Mini Winnies: scaled down and transparent Winogradsky columns for microscopy in microbiology education

Winogradsky columns were invented by Sergei Winogradsky in the 1880s and have commonly been used as a microbiology classroom learning tool in K-12 and collegiate education. However, they can be challenging to examine with microscopy. We scaled down Winogradsky columns into nuclear magnetic resonance (NMR) tubes and replaced the natural sediment with a transparent soil substitute toward the goal of observing the microbial growth under a bright-field microscope without column disassembly. Using this "Mini Winnie" approach, students can practice their microscopy skills while observing microbial growth inside the column after only days of incubation on the laboratory windowsill. Overall, we believe that the Mini Winnies provide a simple method for maximizing student engagement while giving them a greater understanding of how microorganisms interact in the environment.