Download Notes Chapter 24 Bacteria

24 Bacteria
1. Bacteria differ from eukaryotes in at least seven ways:
A. Internal compartmentalization: they have not internal compartments or membrane
systems
B. Cell size: most bacterial cells are about 1um in diameter; most eukaryotic cells are more
than 10 times that size
C. Multicellularity: all bacteria are single cells
D. Chromosomes: bacterial chromosomes consist of a circular piece of DNA.
E. Reproduction: bacteria reproduce by binary fission
F. Flagella: bacterial flagella are simple structures composed of a single fiber of protein that
spins like a corkscrew to move the cell. Some bacteria also have pili. Pili allow bacteria
to attach to surfaces or to other cells
G. Metabolic diversity: bacteria have more metabolic abilities than eukaryotes.
a. Bacteria can do both aerobic and anaerobic processes
2. Define bacteria, eubacteria, and archaebacteria, and note the relationships between them
A. Bacteria are microscopic prokaryotes
1) Bacteria are the most numerous organisms on Earth as well as the most ancient
a. They were probably the first forms of life
b. It is likely that all other organisms evolved from bacteria
2) By comparing ribosomal RNA sequences, scientists have found that there are two
vastly different types of bacteria
a. The bacteria that we generally refer to as germs are classified in the kingdom
Eubacteria
(1) In this text, members of the kingdom Eubacteria are sometimes referred to as
eubacteria, but more frequently, members of this kingdom are simply called
bacteria
b. The other type of bacteria are called archaebacteria
(1) These bacteria, which are more ancient than the eubacteria, are
classified in the kingdom Archaebacteria
a. unusual have lipids in their cell membranes and have introns in their DNA
b. Their cell walls are characterized by the absence of peptidoglycan, a proteincarbohydrate compound found in the cell walls of eubacteria
c. have some genes that resemble eubacterial genes, and genes that closely
resemble those found in eukaryotes
d. This suggests that they probably evolved from an ancestral organism that
gave rise to other forms of life on Earth
e. Archaebacteria were first discovered in extreme environments, such as
swamps, salt lakes, and hot springs
3. Describe the methods used to classify bacteria
A. Unlike most other organisms, bacteria have few morphological differences that can be
used to classify them
1) For example, bacteria do not vary in size and shape to the extent that other types of
organisms do
2) Traditionally, bacteria have been grouped based on their structure, physiology,
molecular composition, and reaction to specific types of stains, rather than on their
evolutionary relationships
B. Gram Stain
1) Most species of eubacteria can also be grouped into two categories based on their
response to a laboratory technique called the Gram stain
a. Gram-positive bacteria retain the Gram stain and appear purple under the
microscope
(1) Because Gram-positive bacteria have a thicker layer of peptidoglycan
in their cell wall than Gram-negative bacteria do, they are able to
retain the Gram stain
b. Gram negative bacteria do not retain the purple stain and take up a second pink
stain instead
(1) Gram-positive and Gram-negative bacteria also differ in several other
ways
(2) It is important to know whether a bacterium is gram-positive or gramnegative because this will tell the doctor which kind of antibiotics to
treat the patient with
(3) Antibiotics are chemicals that interfere with life processes in bacteria
4. Name and describe three known types of archaebacteria
A. Methanogens, are named for their unique method of harvesting energy by converting H2
and CO2 into methane gas
1) Because oxygen is a poison to them, methanogens can live only in anaerobic
conditions, such as at the bottom of a swamp and in sewage, where they are the source
of marsh gas
2) They can also be found thriving in the intestinal tracts of humans and other animals,
such as cows
B. Extreme halophiles, which are salt-loving, live in environments with very high salt
concentrations, such as the Great Salt Lake and the Dead Sea
1) High salt concentrations would kill most bacteria, but this high concentration is
beneficial to the growth of extreme halophiles, and these organisms use salt to
generate ATP
C. Thermoacidophiles live in extremely acidic environments that have extremely high
temperatures, such as hot springs
1) Some thermoacidophiles thrive at temperatures up to 110°C (230°F) and at a pH of
less than 2
2) Thermoacidophiles live near volcanic vents on land or near hydrothermal vents,
cracks in the ocean floor miles below the surface that leak scalding acidic water
5. Describe the structure of a bacterial cell
A. There are 3 basic shapes; bacillus (rod-shape), coccus (round-shape), and
spirillum (spiral shape)
1) Most bacteria have a cell wall. Some also have a capsule, which is a
gel-like layer that further protects the cell. The capsule is located outside
of the cell wall
