Using the Winogradsky Column In a Lab Course

When most of us hear the term “biodiversity,” we think of tropical rainforests and coral reefs. In fact, perhaps the most critical biodiversity exists right under our feet: in the microbial world that inhabits our soil and surface waters. The earliest forms of life — microbes — evolved 3.5 billion years ago, and their descendants still shape the ecosystems and evolution of life on Earth.

When I taught biology for majors at a community college and we covered evolution, we started from the ground up with microbes such as bacteria. Although people think of bacteria as “germs” and causes of disease, only a small proportion of known bacterial species actually cause disease or can even live at human body temperature. The vast majority of bacteria and archaea participate in nutrient cycling or are food for other species, essential to food webs. These humble microbes are in fact critical to the cycling of nutrients — carbon, nitrogen, and sulfur in particular — throughout the planet, also known as the biogeochemical cycles of the Earth. To investigate microbes, 19th century microbiologist Sergei Winogradsky developed a “column” method, now known as the Winogradsky column, to observe aquatic and sediment microbes that otherwise could not be grown in a lab in other media. Even today, most of these microbes still cannot be isolated in culture and can only grow together as a complex community.

I chose to use Winogradsky columns in the first lab of my second-semester biology course. Our laboratory curriculum is organized into five units: the scientific method, microbial diversity, plant diversity, animal diversity, and ecosystems. The lab for the first unit begins simply enough: students form small groups, and each group constructs two Winogradsky columns using soil, water, calcium, sulfur, and sources of carbon. One of the columns then gets another nutrient: either iron, magnesium, or nitrogen. Students observe their columns and, in three to six weeks, begin to see stratification of layers. In addition, an oxygen gradient forms in the column, going from aerobes near the surface to anaerobes at the bottom. A sulfur gradient will also develop, with the highest concentration at the bottom of the column. Anaerobes use sulfur and other elements besides oxygen to get energy and grow.

In the weeks that follow in lab, a succession of bacteria, fungi, algae, and protozoa appears. BioInteractive provides a handy interactive resource for exploring the column layers that helps students understand how microbes in one layer release nutrients into, or obtain critical nutrients from, adjoining layers. The “Winogradsky Columns: Microbial Ecology in a Classroom” activity provides additional information on how to set up a column and guide students’ observations.

Different microbial populations appear as pigmented areas in a variety of colors: purple, orange, green, black, or red. As the populations shift and change over the ensuing weeks, we can use these columns to investigate biodiversity beyond prokaryotes, including eukaryotic phyla. Students sample their columns for bacteria, cyanobacteria, protists, algae, and fungi as we cover those topics in lecture. Samples of soil and water from the column are used to teach simple wet mount microscopy, Gram staining, culture and isolation of bacteria on various agar media, protist identification, and metabolic profiles with 32 different sources of carbon. Students use their smartphones to photograph and help ID their organisms, and they include their results in a final report.

With this lab, students become more aware that “biodiversity” starts in the microbial world, and the Winogradsky column serves a micromodel of Earth. Students are visibly excited in the lab when they compare what organisms they have grown in their columns, they rapidly move from microscope to microscope to show each other their findings, and we keep a growing tally on the front board. The final semester unit on ecosystems is no longer an abstract notion, as the students have created their own complex community with biogeochemical cycles. The best confirmation that these concepts have hit home is when students ask if they can take their Winogradsky columns — their miniature planets — home.

Reference
McLean, Mary Ann. “Cheap and Easy Diversity for Introductory Biology.” Proceedings of the Association Reference: for Biology Laboratory Education, 35 (2014): 240–255. http://www.ableweb.org/volumes/vol-35/?art=%2014.