Bacteria

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The Carbon Cycle

Bacteria and fungi (yeasts and molds) are vital to another process that makes life on Earth possible: the carbon cycle. They help produce the gas carbon dioxide (CO₂), which plants take from the atmosphere. During a part of the carbon cycle called photosynthesis, plants turn sunlight and CO₂ into food and energy, releasing oxygen into the atmosphere.

The carbon cycle continues after plants and animals die, when bacteria help convert the material of which those organisms are made back into CO₂. Bacteria and fungi secrete enzymes that partially break down dead matter. Final digestion of this matter takes place within bacterial and fungal cells by the processes of fermentation and respiration. The CO₂ released by this action escapes back into the atmosphere to renew the cycle.

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Chemosynthesis

Bacteria are major players in cycles of other elements in the environment. Chemosynthetic bacteria use chemical energy, instead of the light energy used by plants, to change CO₂ into something that other organisms can eat. Chemosynthesis occurs in vents at the bottom of the ocean, where light is unavailable for photosynthesis but hydrogen sulfide gas, H₂S, bubbles up from below Earth’s crust. Life can develop around these vents because bacteria use the H₂S in changing CO₂ into organic nutrients. The H₂S coming up from Earth’s mantle is extremely hot, but bacteria in these vent communities are adapted to the high temperatures. Bacteria’s ability to react chemically with sulfur compounds is useful in certain industrial processes as well.

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Bioremediation

Bioremediation refers to the use of microorganisms, especially bacteria, to return the elements in toxic chemicals to their natural cycles in nature. It may provide an inexpensive and effective method of environmental cleanup, which is one of the major challenges facing human society today.

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Bioremediation has helped in cleaning up oil spills, pesticides, and other toxic materials. For example, accidents involving huge oil tankers regularly result in large spills that pollute coastlines and harm wildlife. Bacteria and other microorganisms can convert the toxic materials in crude oil to harmless products such as CO₂. Adding fertilizers that contain nitrogen, phosphorus, and oxygen to the polluted areas promotes the multiplication of bacteria already present in the environment and speeds the cleanup process.

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Bacteria in Agriculture and Industry

Many of bacteria’s beneficial roles in agriculture have been described in the previous section on Bacteria and the Environment. By recycling certain chemical elements and compounds, bacteria make plant and animal life possible. Bacteria’s chemical interactions have also found uses in industry. In recent decades, scientists have engineered bacterial genes to produce sought-after substances, such as human insulin, to use in the treatment of disease.

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Bacteria in Agriculture

Through the process of nitrogen fixation, bacteria turn nitrogen in the air into nutrients that crops and other plants need to grow. Some of the nitrogen-fixing bacteria attach to the roots of plants. Through the carbon cycle, bacteria produce the carbon dioxide that plants require for photosynthesis. Bacteria that live in the stomachs of cud-chewing animals, such as cows and sheep, help the animals digest grasses.

Bacteria also can be harmful in agriculture because of the major diseases of farm animals they cause. Many of the bacteria that cause infectious diseases in farm animals resemble those that cause similar human diseases. For example, a variant of the bacterium that causes human tuberculosis causes tuberculosis in cattle, and it can infect humans through cow’s milk. To prevent transmission of the disease, milk for human consumption should be pasteurized (heated at a temperature between 60° and 70°C (140° and 158°F) for a short time. Pasteurization kills most bacteria in milk.

Other disease-causing bacteria primarily affect animals other than humans. For example, the bacterium Brachyspira hyodysenteria causes a type of diarrhea in pigs that can be disastrous for pig farmers. Many infectious diseases of farm animals also affect wild animals, such as deer. Wild animals, in turn, can infect domestic animals, including cats and dogs.

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