Bacteria that Form Storage Granules

A number of aquatic bacteria form granules that serve to store nutrients. Recall that anoxygenic phototrophs often store sulfur granules, which can later be used as a source of electrons for reducing power. Some bacteria store phosphate, and others store compounds that can be used to generate ATP.

The Genus Spirillum

Members of the genus Spirillum are Gram-negative spiral-shaped, microaerophilic bacteria. Spirillum volutans forms volutin granules, which are storage forms of phosphate. These are sometimes called metachromatic granules to reflect their characteristic staining with the dye methylene blue. The cells of S. volutans are typically large, over 20 mm in length. In wet mounts, Spirillum species may be seen moving to a narrow zone near the edge of the coverslip, where O2 is available in the optimum amount. ■ volutin, p. 67

Sulfur-Oxidizing, Nitrate-Reducing Marine Bacteria

Some marine bacteria store both sulfur, which can be oxidized as an energy source, and nitrate, which can serve as an electron acceptor. This provides an advantage to the bacteria, because anaerobic marine sediments are often abundant in reduced sulfur compounds but deficient in suitable terminal electron acceptors. In contrast, waters above those sediments lack reduced sulfur compounds but provide a source of nitrate. In other words, the energy source and terminal electron acceptor do not coexist. Thioploca species respond by forming long sheaths within which filamentous cells shuttle between the sulfur-rich sediments and nitrate-rich waters, storing reserves of sulfur and nitrate in order to obtain energy.

Scientists recently discovered a huge bacterium in the ocean sediments off the coast of the African country of Namibia that they named Thiomargarita namibiensis, "sulfur pearl of Namibia" (see Perspective 1.1). The cells are a pearly white color due to globules of sulfur in their cytoplasm. The cells each contain a large nitrate storage vacuole. It is thought that these organisms, which may reach a diameter of % mm, can store a 3-month supply of sulfur and nitrate. The cells are not motile and instead appear to rely on occasional disturbances such as storms to bring them into contact with the nitrate-rich water.

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Responses

  • Habaccuc
    How does E.coli obtains energy from its storage granules?
    2 years ago
  • jessamine
    How does e.coli obtain energy from its storage granules?
    11 months ago

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