S. J. BRITTON (1), M. E. Allen (2), A. J. Piefer (2), P. T. Benziger (2), J. M. Balnis (2);
(1) Duvel Moortgat USA, Cooperstown, NY, U.S.A.; (2) Hartwick College, Oneonta, NY, U.S.A.
The female inflorescence of the common hop (Humulus lupulus) is a necessary ingredient that provides distinctive aromatics, bitterness, and antiseptic properties to beer. Although substantial research has been conducted on the antiseptic properties of hops, almost no research exists on the natural microbial communities that populate this perennial herbaceous vine. High-throughput DNA sequencing was conducted on samples from hop plants to characterize the microbial community of cones and leaves, and from the soils located at the base of mature plants. Samples were obtained aseptically from hops vines in September 2014 and stored at –80°C until DNA extraction. Microbial genomic DNA was extracted directly from each soil sample (n = 8), and the microorganisms removed from the surfaces of cone (n = 9) and leaf (n = 5) samples by sonication. The V3 and V4 regions of 16S rRNA genes were PCR amplified into single amplicons of approximately 460 bp, which were sequenced with an Illumina MiSeq. A genus-level hierarchical classification grouped samples into two distinct clusters, one representing the microbiomes of cones and leaves and the second the microbiomes of soils. Shannon diversity indexes for cone and leaf samples were mostly lower than for soil samples. Cone and leaf microbiomes were dominated numerically by the genera Sphingomonas (phylum Proteobacteria), Calothrix (phylum Cyanobacteria), and Pseudomonas (phylum Proteobacteria). In most samples these genera represented 50% or more of the sequences yet none of these appeared in soils. Soils also differed in that the most common genera rarely accounted for more than 20% of all sequences. The most common genera in soils included Megasphaera (phylum Firmicutes), Pedosphaera (phylum Verrucomicrobia), and three from the phylum Proteobacteria: Azospirillum, Chondromyces, and Rhodoplanes. At the conclusion of this study we elucidate the microbial communities associated with H. lupulus, a crop of significant importance to the brewing community, and reveal potential agents of contamination resulting from the post-boil addition of hops.
Scott J. Britton holds an M.S. degree and is the US Quality Group manager for Duvel Moortgat USA and adjunct instructor of biology at Utica College, Utica, NY. He completed his graduate work in biotechnology at Johns Hopkins University (Baltimore, MD).