Abstract
Floral nectar is considered the most important reward animal-pollinated plants offer to attract pollinators. Here we explore whether honeybees, which act as pollinators, affect the composition of bacterial communities in the nectar. Nectar and honeybees were sampled from two plant species: Amygdalus communis and Citrus paradisi. To prevent the contact of nectar with pollinators, C. paradisi flowers were covered with net bags before blooming (covered flowers). Comparative analysis of bacterial communities in the nectar and on the honeybees was performed by the 454-pyrosequencing technique. No significant differences were found among bacterial communities in honeybees captured on the two different plant species. This resemblance may be due to the presence of dominant bacterial OTUs, closely related to the Arsenophonus genus. The bacterial communities of the nectar from the covered and uncovered C. paradisi flowers differed significantly; the bacterial communities on the honeybees differed significantly from those in the covered flowers’ nectar, but not from those in the uncovered flowers’ nectar. We conclude that the honeybees may introduce bacteria into the nectar and/or may be contaminated by bacteria introduced into the nectar by other sources such as other pollinators and nectar thieves.
Highlights
High sugar concentration which generates high osmotic pressure [1,2] and a nectar-related protein [3,4] have been suggested as limiting factors for microbial growth in floral nectar
Representative bacterial isolates were identified from both nectar and body surface, including the mouthparts of the honeybees captured from the two studied plant species (Table 1)
Bacterial species belonging to the Gammaproteobacteria, Actinobacteria and Bacilli classes were identified in the floral nectar
Summary
High sugar concentration which generates high osmotic pressure [1,2] and a nectar-related protein [3,4] have been suggested as limiting factors for microbial growth in floral nectar Despite these potentially restrictive factors, various microorganisms inhabit floral nectar: filamentous fungi, true yeasts, and yeastlike fungi [5,6,7,8]. Gilliam et al [9] examined the floral nectar of three different plant species and found that out of 23 samples of Citrus nectar only three contained some gram-negative unidentified bacteria. They were unable to isolate bacteria from cotton (Gossypium spp.) and prickly pear cactus (Opuntia sp.) nectar flowers. Alvarez-Perez and Herrera [12] demonstrated that culturable communities of nectar microorganisms associated with wild Mediterranean plants from Southern Spain, are nonrandom assemblages of bacterial and yeast species
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