Pollen-associated microbiome correlates with pollution parameters and the allergenicity of pollen.

All over the world the occurrence of allergic diseases increased during the last decades causing massive health problems and thus imposing considerable economic burden on the society. One of the major causative factors are airborne pollen grains of anemochorous plants, e. g. diverse grasses and trees. Many allergenic proteins and non-allergenic adjuvant compounds of pollen are involved in the plant defense system against environmental or microbial stress. In this study we determined the microbial load of pollen obtained from timothy grass (Phleum pratense) and birch trees (Betula pendula) by isolating cultivable microbes and assessing the bacterial and fungal pattern composition on the pollen samples. Furthermore we wanted to investigate detectable correlations between pollen microbiota and parameters of air pollution or pollen allergenicity. Using terminal restricted fragment length polymorphism (tRFLP) analysis as well as uni-/multivariate statistics we showed that the bacterial diversity (Shannon/Simpson diversity indices) on birch pollen samples correlated to urbanization-related parameter (nitrogen dioxide (NO2), ozone (O3) and Urbanization Index (UI)), but not to on-site air pollution values of ammonia (NH3). The bacterial diversity on timothy grass pollen also correlated significantly to the Urbanization Index. Moreover, the microbial diversity on birch tree and timothy grass pollen samples were partly significantly correlated to the produced amount of allergen-related compounds (Bet v 1/Phl p 5, pollen-associated lipid mediators). Our results showed correlations of the microbial composition and environmental exposure parameters alongside with a different expression of allergen and pollen-associated lipid mediators. This might translate into an altered allergenicity of pollen due to environmental and microbial stress