BSC 310 Lecture Notes - Lecture 25: Aquaspirillum, Spirillum, Leptospira Interrogans
Archaebacteria
Archaebacteria differ from all other bacteria (which are sometimes called eubacteria).
Archaebacteria are so named because biochemical evidence indicates that they evolved
before the eubacteria and have not undergone significant change since then. The
archaebacteria generally grow in extreme environments and have unusual lipids in their cell
membranes and distinctive RNA molecules in their cytoplasm.
One group of archaebacteria are the methanogens, anaerobic bacteria found in swamps,
sewage, and other areas of decomposing matter. The methanogens reduce carbon dioxide
to methane gas in their metabolism. A second group are the halobacteria, a group of rods
that live in high‐salt environments. These bacteria have the ability to obtain energy from
light by a mechanism different from the usual process of photosynthesis. The third type of
archaebacteria are the extreme thermophiles. These bacteria live at extremely high
temperatures, such as in hot springs, and are associated with extreme acid environments.
Like the other archaebacteria, the extreme thermophiles lack peptidoglycan in their cell
walls. Many depend on sulfur in their metabolism, and many produce sulfuric acid as an
end‐product.
Submicroscopic Bacteria
Rickettsiae. Rickettsiae are rod‐shaped and coccoid bacteria belonging to the order
Rickettsiales. These bacteria cannot be seen with the light microscope, and therefore the
Gram stain is not used for identification. However, their walls have the characteristics of
Gram‐negative cell walls. Rickettsiae are obligate intracellular parasites that infect humans
as well as arthropods such as ticks, mites, and lice. They are cultivated only with great
difficulty in the laboratory and generally do not grow on cell‐free media. Tissue cultures and
fertilized eggs are used instead.
Rickettsiae are very important as human pathogens. Various species cause Rocky Mountain
spotted fever, epidemic typhus, endemic typhus, scrub typhus, Q fever, and ehrlichiosis.
Chlamydiae. Chlamydiae are extremely tiny bacteria, below the resolving power of the light
microscope. Although the Gram stain is not used for identification, the bacteria have cell
walls resembling those in Gram‐negative bacteria.
Chlamydiae display a growth cycle that takes place within host cells. The bacteria invade the
cells and differentiate into dense bodies called reticulate bodies.The reticulate bodies
reproduce and eventually form new chlamydiae in the host cell called elementary
bodies. Chlamydiae cause several diseases in humans, such as psittacosis, a disease of the
lung tissues; trachoma, a disease of the eye; and chlamydia, an infection of the
reproductive tract.
Mycoplasmas. Mycoplasmas are extremely small bacteria, below the resolving power of the
light microscope. They lack cell walls and are surrounded by only an outer plasma
membrane. Without the rigid cell wall, the mycoplasmas vary in shape and are said to
be pleomorphic. Certain species cause a type of mild pneumonia in humans as well as
respiratory tract and urinary tract diseases.
Spirochetes and Spirilla
Over 400 recognized genera of bacteria are known to exist. Bacterial species are listed
in Bergey's Manual of Systematic Bacteriology. The entire kingdom of bacteria, including
cyanobacteria, is entitled Prokaryotae. Four divisions of bacteria based on their cell wall
characteristics are included in the Prokaryotae kingdom. Not all bacteria are assigned to a
division, but all are assigned to one of 33 “sections.”
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Document Summary
Archaebacteria differ from all other bacteria (which are sometimes called eubacteria). Archaebacteria are so named because biochemical evidence indicates that they evolved before the eubacteria and have not undergone significant change since then. The archaebacteria generally grow in extreme environments and have unusual lipids in their cell membranes and distinctive rna molecules in their cytoplasm. One group of archaebacteria are the methanogens, anaerobic bacteria found in swamps, sewage, and other areas of decomposing matter. The methanogens reduce carbon dioxide to methane gas in their metabolism. A second group are the halobacteria, a group of rods that live in high salt environments. These bacteria have the ability to obtain energy from light by a mechanism different from the usual process of photosynthesis. The third type of archaebacteria are the extreme thermophiles. These bacteria live at extremely high temperatures, such as in hot springs, and are associated with extreme acid environments.
