Microbiology, 2021

CHAPTER 4
Prokaryotic Diversity
Figure 4.1 The bacterium Shewanella lives in the deep sea, where there is little oxygen diffused in the water. It is
able to survive in this harsh environment by attaching to the sea floor and using long appendages, called
“nanocables,” to sense oxygen. (credit a: modification of work by NASA; credit b: modification of work by Liza Gross)
Chapter Outline
4.1 Prokaryote Habitats, Relationships, and Microbiomes
4.2 Proteobacteria
4.3 Nonproteobacteria Gram-Negative Bacteria and Phototrophic Bacteria
4.4 Gram-Positive Bacteria
4.5 Deeply Branching Bacteria
4.6 Archaea
INTRODUCTION Scientists have studied prokaryotes for centuries, but it wasn’t until 1966 that scientist
Thomas Brock (1926–) 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.
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. This chapter will examine the diversity, structure, and function of prokaryotes.