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Environmental transitions, such as the salinity divide separating marine and fresh waters, shape biodiversity over both shallow and deep timescales, opening up new niches and creating opportunities for accelerated speciation and adaptive radiation. Understanding the genetics of environmental adaptation is central to understanding how organisms colonise and subsequently diversify in new habitats. We used time‐resolved transcriptomics to contrast the hyposalinity stress responses of two diatoms. Skeletonema marinoi has deep marine ancestry but has recently invaded brackish waters. Cyclotella cryptica has deep freshwater ancestry and can withstand a much broader salinity range. Skeletonema marinoi is less adept at mitigating even mild salinity stress compared to Cyclotella cryptica, which has distinct mechanisms for rapid mitigation of hyposaline stress and long‐term growth in low salinity. We show that the cellular mechanisms underlying low salinity tolerance, which has allowed diversification across freshwater habitats worldwide, includes elements that are both conserved and variable across the diatom lineage. The balance between ancestral and lineage‐specific environmental responses in phytoplankton have shaped marine–freshwater transitions on evolutionary timescales and, on contemporary timescales, will affect which lineages survive and adapt to changing ocean conditions. 

As one of the most famous fermented drinks in the world, beer is an especially relatable topic for microbiology courses. Here, we describe a short and easily adaptable module based on the antibacterial properties of hops used in brewing. By the 15th century, beer recipes included hops (the flower of the Humulus lupulusplant) as a bittering agent and antimicrobial. By the 19th century, the highly hopped Indian Pale Ale (IPA) became popular, and a modern myth has emerged that IPAs were invented to survive long ocean voyages such as from Britain to India. With that myth in mind, we designed a hypothesis-driven microbiology lab module that tests the plausibility of this brewing myth—namely that highly hopped beers possess enough antibacterial activity to prevent spoilage, while lowly hopped beers do not. The overall design of the module is to test the antimicrobial properties of hops using petri plates containing varying concentrations of hop extract. The module includes hypothesis generation and testing related to bacterial physiology and cell envelope morphology (hops are not equally effective against Gram-positive and Gram-negative bacteria) and to mechanisms of antimicrobial resistance (as beer spoilage bacteria have repeatedly evolved hop resistance). Pre- and post-assessment showed that students made significant gains in the learning objectives for the module, which encourages critical thinking and hypothesis testing by linking microbial physiology and antimicrobial resistance to an important and topical real-world application. 

ABSTRACT Microbial fermentation is a common form of metabolism that has been exploited by humans to great benefit. Industrial fermentation currently produces a myriad of products ranging from biofuels to pharmaceuticals. About one-third of the world’s food is fermented, and the brewing of fermented beverages in particular has an ancient and storied history. Because fermentation is so intertwined with our daily lives, the topic is easily relatable to students interested in real-world applications for microbiology. Here, we describe the curriculum for a guided inquiry-based laboratory course that combines yeast molecular ecology and brewing. The rationale for the course is to compare commercial Saccharomyces cerevisiae yeast strains, which have been domesticated through thousands of generations of selection, with wild yeast, where there is growing interest in their potentially unique brewing characteristics. Because wild yeasts are so easy to isolate, identify, and characterize, this is a great opportunity to present key concepts in molecular ecology and genetics in a way that is relevant and accessible to students. We organized the course around three main modules: isolation and identification of wild yeast, phenotypic characterization of wild and commercial ale yeast strains, and scientific design of a brewing recipe and head-to-head comparison of the performance of a commercial and wild yeast strain in the brewing process. Pre- and postassessment showed that students made significant gains in the learning objectives for the course, and students enjoyed connecting microbiology to a real-world application. 

ABSTRACT All living organisms must recognize and respond to various environmental stresses throughout their lifetime. In natural environments, cells frequently encounter fluctuating concentrations of different stressors that can occur in combination or sequentially. Thus, the ability to anticipate an impending stress is likely ecologically relevant. One possible mechanism for anticipating future stress is acquired stress resistance, where cells preexposed to a mild sublethal dose of stress gain the ability to survive an otherwise lethal dose of stress. We have been leveraging wild strains of Saccharomyces cerevisiae to investigate natural variation in the yeast ethanol stress response and its role in acquired stress resistance. Here, we report that a wild vineyard isolate possesses ethanol-induced cross protection against severe concentrations of salt. Because this phenotype correlates with ethanol-dependent induction of the ENA genes, which encode sodium efflux pumps already associated with salt resistance, we hypothesized that variation in ENA expression was responsible for differences in acquired salt tolerance across strains. Surprisingly, we found that the ENA genes were completely dispensable for ethanol-induced survival of high salt concentrations in the wild vineyard strain. Instead, the ENA genes were necessary for the ability to resume growth on high concentrations of salt following a mild ethanol pretreatment. Surprisingly, this growth acclimation phenotype was also shared by the lab yeast strain despite lack of ENA induction under this condition. This study underscores that cross protection can affect both viability and growth through distinct mechanisms, both of which likely confer fitness effects that are ecologically relevant. IMPORTANCE Microbes in nature frequently experience “boom or bust” cycles of environmental stress. Thus, microbes that can anticipate the onset of stress would have an advantage. One way that microbes anticipate future stress is through acquired stress resistance, where cells exposed to a mild dose of one stress gain the ability to survive an otherwise lethal dose of a subsequent stress. In the budding yeast Saccharomyces cerevisiae , certain stressors can cross protect against high salt concentrations, though the mechanisms governing this acquired stress resistance are not well understood. In this study, we took advantage of wild yeast strains to understand the mechanism underlying ethanol-induced cross protection against high salt concentrations. We found that mild ethanol stress allows cells to resume growth on high salt, which involves a novel role for a well-studied salt transporter. Overall, this discovery highlights how leveraging natural variation can provide new insights into well-studied stress defense mechanisms.