Column Kingdoms Reading
Microbial Ecology Lab Guide
Column Kingdoms: Life in a Jar of Mud
Name:
Date:
In the 1880s, Russian microbiologist Sergei Winogradsky invented a simple yet profound experiment: seal pond mud, water, shredded paper (cellulose carbon), and eggshells or gypsum (sulfate) inside a clear tube, place it by a window, and wait. Over weeks, this stagnant sludge transforms into a vibrant, living rainbow. The column creates miniature vertical worlds where diverse microbial communities segregate according to light, oxygen, and sulfur.
O₂
Oxygen Gradient
Highest at the open top; drops to zero below
HIGH ↓ ZERO
H₂S
Sulfide Gradient
Produced at deep base; diffuses upward
ZERO ↑ HIGH
Top Zone
Water Surface
Bright Green
Cyanobacteria & Green Microalgae (Aerobic Photosynthesizers)
Bathed in direct sunlight and fresh air, these organisms perform standard oxygen-releasing photosynthesis using water, just like plants. They enrich the upper water with oxygen ($O_2$) and fix carbon dioxide into sugars, nourishing floating aerobic protozoa and heterotrophs.
Upper Mud
Microaerophilic
Rust / Cream
Colorless Sulfur & Iron Oxidizers (e.g., Beggiatoa, Thiobacillus)
Living right at the chemical battlefront where trace oxygen meets rising hydrogen sulfide gas. They obtain metabolic energy by oxidizing poisonous sulfide into harmless sulfate ($SO_4^{2-}$), effectively creating a chemical buffer that keeps deeper toxic gases from escaping into the air.
Mid Mud
Anaerobic Light
Purple & Green
Purple & Green Sulfur Bacteria (Anoxygenic Phototrophs)
Oxygen is lethal to these microbes! Instead of water, Chromatium (purple sulfur) and Chlorobium (green sulfur) use hydrogen sulfide as an electron donor for photosynthesis. They absorb longer infrared light wavelengths that pass right through the green algae above, producing pure sulfur granules rather than oxygen.
Deep Mud
Strict Anoxic
Jet Black Base
Sulfate-Reducing Bacteria & Fermenters (e.g., Desulfovibrio, Clostridium)
Pitch-black, zero oxygen, and rich in buried cellulose. Fermenters first break down shredded newspaper into organic acids. Then, sulfate reducers "breathe" sulfate ($SO_4^{2-}$) and release hydrogen sulfide gas ($H_2S$). The $H_2S$ reacts with iron in the soil to precipitate black iron sulfide ($FeS$), dyeing the mud pitch black!
Key Takeaway: The waste product of one microbial layer serves as the vital fuel source for the layer above it.
Investigation & Analysis
Winogradsky Column Comprehension
Microbiology Core Concepts
Part I & II: Questions
A Chemical Gradients & Conditions
1. Which gas is abundant at the top of the column but completely absent in the deep mud?
2. Where is hydrogen sulfide ($H_2S$) produced, and which direction does it diffuse?
B Microbe Profiling: Match the Organism
Write the correct microbial group next to each description below: Cyanobacteria, Sulfate-Reducers, Purple Sulfur Bacteria, Colorless Sulfur Oxidizers.
a. Strictly anaerobic phototrophs that absorb infrared light and use $H_2S$ instead of water:
b. Oxygen-generating microbes forming bright green patches at the sunlit surface:
c. Deep-dwelling anaerobes that produce $H_2S$ gas, reacting with iron to turn mud black:
d. Microbes living at the oxygen/sulfide boundary that convert toxic $H_2S$ back into sulfate:
C Ecological Reasoning & Predictions
3. Metabolic Interdependence: How do sulfate-reducing bacteria at the bottom and purple/green sulfur bacteria in the middle depend on one another in a closed nutrient loop?
4. Experimental Prediction: A student completely wraps the bottom half of their Winogradsky column in opaque black electrical tape, blocking all light from reaching the middle and bottom layers. What will happen to the purple and green sulfur bacteria? Explain why.
5. The Oxygen Boundary: Why are purple and green sulfur bacteria strictly confined to the deeper layers rather than flourishing at the bright, sunlit water surface?
Winogradsky Column Ecological Reading Series Total Score: / 20
