2026 Undergraduate Research Showcase

Effects of Osmotic Stress on Growth Dynamics of Bacillus amyloliquefaciens

Document Type

Student Presentation

Presentation Date

4-24-2026

Faculty Sponsor

Jaycee Fahrner and Dr. Leonora Bittleston

Abstract

Microorganisms frequently encounter environmental stress in natural and agricultural systems, where fluctuations in water availability and salinity can strongly influence survival, growth, and ecological function. Understanding how bacteria respond to osmotic stress is particularly important for plant-associated microbes, as soil environments often experience salinity exposure. These stress regimes may shape not only overall growth but also phenotypic variability and adaptive capacity within microbial populations. Bacillus amyloliquefaciens is a plant-associated bacterium commonly found in soils, within the rhizosphere, and on plant tissues, where osmotic fluctuations are common. In this study, we evaluated how osmotic stress influences key growth characteristics of B. amyloliquefaciens, including total growth, growth rate, and lag time. Cultures were exposed to a gradient of osmotic stress through the addition of sodium chloride (salt) to bacterial growth media. Salt stress treatments involved continuous exposure to salt, while pulse treatments exposed cells to short-term, high-intensity salt conditions followed by a recovery phase. Growth dynamics were measured using a plate reader and analyzed for comparison between salt stress treatments and unstressed controls. We hypothesized that increasing salt concentration would progressively decrease growth rate and maximum density while increasing lag time, with extreme concentrations (up to 500 mM NaCl) severely inhibiting or preventing growth. Surprisingly, in preliminary press-stress trials, NaCl concentrations up to 500 mM increased total optical density (OD) in B. amyloliquefaciens. However, this effect could be driven by an increase in biofilm formation at higher salt levels. While concentrations from 300 to 500 mM still showed greater OD than lower concentrations in a second experiment, lag time also increased, indicating delayed growth. By better understanding the drivers of phenotypic changes in B. amyloliquefaciens, we can improve stress-resilience in bacteria and use those properties to benefit its plant mutualists. Bacteria can protect crops against pathogens and promote plant growth in food -crops and future biofuel-producing crops. Considering our initial findings, our strain of B. amyloliquefaciens can tolerate quite salty environments, which could be relevant when planning future crop applications.

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