Microbial abundance, composition, and function in nectar are shaped by flower visitor identity

Abstract

Microbial dispersal is essential for establishment in new habitats, but the role of vector identity is poorly understood in community assembly and function. Here, we compared microbial assembly and function in floral nectar visited by legitimate pollinators (hummingbirds) and nectar robbers (carpenter bees). We assessed effects of visitation on the abundance and composition of culturable bacteria and fungi and their taxonomy and function using shotgun metagenomics and nectar chemistry. We also compared metagenome-assembled genomes (MAGs) of Acinetobacter, a common and highly abundant nectar bacterium, among visitor treatments. Visitation increased microbial abundance, but robbing resulted in 10× higher microbial abundance than pollination. Microbial communities differed among visitor treatments: robbed flowers were characterized by predominant nectar specialists within Acetobacteraceae and Metschnikowiaceae, with a concurrent loss of rare taxa, and these resulting communities harbored genes relating to osmotic stress, saccharide metabolism and specialized transporters. Gene differences were mirrored in function: robbed nectar contained a higher percentage of monosaccharides. Draft genomes of Acinetobacter revealed distinct amino acid and saccharide utilization pathways in strains isolated from robbed versus pollinated flowers. Our results suggest an unrecognized cost of nectar robbing for pollination and distinct effects of visitor type on interactions between plants and pollinators. Overall, these results suggest vector identity is an underappreciated factor structuring microbial community assembly and function.

Nectar Microbial Diversity and Changes Associated with Environmental Exposure

“…However, this is the first study to examine bacterial and fungal communities in floral nectar exposed to environmental factors and compared to nectar from flowers that opened in controlled conditions in the laboratory. From the considerable differences detected in the fungal and bacterial diversities, environmental conditions (most likely pollinator visitation) may play a considerable role in shaping the microbial community present [66,67]. Understanding the microbial diversity present in nectar is essential to assessing their effects on the nutritional value of the nectar, how they strengthen or weaken the plant-pollinator ecological mutualism, and therefore their effects on the efficacy of pollination [8,68].…”

Spatially explicit depiction of a floral epiphytic bacterial community reveals role for environmental filtering within petals

“…Nevertheless, the representation of the strains cultivated here is better, or on par with, that from other floral (Morris et al, 2020) and…”

“…For example, floral organs differ in their production of volatiles, secondary metabolites, or aqueous exudates that can support microbes (Aleklett et al, 2014; Junker & Keller, 2015; Rebolleda‐Gómez & Ashman, 2019; Steven et al, 2018). Direct evidence in support of these processes is accumulating for floral epiphytic and aqueous nectar communities (e.g., Morris et al, 2020; Rebolleda‐Gómez & Ashman, 2019; Zemenick et al, 2018). However, outside the nectar environment (e.g., Dhami et al, 2018; Vannette et al, 2020; de Vega & Herrera, 2012), no study has attempted to link microbial functional traits to floral habitat variation.…”

“…One approach to evaluating the connection between a floral habitat and microbial community functional traits is through spatially explicit isolation and culturing of microbes. This approach has accelerated our understanding of composition and functional aspects of nectar microbial communities (e.g., Herrera et al, 2010; Rering et al, 2018), but as far as we know the cultivability of the entire epiphytic community, outside nectar (Morris et al, 2020) has not been determined for any floral organ. While there is much debate over the cultivability of microbial communities including those of plants (Burch et al, 2016; Martiny, 2019; Steen et al, 2019; Yashiro et al, 2011), the diversity of the anthosphere is lower than the phyllosphere or rhizosphere (Abdelfattah et al, 2019; Rebolleda‐Gómez & Ashman, 2019; Wei & Ashman, 2018), and thus it may be possible to cultivate a larger fraction of the whole epiphytic community of a single floral organ, specifically, a petal, providing unparalleled insight into its function.…”

Natural diversity of honey bee (Apis mellifera) gut bacteriome in various climatic and seasonal states

“…Commensalibacter genus is a member of the Acetobacteraceae family, which is prevalent in the intestinal tract of many insects, mostly those that consume a sugar-rich diet 66 , for example, butterflies 67 . It was also detected in flowers, possibly originating from visiting insects 68 .…”