B. Structure - Bacteria are typically composed of a cell wall, a cell membrane, and
cytoplasm
C. Cell Wall
1) With a few exceptions, both eubacteria and archaebacteria have a cell wall made of
peptidoglycan (short chains of amino acids, or peptides, and carbohydrates)
2) In Gram-negative eubacteria, the cell wall includes an outer membrane that is
composed of a layer of lipids and sugars
a) The outer membrane protects these bacteria against some kinds of antibiotics by
preventing their entry into the cell
D. Cell Membrane and Cytoplasm
1) The bacterial cell membrane, which is composed of a lipid bilayer, is
similar to the eukaryotic cell membrane
a) However, in bacteria, the cell membrane contains the enzymes
that catalyze the reactions of cellular respiration
b) The cell membranes of photosynthetic bacteria have internal foldings called
thylakoids homologous to the thylakoids found in plant chloroplasts
2) Unlike eukaryotic cells, bacterial cells do not contain membranebound organelles
a. The cytoplasm of bacterial cells is made of a viscous solution of ribosomes and
DNA
b. The bacterial DNA is arranged in a single, closed loop
c. In addition to the main chromosome, some species of bacteria also have
plasmids, self-replicating loops of DNA, in their cytoplasm
E. Capsules and Pili
1) Many bacterial species produce an outer covering called a capsule
a. The capsule is made of polysaccharides that cling to the surface of the cell and
protect it against drying or harsh chemicals and from the host body’s white blood
cells, which could otherwise engulf it
2) Pili are short, hairlike protein structures found on the surface of some species of
bacteria
a. Pili help bacteria adhere to host cells
b. Pili are also used to transfer genetic material from one bacterium to another
c. A bacterium with pili can join with a bacterium that doesn’t have pili, and can
transfer some of its DNA to that other bacterium (conjugation). This is part of the
reason we have so much antibiotic resistance
F. Endospores
1) A bacterial endospore is a dormant structure that is produced by some Gram-positive
bacterial species that are exposed to harsh environmental conditions
2) Endospores consist of a thick outer covering that surrounds the cell’s DNA
3) Although the original cell may be destroyed by harsh conditions, its endospore will
survive
a. When conditions become favorable, the endospore will open, allowing the living
bacterium to emerge and to begin multiplying
6. Describe three ways that bacteria move
1) Many bacteria use flagella to move
a. Flagella, which are made of protein, turn and propel the bacterium in an erratic,
“run-and-tumble” motion
b. Bacteria can have a single flagellum or a tuft of flagella
c. Some species of bacteria have flagella at both ends of the cell, and other species of
bacteria are completely surrounded by flagella
2) The bacteria that lack flagella have other methods of movement
a. Myxobacteria produce a layer of slime and then glide through it
(1) Wavelike contractions of the outer membrane propel the organism through the
slime
b. Some spiral-shaped bacteria move by a corkscrew-like rotation
(1) These organisms have flexible cell walls and filaments within the cell walls
that, when contracted, cause the bacterium to turn and move ahead
7. Compare the heterotrophic modes of nutrition in bacteria with the autotrophic modes
A. Depending on the species, bacteria may be heterotrophic or autotrophic
1) Heterotrophic bacteria use organic matter as a source of nutrition
a. Heterotrophic bacteria that feed on dead and decaying material are called
saprophytes
2) Autotrophic bacteria obtain their energy from sunlight or minerals
a. Bacteria that use sunlight as an energy source, such as cyanobacteria, are called
photoautotrophs
(1) These autotrophs use light-trapping compounds similar to those used by
plants to obtain energy
(2) Can be classified into 4 major groups based on the photosynthetic
pigments they contain: purple nonsulfur bacteria, green sulfur bacteria,
purple sulfur bacteria, and cyanobacteria
a. Green sulfur and purple sulfur bacteria grow anaerobically (w/out oxygen)
b. They use sulfur compounds, like hydrogen sulfide, as a source of electrons
b. Chemoautotrophs oxidize inorganic compounds to obtain energy
(1) Members of the genus Nitrosomonas oxidize ammonia, NH3, to form
nitrite, NO2, and harvest the resulting energy
(2) Obtain energy by removing electrons from inorganic molecules such as
ammonia, hydrogen sulfide, or organic molecules like methane
(3) They usually live in the soil
c. Many bacteria are obligate anaerobes, which means they cannot survive in the
presence of oxygen
(1) The obligate anaerobe Clostridium tetani causes tetanus
d. Facultative anaerobes can live with or without oxygen
(1) Escherichia coli, which is common in the human digestive tract, is a
facultative anaerobe
e. Bacteria that cannot survive without oxygen are called obligate aerobes
(1) The obligate aerobe Mycobacterium tuberculosis lives in the lungs and
causes tuberculosis
