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5.3: Bacteria Nutrition

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    Can bacteria make their own food from sunlight?

    Plants aren't the only organisms that use the energy of the sun to make food. Some bacteria can also perform photosynthesis. In fact, the first photosynthetic organisms on Earth were bacteria. Photosynthesis is just one of many ways that bacteria can obtain energy.

    Bacteria Nutrition

    Like all organisms, bacteria need energy, and they can acquire this energy through a number of different ways.


    Photosynthetic bacteria use the energy of the sun to make their own food. In the presence of sunlight, carbon dioxide and water are turned into glucose and oxygen. The glucose is then turned into usable energy. Glucose is like the "food" for the bacteria. An example of photosynthetic bacteria is cyanobacteria, as seen in the opening image. These bacteria are sometimes called blue-green algae, although they are not algae, due to their numerous chlorophyll molecules.


    Bacteria known as decomposers break down wastes and dead organisms into smaller molecules. These bacteria use the organic substrates they break down to get their energy, carbon, and nutrients they need for survival.


    Bacteria can also be chemotrophs. Chemosynthetic bacteria, or chemotrophs, obtain energy by breaking down chemical compounds in their environment. An example of one of these chemicals broken down by bacteria is nitrogen-containing ammonia. These bacteria are important because they help cycle nitrogen through the environment for other living things to use. Nitrogen cannot be made by living organisms, so it must be continually recycled. Organisms need nitrogen to make organic compounds, such as DNA.


    Some bacteria depend on other organisms for survival. For example, some bacteria live in the roots of legumes, such as pea plants (Figure below). The bacteria turn nitrogen-containing molecules into nitrogen that the plant can use. Meanwhile, the root provides nutrients to the bacteria. In this relationship, both the bacteria and the plant benefit, also known as mutualism.

    Other mutualistic bacteria include gut microbes. These are bacteria that live in the intestines of animals. They are usually beneficial bacteria, needed by the host organism. These microbes obviously don't kill their host, as that would kill the bacteria as well.

    Bacteria growing on a soybean root help provide the plant with nitrogen
    Figure \(\PageIndex{1}\): These mutualistic bacteria-containing nodules on a soybean root help provide the plant with nitrogen.


    Other bacteria are parasitic and can cause illness. In parasitism, the bacteria benefit, and the other organism is harmed. Harmful bacteria will be discussed in another concept.


    • Bacteria can obtain energy and nutrients by performing photosynthesis, decomposing dead organisms and wastes, or breaking down chemical compounds.
    • Bacteria can obtain energy and nutrients by establishing close relationships with other organisms, including mutualistic and parasitic relationships.

    Explore More

    Use the resources below to answer the questions that follow.

    Explore More I

    1. What are the three nutritional types of bacteria?
    2. What is the base energy source for these three types?
    3. Give an example of a photoautotroph.

    Explore More II

    1. What is the difference between a heterotroph and an autotroph?
    2. What is the difference between aerobic, anaerobic, and facultative anaerobic bacteria?
    3. What are two ways bacteria play important roles in the ecosystem?


    1. Describe two ways that bacteria obtain nutrients and energy?
    2. What is an example of a mutualism with a bacteria?
    3. What is an example of a photosynthetic bacteria.
    4. Describe the importance of chemosynthetic bacteria.

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