Pollinator gut microbiota and flower-transmitted parasites

Background/Question/Methods

Bumble bees host diverse communities of microorganisms in their gut, that may be both derived from social intra-colony transmission and transmission in the environment, e.g. on flowers. The interplay of these different microorganisms is still only poorly understood. We characterized the bacterial communities in the bumble bee gut of a range of host species in the USA and Central Europe, using high-throughput sequencing of the 16S rRNA gene, tRFLP profiles and targeted 16S sequencing of two of the main specific bacterial members of the microbiota (Snodgrassella alvi & Gilliamella apicola). We experimentally manipulated the microbiota of both Bombus terrestris and Bombus impatiens in a lab setting, and infected them with the important and florally transmitted gut parasite Crithidia bombi (Trypanosomatidae). For Bombus impatiens, we artificially created gut communities from cultured isolates of both bumble bee specific and florally transmitted gut bacteria.

Results/Conclusions

Bumble bees gut microbiota are comprised of both specific and unspecific bacterial taxa, with a strong effect of the host species on the community composition.  Experimental infections demonstate that the presence and composition of the bacterial microbiota is an important factor determining the overall infection load of Crithidia bombi. Furthermore, pathogen genotypes show a strong interaction for their infection success with the microbiota composition. The specific gut bacterium Snodgrassella alvi appears to play an important role in explaining this variation in infection success, but we also find the possibly unspecific and florally transmitted bacterium Lactobacillus kunkeei to be able to suppress infections. This suggests that bees might receive both beneficial and detrimental microorganisms when visiting flowers. We did, however, not detect differences in survival time for different bacterial microbiota and pathogen loads in our experiment, but consequences of different microbiota on the host are likely condition dependent and need to be investigated further.