17.1: Prokaryotes

Scientists have studied prokaryotes for centuries, but it wasn’t until 1977 that Carl Woese discovered two distinct lineages within the prokaryotes: Bacteria and Archaea.

Prokaryotes have an important role in changing, shaping, and sustaining the entire biosphere. They can produce proteins and other substances used by molecular biologists in basic research and in medicine and industry. For example, the bacterium Shewanella lives in the deep sea, where oxygen is scarce. It grows long appendages, which have special sensors used to seek the limited oxygen in its environment. It can also digest toxic waste and generate electricity. Other species of prokaryotes can produce more oxygen than the entire Amazon rainforest, while still others supply plants, animals, and humans with usable forms of nitrogen; and inhabit our body, protecting us from harmful microorganisms and producing some vitally important substances.

Prokaryotes are everywhere, playing important roles in the transformation and exchange of nutrients in every ecosystem. In 1966, scientist Thomas Brock discovered that certain bacteria can live in boiling water. This led many to wonder whether prokaryotes may also live in other extreme environments, such as at the bottom of the ocean, at high altitudes, or inside volcanoes, or even on other planets. This chapter will examine some of the diversity, structure, and function of prokaryotes.

Figure $\PageIndex{1}$: Extremophiles in Owens Lake, California. This astronaut photograph highlights the mostly dry bed of Owens Lake, located in the Owens River Valley between the Inyo Mountains (upper left corner) and the Sierra Nevada (bottom). Shallow groundwater, springs, and seeps support minor wetlands and a central brine pool. Two bright red areas along the margins of the brine pool indicate the presence of halophilic (salt-loving) organisms known as archaeans. Gray and white materials within the lake bed are exposed sediments and salt crusts. The nearby towns of Olancha and Lone Pine are marked by the presence of green vegetation, indicating a more constant availability of water. Photograph and caption text from ISS Expedition 28 crew, Public domain, via Wikimedia Commons. Descriptive text: An aerial view of what looks to be a dried up lake bed. There are areas of whitish-grey salt crusts surrounding red pools. A few patches of green can be seen on the borders of the image and in a series of artificial-looking (angular) ponds.

• 2.2.1.1: Cell Structure

  Prokaryotic cells differ from eukaryotic cells in that their genetic material is a single, circular chromosome contained in a nucleoid rather than a membrane-bound nucleus. In addition, prokaryotic cells generally lack membrane-bound organelles. Prokaryotic cells of the same species typically share a similar cell morphology and cellular arrangement. Most prokaryotic cells have a cell wall that helps the organism maintain cellular morphology.

• 2.2.1.2: Archaea

  When these microscopic organisms were first discovered (in 1977), they were considered bacteria. However, when their ribosomal RNA was sequenced, it became obvious that they bore no close relationship to the bacteria and were, in fact, more closely related to the eukaryotes (including ourselves!) For a time they were referred to as archaebacteria, but now to emphasize their distinctness, we call them Archaea.

• 2.2.1.3: Bacteria

  Bacteria are a diverse group of organisms, ubiquitous on planet Earth. These prokaryotes have many important ecological roles, diverse metabolic strategies, and symbiotic relationships with plants. Bacteria were the biosphere's first photosynthesizers.

  • 2.2.1.3.1: Cyanobacteria
  • 2.2.1.3.2: Root Nodules

Attribution

Content from OpenStax modified by Maria Morrow, CC-BY-NC