Is bacterial microbiome from the Polemonium caeruleum L. (Polemoniaceae) nectar geographically variable?

Abstract

Floral nectar is one of the key rewards in the mutualistic interactions between plants and pollinators. However, there is a growing amount of evidence that shows that another group of organisms may be involved in the pollination process, namely the microorganisms, which often inhabit floral nectar. However, little is known about the function and taxonomic diversity of microorganisms inhabiting the nectar of plants. Bacterial communities inhabiting nectar of a rare plant species, Polemonium caeruleum, in one artificial and two natural populations in Poland were analyzed using a metagenomic approach. Polemonium caeruleum is a boreal plant species, and requires appropriate pollinator services for seed production. The reproductive system of this plant may vary between individuals and populations (mixed-mating), as well as with insect visitor assemblages. We considered that nectar-dwelling bacteria of P. caeruleum might affect the insects visiting the plant’s flowers, which in turn can result in changes in the plant’s phenotype and its reproductive system. Bacterial diversity in nectar samples was surveyed using culture-independent 16S rRNA gene amplicon sequencing (MiSeq, Illumina). We found that bacterial communities inhabiting the nectar of P. caeruleum differed between populations, although those differences were mostly quantitative. Many of the identified bacterial genera have been found previously in nectar of other plant species, or in the guts of insect visitors, and are described as tolerant of high sugar concentrations and catalase positive (which allows bacteria to survive in the presence of hydrogen peroxide).