Interactions between fungi and bacteria influence microbial community structure in the Megachile rotundata larval gut

Abstract

Recent declines in bee populations coupled with advances in DNAsequencing technology have sparked a renaissance in studies of bee-associated microbes. Megachile rotundata is an important field crop pollinator, but is stricken by chalkbrood, a disease caused by the fungus Ascosphaera aggregata. To test the hypothesis that some gut microbes directly or indirectly affect the growth of others, we applied four treatments to the pollen provisions of M. rotundata eggs and young larvae: antibacterials, antifungals, A. aggregata spores and a no-treatment control. We allowed the larvae to develop, and then used 454 pyrosequencing and quantitative PCR (for A. aggregata) to investigate fungal and bacterial communities in the larval gut. Antifungals lowered A. aggregata abundance but increased the diversity of surviving fungi. This suggests that A. aggregata inhibits the growth of other fungi in the gut through chemical or competitive interaction. Bacterial richness decreased under the antifungal treatment, suggesting that changes in the fungal community caused changes in the bacterial community. We found no evidence that bacteria affect fungal communities. Lactobacillus kunkeei clade bacteria were common members of the larval gut microbiota and exhibited antibiotic resistance. Further research is needed to determine the effect of gut microbes on M. rotundata health.

Characterization of pollen and bacterial community composition in brood provisions of a small carpenter bee

“…kunkeei (McFrederick et al . , , b) was the most proportionally abundant bacterium across all brood provisions. Lactobacillus sp.…”

“…kunkeei , which we have previously reported associated with multiple halictid and megachilid bees and their brood provisions (McFrederick et al . , , b). The endosymbionts Wolbachia and Sodalis were also found in many brood provisions (Fig.…”

“…), especially bacteria that have either been found on flowers or have relatives that are found on flowers (McFrederick et al . , , b). In sweat bees in the genus Megalopta, these bacteria appear to be transmitted at flowers, and introduced into bee nests when the mother or workers place pollen and nectar into brood cells (=sealed chamber within which a single juvenile bee develops) (McFrederick et al .…”

Context‐dependent vertical transmission shapes strong endosymbiont community structure in the pea aphid, Acyrthosiphon pisum

“…Host ecology and phylogeny do not explain all variability across microbiomes, however. Indeed, patterns of symbiont exclusion and co‐occurrence (Arumugam et al., ; Wang et al., ) suggest that within‐host–microbe interactions (McFrederick, Mueller, & James, ) may further govern the structure of resident symbiont communities.…”

Social behavior in bees influences the abundance ofSodalis(Enterobacteriaceae) symbionts

“…Many social (but not solitary) halictids have been observed repeatedly opening, cleaning, and inspecting the cells of their developing offspring (8,54), and it is abundantly clear that there is a greater extent of interactions among adults in social versus solitary halictid nests. However, both social and solitary halictids are mass provisioners, collecting and provisioning the full pollen supplies to their developing offspring at the time of oviposition (8) and, in addition, bacteria can easily colonize host bees from the environment (21,(55)(56)(57). These latter modes of transmission now appear to be much more influential than we initially predicted.…”