Scientists once thought that sunlight was source of energy for all life and that photosynthesis was the only way to make food. It is now known that reduced chemicals from hydrothermal vents provide chemosynthetic energy for some lifeforms. High temperatures and high concentrations of dissolved minerals in seawater form compounds such as hydrogen sulfide. In a biochemical process, bacteria oxidize hydrogen sulfide and use the liberated energy to produce carbohydrates (i.e., stored chemical energy). Unlike photosynthesis, chemosynthesis requires no light and can occur at the extreme temperatures and high pressures of the deep ocean. The chemosynthetic food web supports dense populations of uniquely-adapted organisms.

Chemosynthetic bacteria may be one of the oldest life forms on Earth. The classic Winogradsky column --developed long before hydrothermal vent ecosystems were discovered -- provides an excellent illustration of bacterial growth and succession. In 1880, the Russian scientist Sergei Winogradsky discovered the bacteria Beggiatoa. These bacteria metabolize hydrogen sulfide to produce the energy for making carbohydrates. Beggiatoa is among the bacteria found in the deep-sea hydrothermal vent environment, but it is not the only bacteria to take advantage of this chemosynthetic process.
In this activity, students will grow and observe succession and chemosynthesis of bacterial colonies: one lighted, the other in the dark. This activity uses the concepts of the Winogradsky column, a device which enriches and isolates certain organisms involved in the sulfur and nitrogen cycles. The activity provides a rough analog to both processes of chemosynthesis and succession; processes which occur at deep sea hydrothermal vents and form the base of the food web in the absence of sunlight.
  • Some organisms cannot draw energy from the sun and must find other energy sources to live
  • Both photosynthesis and chemosynthesis are means of producing carbohydrates
  • Photosynthetic organisms use light as their energy source; chemosynthetic organisms use chemicals
  • As organisms thrive in a given environment, their by-products create a new environment where new species can succeed
FOR EACH GROUP: Two 500 milliliter graduated cylinders or columns, Enough black mud to fill these cylinders, 80 grams of CaSO4 (Plaster of Paris: found in any hardware store), 20 jars or beakers for mixing, Stirring rods, Organic straw or filter paper bits (e.g., torn strips of lab filter paper), 3 liters of pond water (or seawater or swamp water), 4 grams baking soda, 20 multivitamin pills and something with which to crush them, Plastic wrap, Rubber bands, Light source that can stay on for at least six weeks, Tape and markers for labeling columns, Flashlight with red cellophane on lighted end
Divide the class into pairs or small groups. Each pair of students will set up two identical columns. One will be kept in the dark and the other will be placed under a light source. Obtain mud from a local lake, river, or bay or estuary. If it is not completely black let the mud sit for awhile in a jar to blacken.
Before the experiment begins, give students a tutorial on what to look for in their cylinders. In the first week, students should see green-colored algae in the well-lit column. Then, over a period of six weeks, at least five different bacteria may grow in succession in both columns. It is difficult to know exactly what bacteria are actually growing in the columns. The first species may be the anaerobic (i.e., living in the absence of oxygen) bacterium Clostridium; this heterotroph (i.e., requires organic material for food) would use the straw or filter paper as a carbon source to produce food. Another bacterium, Desulfovibrio, may use the waste of Clostridium as its source of carbon and CaSO4 as an energy source. Desulfovibrio may produce the hydrogen sulfide required by the rest of the ecosystem. Three other bacteria -- Beggiatoa (white or yellow), Chlorobium (green), and Chromatium (purple and violet) -- use hydrogen sulfide as part or all or their energy source to make food; because they also require oxygen, you will find these bacteria near the surface of the sediments. After formation of purple and green bacterial patches, black spots of hydrogen sulfide will likely appear. Hydrogen sulfide will be identifiable by its distinctive odor.
  1. Add about four grams of CaSO4 to enough mud to fill one graduated cylinder to a depth of about 8.0 cm (3.2 inches). Dump the mixture into a jar or beaker and stir it thoroughly with the stirring rod.
  2. Place the straw or filter paper in the jar with the mud and mix gently. (It may help to add some pond/swamp/sea water here to ease stirring.)
  3. Transfer the mixture back to the cylinder and add pond or seawater so that the mud is covered with at least 8 centimeters (3.2 inches) of water.
  4. Add to the cylinder 0.2 grams of baking soda and one crushed vitamin pill. Stir again to make sure all the air bubbles are gone.
  5. Set the cylinder aside for 30 minutes to settle.
  6. After 30 minutes, if more than two centimeters (0.8 inches) of water have pooled at the top, pour off all but one centimeter (0.4 inches). If there is less than one centimeter of pooled water on top, add pond/swamp/sea water.
  7. Repeat steps (1) through (6) for the other graduated cylinder.
  8. Label the cylinders with the students' names.
  9. Place one graduated cylinder in a darkened area where it will not be disturbed for at least six weeks. Place the second cylinder under the light source. (You may wish to store both set-ups in the same area with one cylinder in a box. This will help to keep both in similar conditions.)
  10. Record smell, color, number of layers of mud, or any other observations.
  • For at least six weeks, examine the columns weekly and look for signs of bacterial growth. You may wish to use a safety light (flashlight covered with red cellophane) to examine the columns being grown in the dark. Record your observations.
  • Bacteria that use light as their major energy source with some hydrogen sulfide are heterotrophic. Bacteria that use hydrogen sulfide for energy in the absence of light are chemotrophic.
    • Are the bacteria in your well-lit and darkened columns similar? Based on your results and the description above, can you distinguish which bacteria are heterotropic? Chemotrophic?
  • Discuss how the by-products created by some types of bacteria were used by other types of bacteria that then became the dominant species. (This process is called "succession.")
    • Can the students name other examples of "species succession"?
  • (OPTIONAL) At the end of the third week take samples for microscopic wet mounts observation from the following locations: (1) surface layers of water, (2) surface layers of the mud, (3) colored layer from the mud. Try using a pipette and be careful not to disturb the column. Observe the wet mounts under high-power magnification, looking for cell shapes that would indicate the types of organisms present.
Adapted from Orange County Marine Institute / San Juan Institute Activity Series AND "Visit to an Ocean Planet" CD-ROM, Copyright 1998, California Institute of Technology and its licenses.