3: Prokaryotic Diversity

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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.

3.1: Cells as Living Things
The theory of spontaneous generation states that life arose from nonliving matter. It was a long-held belief dating back to Aristotle and the ancient Greeks. Experimentation by Francesco Redi in the 17th century presented the first significant evidence refuting spontaneous generation by showing that flies must have access to meat for maggots to develop on the meat. Louis Pasteur is credited with conclusively disproving the theory and proposed that “life only comes from life.”
3.2: Unique Characteristics of Prokaryotic Cells
Prokaryotic cells differ from eukaryotic cells in that their genetic material is 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 and protects it against changes in osmotic pressure.
3.3: Classifying Prokaryotes and Examples
Highlights from the various groups of Bacteria and Archaea and what we use to distinguish them.
3.4: Bacterial Infections of the Skin and Eyes
Staphylococcus and Streptococcus cause many different types of skin infections, many of which occur when bacteria breach the skin barrier through a cut or wound. S. aureus are frequently associated with purulent skin infections that manifest as folliculitis, furuncles, or carbuncles. S. aureus is also a leading cause of staphylococcal scalded skin syndrome (SSSS). S. aureus is generally drug resistant and current MRSA strains are resistant to a wide range of antibiotics.
3.5: Bacterial Infections of the Respiratory Tract
The respiratory tract can be infected by a variety of bacteria, both gram positive and gram negative. Although the diseases that they cause may range from mild to severe, in most cases, the microbes remain localized within the respiratory system. Fortunately, most of these infections also respond well to antibiotic therapy.
3.6: Bacterial Infections of the Urinary System
Urinary tract infections (UTIs) include infections of the urethra, bladder, and kidneys, and are common causes of urethritis, cystitis, pyelonephritis, and glomerulonephritis. Bacteria are the most common causes of UTIs, especially in the urethra and bladder. Bacterial cystitis is commonly caused by fecal bacteria such as E. coli. Pyelonephritis is a serious kidney infection that is often caused by bacteria that travel from infections elsewhere in the urinary tract.
3.7: Bacterial Infections of the Reproductive System
In addition to infections of the urinary tract, bacteria commonly infect the reproductive tract. As with the urinary tract, parts of the reproductive system closest to the external environment are the most likely sites of infection. Often, the same microbes are capable of causing urinary tract and reproductive tract infections. Bacterial vaginosis, Chlamydia, Gonorrhea, and Chancroid are diseases caused by bacteria.
3.8: Bacterial Infections of the Gastrointestinal Tract
Major causes of gastrointestinal illness include Salmonella spp., Staphylococcus spp., Helicobacter pylori, Clostridium perfringens, Clostridium difficile, Bacillus cereus, and Yersinia bacteria. C. difficile is an important cause of hospital acquired infection. Vibrio cholerae causes cholera, which can be a severe diarrheal illness. Different strains of E. coli, including ETEC, EPEC, EIEC, and EHEC, cause different illnesses with varying degrees of severity.
3.9: Bacterial Infections of the Circulatory and Lymphatic Systems
Bacterial infections of the circulatory system are almost universally serious. Left untreated, most have high mortality rates. Bacterial pathogens usually require a breach in the immune defenses to colonize the circulatory system. Most often, this involves a wound or the bite of an arthropod vector, but it can also occur in hospital settings and result in nosocomial infections.
3.10: Bacterial Diseases of the Nervous System
Bacterial infections that affect the nervous system are serious and can be life-threatening. Fortunately, there are only a few bacterial species commonly associated with neurological infections.
3.11: Exercises

Thumbnail: A cladogram linking all major groups of living organisms to the LUCA (the black trunk at the bottom), based on ribosomal RNA sequence data.