8. Bacteria cause disease in 2 basic ways:
A. Bacteria can metabolize their host
1) Most bacteria secrete enzymes that breakdown organic structures so they can get their
food. This can be problematic if this is your throat or your lungs
2) Some are not lethal, just annoying. For example, the bacterium Propionibacterium acnes,
causes pimples because it metabolizes certain oils in your skin. The bacteria plug up the
pores, thus causing oil to accumulate in the skin, forming pimples and blackheads
B. Bacterial toxins
1) A toxin is a poisonous chemical
2) They can be secreted into the body of an infected person or into a food in which the
bacteria are growing
a) Clostridium botulinum causes botulism. This happens because the food was not
heated enough prior to canning, so the bacteria are still present and are able to keep
on producing their toxin
b) E. coli O157:H7 comes from undercooked meat. This bacterium releases a toxin
that causes hemorrhages of the intestines
9. How to fight bacterial illness
A. Use hot, soapy water to prevent cross-contamination between surfaces and food utensils
B. Antibiotics
1) In 1928, British bacteriologist Alexander Fleming noticed that the fungus
Penicillium, growing on an agar plate, did not allow the bacteria S. aureus to grow
near the mold
2) He concluded that the fungus must have been releasing some sort of chemical that
killed the bacteria. He isolated the substance and named it penicillin. In the 1940s,
scientists found that penicillin was very effective in treating many bacterial
infections, such as pneumonia
a) Recently, there has been a great deal of antibiotic resistance found among
populations of bacteria
3) VIRUSES CANNOT BE TREATED WITH ANTIBIOTICS!!!!
10. Bacteria are important
A. we need them in the food and chemical industry
1) Many fermented foods are made with the assistance of bacteria. Foods such as
pickles, buttermilk, cheese, sauerkraut, olives, vinegar, sourdough bread, yogurt,
etc
2) In the chemical industry, the bacterium Clostridium can make either acetone or
butanol, which are often used to make other chemicals
3) Genetic engineering companies use genetically engineered bacteria to produce their
many products, such as drugs for medicine and complex chemicals for research
4) Mining companies can use bacteria to concentrate low percentages of a desired
mineral
a) Chemoautotrophs can convert the sulfur found in these minerals into
something soluble, which can then be washed away with water, thus leaving
only the desired mineral
5) Bacteria are also useful for cleaning up environmental disasters such as petroleum
and/or chemical spills
Chapter 24 Bacteria
 Bacteria are prokaryotic single-celled organisms. They occur in several variations of three
basic shapes: rods, spheres, and spirals.
 Bacteria are the oldest and most populous organisms. They are believed to have existed on
Earth for about 3.5 billion years.
 Bacteria are classified in two kingdoms: Archaebacteria, which includes ancient forms of
life, and Eubacteria, which includes most bacteria.
 The archaebacteria include the methanogens, which produce methane gas; the extreme
halophiles, which live in very salty environments; and the thermoacidophiles, which live in
extremely acidic environments at extremely high temperatures.
 The Gram stain is used to group bacteria into two groups; Gram-positive and Gram negative
bacteria.
 The cyanobacteria are photosynthetic bacteria that probably produced much of the oxygen in
the Earth’s atmosphere.
 The major structures of the bacterial cell include a cell wall, a cell membrane, cytoplasm, a
capsule, pili, endospores, ribosomes, and movement structures.
 Aerobic and anaerobic bacteria differ in whether they need an oxygen-rich environment or
an oxygen-free environment. Different species live under different temperature conditions,
ranging from 0°C to 110°C. Most bacterial species grow best at a neutral pH.
 Genetic recombination in bacteria can occur through transformation, conjugation, and
transduction.
 Many bacteria are pathogens. Diseases may result from toxins produced by bacteria, from
the destruction of body tissues, or from bacterial enzymes interfering with normal body
processes.
 Antibiotics inhibit the growth of bacteria. Antibiotic-resistant bacteria destroy antibiotics, or
prevent entry of the antibiotic into the cytoplasm.
 Helpful bacteria are used to convert sewage into simpler organic compounds, to produce and
process food, to produce industrial chemicals, to mine for minerals, to produce insecticides,
and to clean up chemical and oil spills.
Vocabulary List
Antibiotic
Archaebacterium
Bacillus
Capsule
Chemoautotroph
Coccus
Conjugation
Conjugation
bridge
Endospore
Endotoxin
Enteric bacterium
Eubacterium
Eutrophication
Exotoxin
Extreme halophile
Facultative
anaerobe
Gram stain
Gram-negative
Gram-positive
Methanogen
Obligate aerobe
Obligate anaerobe
Pathology
Peptidoglycan
Photoautotroph
Pilus
Saprophyte
Spirillum
Staphylococcus
Streptococcus
Thermoacidophile
Thermophilic
Toxin
Transduction
Transformation