Characterization of Microbial Communities Populating the Inflorescences of Humulus lupulus L.

The aerial portion of plants (phyllosphere) harbors complex and diverse microbial communities that have been shown to influence host growth and fitness, tolerance to environmental stressors, disease susceptibility, and the productivity of economically significant crops. However, despite its reproductive importance to the host and economic value, the microbial ecology of anatomical flowers (anthosphere) remains largely uninvestigated. Here a culture-independent assessment of bacterial communities on freshly harvested and dried inflorescences of eight hop varieties (Humulus lupulus L.), using Illumina MiSeq 16S platform-based rRNA gene sequence analysis, is reported. The results reveal the hops anthosphere is dominated by a single taxonomic phylum, the Proteobacteria, where at least 60% of the sequences are attributed across two genera, Pseudomonas (Gammaproteobacteria) and Sphingomonas (Alphaproteobacteria). Chao1 diversity analysis indicated the presence of many very rare taxa across all varieties. Beta-diversity analysis resolved, from the comparison of unweighted and weighted UniFrac distances, the absence of distinct clustering between freshly harvested and dried hops or between hop varieties. The prevalence of Proteobacteria associated with hop inflorescences is consistent with other anthosphere microbiomes; however, presently the predominance of Gammaproteobacteria in the phyllosphere appears to be a distinct characteristic of the hops microbiome.