Types of Autotrophic Bacteria

Autotrophic bacteria can produce their own food. ("Auto" means "self" and "troph" means "nourishment.") Five common types of autotrophic bacteria are cyanobacteria, green sulfur bacteria, purple bacteria, methanogens and halophiles.

Cyanobacteria

• Cyanobacteria are blue-green algae. Athough unrelated to other types of algae, cyanobacteria live in watery environments and produce their own food with energy gleaned from sunlight. Because of this ability, scientists label cyanobacteria as "photoautotrophs." ("Photo" means "light.")

  Chloroplast found in plants is actually cyanobacteria. This green substance allows photosynthesis, the process that plants use to nourish themselves. More precisely, photosynthesis converts carbon dioxide and sunlight into oxygen and sugar.

  Cyanobacteria are some of the most ancient organisms on earth. Scientists have found cyanobacteria fossils that are more than 3.5 billion years old.

Green Sulfur Bacteria

• Green sulfur bacteria, as their name suggests, grow where sulfur is present. They are also thermophilic, which means they thrive in hot environments. For example, scientists have found them in hot springs in New Zealand.

  Like cyanobacteria, green sulfur bacteria are photoautotrophs. But unlike cyanobacteria, the photosynthesis of green sulfur bacteria does not produce oxygen. In fact, green sulfur bacteria have a low tolerance for oxygen and can grow without much exposure to light.

  Some scientists suspect that green sulfur bacteria might supply an alternative form of energy. For that reason, research on them has increased in recent years. A major breakthrough was the DNA sequencing of Chlorobium tepidum, a specific type of green sulfur bacteria.

Purple Bacteria

• Purple bacteria are named for their color, although some types appear reddish or brownish. They are also photoautotrophs, and, like green sulfur bacteria, their photosynthesis does not produce oxygen. Instead, the photosynthesis of purple bacteria produces sulfur.

  Purple bacteria belong to the Proteobacteria phylum, one of the groupings scientists use to show how bacteria are related. Other members of this phylum include salmonella and nitrogen-fixing bacteria.

  The U.S. Air Force has shown a special interest in purple bacteria and has considered using it to power drone planes.

Methanogens

• Rather than producing food from sunlight, methanogens rely on a chemical reaction called oxidation. During oxidation, methanogens take in carbon from the environment and, with the help of hydrogen gas, create methane.

  Bacteria that use chemical reactions to produce their food are known as "chemoautotrophs."

  Methanogens call many places home. Some live in marshes and swamps, some live in the intestines of humans and animals, and some live in hot springs and ocean vents. Scientists also have found methanogens in solid rocks.

Halophiles

• Halophiles are another type of chemoautotroph. Their name means "salt lover," and they live where salt is abundant. Scientists have found halophiles that flourish in the Great Salt Lake, the Dead Sea and Lake Magadi. Other halophiles prefer less extreme environments such as inland seas.

  Halophiles play a role in some processed foods. Soy sauce and pickled fish, for instance, both require halophilic bacteria.