Wild bees and their nests host Paenibacillus bacteria with functional potential of avail

Background

In previous studies, the gram-positive firmicute genus Paenibacillus was found with significant abundances in nests of wild solitary bees. Paenibacillus larvae is well-known for beekeepers as a severe pathogen causing the fatal honey bee disease American foulbrood, and other members of the genus are either secondary invaders of European foulbrood or considered a threat to honey bees. We thus investigated whether Paenibacillus is a common bacterium associated with various wild bees and hence poses a latent threat to honey bees visiting the same flowers.

Results

We collected 202 samples from 82 individuals or nests of 13 bee species at the same location and screened each for Paenibacillus using high-throughput sequencing-based 16S metabarcoding. We then isolated the identified strain Paenibacillus MBD-MB06 from a solitary bee nest and sequenced its genome. We did find conserved toxin genes and such encoding for chitin-binding proteins, yet none specifically related to foulbrood virulence or chitinases. Phylogenomic analysis revealed a closer relationship to strains of root-associated Paenibacillus rather than strains causing foulbrood or other accompanying diseases. We found anti-microbial evidence within the genome, confirmed by experimental bioassays with strong growth inhibition of selected fungi as well as gram-positive and gram-negative bacteria.

Conclusions

The isolated wild bee associate Paenibacillus MBD-MB06 is a common, but irregularly occurring part of wild bee microbiomes, present on adult body surfaces and guts and within nests especially in megachilids. It was phylogenetically and functionally distinct from harmful members causing honey bee colony diseases, although it shared few conserved proteins putatively toxic to insects that might indicate ancestral predisposition for the evolution of insect pathogens within the group. By contrast, our strain showed anti-microbial capabilities and the genome further indicates abilities for chitin-binding and biofilm-forming, suggesting it is likely a useful associate to avoid fungal penetration of the bee cuticula and a beneficial inhabitant of nests to repress fungal threats in humid and nutrient-rich environments of wild bee nests.

Full Text: https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-018-0614-1
by: Alexander Keller, Annette Brandel, Mira C. Becker, Rebecca Balles, Usama Ramadan Abdelmohsen, Markus J. Ankenbrand and Wiebke Sickel

Bacterial community structure and succession in nests of two megachilid bee genera

Studies on honeybees have revealed bacterial taxa which adopt key functions in the hive, in terms of nutrient uptake and immune responses. Despite solitary bees providing invaluable ecological services, the contribution of their microbial communities to larval health and the development and fitness of adults is mainly unknown. To address this gap, we conducted a 16S rDNA meta-barcoding study including larvae and stored pollen in nest chambers from two different megachilid solitary bee genera. We tested how host taxonomy, environmental context and the developmental stage of larvae determined richness and composition of associated bacterial communities. A total of 198 specimens from Osmia bicornis, Osmia caerulescens, Megachile rotundataandMegachile versicolor nests were investigated. Solitary bee bacterial microbiota in the nesting environment were mostly homogeneous within species, and not significantly affected by landscape. For each bee species, we identified bacterial taxa that showed consistent occurrence in the larvae and stored pollen. For the pollen provision, we also described a community shift with progressing larval development, suggesting a reduction of imported floral bacteria.

by: Anna Voulgari-Kokota, Gudrun Grimmer, Ingolf Steffan-Dewenter, Alexander Keller