Nutrition And Metabolism

Prokaryotes have two chief nutritional needs: a source of carbon to build the organic molecules of their cells and a source of energy. They have many ways of getting both carbon and energy from the environment. Organisms that get their carbon from other organisms are called heterotrophs. Autotrophs are organisms that get their carbon directly from the inorganic molecule carbon dioxide, CO2. Organisms that get energy from light are called phototrophs. Chemotrophs get energy from chemicals taken from the environment. Table 23-2 shows how these ways of getting nutrients can be used to divide prokaryotes into four nutritional groups.

TABLE 23-2 Major Bacterial Nutritional Modes

1 Nutritional mode

Energy and carbon source

1 Heterotroph

Photoheterotroph

uses light energy but gets its carbon from other organisms

Chemoheterotroph

obtains both energy and carbon

from other organisms

Autotroph

Photoautotroph

uses light energy and gets carbon from CO2

Chemoautotroph

extracts energy from inorganic compounds and uses CO2 as a carbon source

i i

figure 23-9

Prokaryotes that have different pigments live at different temperatures in a Yellowstone hot spring. Some are photoautotrophs, some are chemoautotrophs, and others are chemoheterotrophs.

figure 23-9

Prokaryotes that have different pigments live at different temperatures in a Yellowstone hot spring. Some are photoautotrophs, some are chemoautotrophs, and others are chemoheterotrophs.

figure 23-10

Thermus aquaticus cells form a long, stringy mass in the outflow channel of a hot spring. T. aquaticus was first isolated from a hot spring in Yellowstone by Thomas D. Brock. Later, the heat-tolerant enzyme Taqpolymerase was isolated from T. aquaticus. Biotechnologists now routinely use Taq polymerase to rapidly replicate pieces of DNA in the polymerase chain reaction (PCR).

figure 23-10

Thermus aquaticus cells form a long, stringy mass in the outflow channel of a hot spring. T. aquaticus was first isolated from a hot spring in Yellowstone by Thomas D. Brock. Later, the heat-tolerant enzyme Taqpolymerase was isolated from T. aquaticus. Biotechnologists now routinely use Taq polymerase to rapidly replicate pieces of DNA in the polymerase chain reaction (PCR).

Most prokaryotes that we have studied so far are photoautotrophs (FOHT-oh-AWT-oh-TROHFS) and chemoheterotrophs (KEE-moh-HET-uhr-oh-TROHFS). Prokaryotes such as cyanobacteria that gather sunlight for photosynthesis are photoautotrophs. Photoautotrophs harvest energy with light-trapping compounds similar to those of plants. Chemoautotrophs, a group of autotrophs, oxidize inorganic compounds to get energy. For example, members of the genus Nitrosomonas oxidize ammonia, NH3, forming nitrite, NO2, and use the released energy. Methanogens living in a cow's digestive tract make methane gas from inorganic molecules. Pathogenic (disease-causing) bacteria are chemoheterotrophs. Figure 23-9 shows an environment in which various prokaryotes that have different kinds of nutritional needs live close together.

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