Date of Graduation

5-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor

Renee T. Threlfall

Committee Member

Luke R. Howard

Second Committee Member

Andronikos Mauromoustakos

Third Committee Member

Sun-Ok Lee

Fourth Committee Member

Mary C. Savin

Keywords

fermentation, grapes, high-throughput sequencing, microbiota, vineyard, yeast

Abstract

Microorganisms inhabiting the soil, leaves, and grapes in vineyards influence the terroir, a set of environmental factors that impact wine characteristics. Previously, the main method to identify microorganisms was to culture on different media, but a large portion (> 99%) could not be cultured and were consequently unidentified. However, the emergence of new molecular tools has enabled further study and identification of microorganisms such as indigenous vineyard microbiota. The objective of this research was to investigate the phylogenetic diversity of Arkansas vineyard and wine microbiota using high-throughput sequencing. In terms of the Arkansas vineyards, the fungal and bacterial diversity of leaf, soil, and grapes of different varieties from experimental vineyards (one with a high tunnel/covered structure) and commercial vineyards were evaluated. Overall, the fungal diversity of the vineyard grape, leaf, and soil samples was greater in 2017 compared to 2016, while the bacterial diversity was only greater for grapes and leaves. The indigenous grape and leaf microbiota varied depending on the location, grape varieties, and year, but some microorganisms, such as Methylobacterium and Sphingomonas, were identified as a core microbiota and were present in all leaf samples. The covered structure (high tunnel) impacted the grape and leaf microbiota with distinct microbiota compared to the other locations (dominant fungal genera Cladosporium in grapes and leaves). The soil microbiota was similar between the different vineyards with a prevalence of the fungi Mortierella and bacteria from the Acidobacteria phylum. Dissimilarities in soil bacterial communities were observed mainly for the microorganisms present at a small relative abundance (contributing to less than 20% of the total bacterial communities). In terms of wine, the presence and performance of mycobiota during fermentation of two grape varieties with different sulfite levels and yeast inoculations were evaluated. Indigenous juice microbiota of the two grape varieties were similar with the two most abundant fungal genera as Podosphaera and Candida with dissimilarities in fungal communities’ relative abundances. Sulfite levels and yeast impacted the mycobiota and wine composition during fermentation. The fermentation of uninoculated (spontaneous fermentation) juice varieties were dominated by Hanseniaspora and Saccharomyces genera. This research demonstrated the phylogenetic diversity of Arkansas vineyard and wine microbiota as well as the impact that microbiota can have on wine production. Objectives 1. Determine the phylogenetic diversity and taxonomic identity of the indigenous microbiota in Arkansas vineyards using high-throughput sequencing methods 2. Evaluate the phylogenetic diversity and taxonomic identity of microbiota during fermentation of Arkansas grape juice with different sulfite levels and yeast inoculations

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