Abstract
Glyphosate and copper-based herbicides/fungicides affect non-target organisms, and these incidental exposures can impact microbial populations. In this study, glyphosate resistance was found in the historical collection of S. cerevisiae, which was collected over the last century, but only in yeast isolated after the introduction of glyphosate. Although herbicide application was not recorded, the highest glyphosate-resistant S. cerevisiae were isolated from agricultural sites. In an effort to assess glyphosate resistance and impact on non-target microorganisms, different yeast species were harvested from 15 areas with known herbicidal histories, including an organic farm, conventional farm, remediated coal mine, suburban locations, state park, and a national forest. Yeast representing 23 genera were isolated from 237 samples of plant, soil, spontaneous fermentation, nut, flower, fruit, feces, and tree material samples. Saccharomyces, Candida, Metschnikowia, Kluyveromyces, Hanseniaspora, and Pichia were other genera commonly found across our sampled environments. Managed areas had less species diversity, and at the brewery only Saccharomyces and Pichia were isolated. A conventional farm growing RoundUp Ready™ corn had the lowest phylogenetic diversity and the highest glyphosate resistance. The mine was sprayed with multiple herbicides including a commercial formulation of glyphosate; however, the S. cerevisiae did not have elevated glyphosate resistance. In contrast to the conventional farm, the mine was exposed to glyphosate only one year prior to sample isolation. Glyphosate resistance is an example of the anthropogenic selection of nontarget organisms.
Highlights
We found that on a large scale, trees are a substrate source rich in yeast populations and consistent with prior studies that they are a preferred environment for S. cerevisiae
The majority (27) of S. cerevisiae isolates came from Coopers Rock State Park in West Virginia
Similar to previously identified agricultural isolates, yeast isolates from RoundUp ReadyTM corn on a conventional farm in Jefferson County, WV had the highest average of glyphosate resistance
Summary
While yeasts have become a commonplace model organism in laboratory experiments, research on the ecology, natural habitats, and genetic diversity of yeasts is relatively recent. As a model for evolutionary genetics studies, the Saccharomyces clade is one of the most studied clades of yeast, but the diversity within the genus has a complex history as the species in this clade readily hybridize with other species and are morphologically similar [1,2,3,4]. At least 30% of its genes have homologs within the human genome and to varying degrees, the human homologs can function in yeast [10] For this reason, yeasts are considered a model organism for a variety of experiments. The development of collections that include species beside Saccharomyces cerevisiae will help to expand insights into yeast evolution and the ability of yeast to withstand different environments [13]. This fermentation industry has domesticated yeast for certain brews and S. cerevisiae is seen throughout the brewing process for a variety of fermented beverages [7,18]
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