The plant is crucial: specific composition and function of the phyllosphere microbiome of indoor ornamentals

The indigenous phyllosphere microbiome was identified as a key component for plant growth and health, and for positive effects on microbial diversity within a built environment. Nevertheless, there is still limited understanding of the phyllosphere microbiota and its driving factors. To study the variability of the microbiome in relation to plant genotype and climate, we investigated 14 phylogenetically diverse plant species grown under different controlled conditions in the greenhouses of the Botanical Garden in Graz (Austria). All investigated plants showed highly specific bacterial abundances of up to 106 CFU cm-2 on their leaves. Bacterial diversity (Shannon index H’: 4.1 – 6.8) and number of putative OTUs (Chao 1: 501 – 1,097) were strongly plant species-dependent, but comprised similar dominant phyla: Firmicutes, Proteobacteria and Actinobacteria. Non-metric multidimensional scaling and BIO-ENV analysis showed a higher correlation of community composition to plant genotype rather than the ambient climatic variables. The antagonistic potential of the phyllosphere microbiome towards the plant pathogen Botrytis cinerea measured by production of antifungal volatile organic compounds (VOCs) differed in a range of 2 up to 58% of the isolates. Frequently isolated VOCs produces were represented by Bacillus ssp., Stenotrophomonas rhizophila and Kocuria ssp. Surprisingly, the applied biopesticide B. thuringiensis Bt407 was found well-established in all phyllospheres. This study indicates that indoor ornamentals feature a distinct, stable microbiota with a high proportion of antifungal VOC-producers on leaves irrespective of the indoor climate. Hence, the microbiome of phyllospheres stabilize microbial diversity indoors, and can lead to beneficial effects on human health inside buildings.