Biodiversity of pollen in indoor air samples can be revealed by DNA metabarcoding

Submitted by Tina on 6 October 2017.

By: Helena Korpelainen (author)

Nordic Journal of Botany: doi: 10.1111/njb.01623

Pollen can enter buildings through open windows and doors, and people track pollen indoors on their clothes and hair as well. Pollen of most plant species has some level of allergenicity but some types are particularly notorious for inducing symptoms of hay fever. Current pollen monitoring methods are microscope-based and labor-intensive. Although pollen of each taxon has its own unique set of characteristics, it is very time-consuming and sometimes impossible to comprehensively determine the taxonomic composition of pollen without molecular tools. Therefore, to increase precision in analyses on indoor pollen we collected samples from different buildings, and conducted DNA barcoding (nuclear ITS region) using next generation sequencing methods allowing efficient metabarcoding of pollen samples.


Sampling was conducted using a collector with a disposable filter attached to the tube of a vacuum cleaner (Figure 1). Multiple horizontal and vertical samples were collected from each of the five buildings included in the study. The same buildings were examined several times during a two-year period and, thus, also seasonal variation in pollen diversity was revealed. After vacuuming, the filter containing the dust was removed from the collector and placed in a plastic bag until processing, involving cutting the filter, rinsing the filter with water and emptying the content to a petri dish, where large non-biological particles were removed (Figure 2). Thereafter, the sample was exposed to grinding and DNA extraction, followed by DNA amplification and sequencing.


The results showed that good-quality sequences were obtained, and DNA barcoding allowed a comprehensive discovery of taxonomic diversity. The numbers of spermatophyte families and genera varied greatly among sampling sites and times. The total number of spermatophyte genera found during the study was 187, of which 43.9, 39.6, 7.5 and 9.1% represented wild, garden/crop and indoor house plants, and non-domestic fruit or other plant material, respectively. Comparable proportions of individual sequences equalled 77.4, 18.8, 2.7 and 1.1%, respectively. When comparing plant diversities and taxonomic composition among buildings or between seasons, no obvious pattern was detected, except for the second summer, when pollen coming from outdoors was highly dominant and the proportions of likely allergens, birch, grass, alder and mugwort pollen, were very high.


Cleaning frequency may strongly contribute to the observed biodiversity of pollen. The discovery of considerable diversities of indoor pollen in both winter and summer shows that substantial amounts of pollen produced in summer enter buildings and stay there throughout the year.