspersed throughout the Lactobacillus phylogeny, but that many are closely related to the probiotic Lactobacillus that associate with Apis mellifera.  These results suggest that Lactobacillus may be important in the health of developing wild bees.  Halictid associated Lactobacillus may be acting as probiotics, as Lactobacillus spp. are known to secrete lactic acid and lower the pH of their environment.  By lowering the pH of wild bee pollen provisions, Lactobacillus may be protecting wild bees from microbes that would otherwise spoil the provisions.