Building Biospheres in a Bottle

In Room 804, two students peeled hard-boiled eggs, sweeping the shells into a neat pile. Across from them, a classmate crushed multi-vitamins with a mortar and pestle. At the table by the window, others sifted through things they had brought in from outside: sticks, leaves and a handful of ear-shaped mushrooms.

Welcome to “Disease Detectives,” a far-reaching Upper School FOCUS course that examines the robust world of microorganisms, including disease-causing pathogens. On this particular day, Dr. Hood was leading a decidedly hands-on (and quite messy!) lesson that would introduce her Class 10 and 11 students to the vast diversity of microbial life and the unique ecological environments species thrive in.

“Today we’re creating biospheres in a bottle,” she announced, kicking off the afternoon lesson by distributing empty plastic liter bottles to pairs of students.

Officially known as the “Winogradsky Column,” this technique was invented in the 1880s by Sergei Winogradsky (1856-1953), a Russian scientist and one of the founders of modern microbiology. Today, more than a century later, the aim of this simple ecosystem remains as compelling as ever: to observe, over time, organisms in their natural habitats.

After carefully cutting the tops off their bottles (about two inches below the “neck”), the students were ready to begin to build their biospheres. First, with gloved hands, they scooped generous portions of potting soil from oversized bags, packing the vessels about two-thirds full.

For this method to be successful, their bottles needed hydration as well as nutrients. Although the original experiment called for pond water, Dr. Hood substituted with what was most readily available. After moistening the dirt with tap water from the lab’s faucet, the students used wooden paint stirrers to blend wet and dry together. It took a bit of trial and error to achieve the right consistency – not too loose but muddy enough to promote vigorous growth.

To further fortify their biospheres, the students were encouraged to incorporate a variety of ingredients, including those containing sulfur and carbon, known to promote microbial development. Dr. Hood explained that eggs were especially valuable, not just the yolks, which have high sulfur levels, but the actual shells, which are rich in carbon.

Discovering that paper, too, has significant carbon properties, several students tore up scrap sheets and tossed the pieces into their bottles. Others opted to add calcium carbonate in powder form, which they measured out using the lab’s portable balance device, and vitamins, which they learned were more readily absorbed when ground.

Productive chatter filled the sunny space as the students worked efficiently – and with much enthusiasm – to thoughtfully assemble their biospheres. They also recorded all the steps they took in their science notebooks.

“Anyone want to add a nail?” asked Dr. Hood. Two students jumped at the offer, happy to boost their bottles with an extra dose of iron. Flora specimens, including tendrils of basil, a crust of bark, a bag of grass clippings, and a small pinecone, were among the items spilled out on the tables.

When their bottles were complete, the students added another bit of water to seal the contents, then put the cut-off tops back on but in an inverted position to keep their mixtures secure. To minimize gas leakage and odors, each biosphere was ensconced in plastic wrap with a handful of holes poked in the surface.

Stressing that “light is a key ingredient,” Dr. Hood helped her students line up their bottles along the windowsill before they all pitched in to clean up the lab. Throughout the term, the class will regularly check on the progress of their self-contained universes, investigating the fascinating life percolating within. “I’m so excited to see what grows!” said Dr. Hood. Her students were clearly in agreement.