BACTERIA
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Prokaryotes are single-celled organisms that do not have a
membrane-bound nucleus.
Prokaryotes are the MOST NUMEROUS ORGANISMS ON EARTH.
Prokaryotes have evolved into many different forms, and they are
now part of nearly every environment on Earth. They have been
found at the bottom of the oceanic trenches 9.6 km (6 mi) below the
water's surface and in Arctic and Antarctic Regions.
Evidence in the fossil record indicates that Prokaryotes are about
2.5 Billion Years Old and Modern Humans arose about 100,000
years ago.
It wasn't until the late 1600s that scientists discovered bacteria. In
fact, bacteria were discovered by accident.
Anton van Leeuwenhoek accidentally noticed them while looking at
scrapings from his teeth through a very simple microscope. He did
not know what they were, but he was essentially the first person to
see bacteria.
Organisms are classified as Prokaryotes by ONE
CHARACTERISTIC: THE LACK OF A CELL NUCLEUS.
Contains two kingdoms.
Kingdom Archaebacteria
1 THE ARCHAEBACTERIA ARE A GROUP OF Prokaryotes THAT LIVE IN
UNUSUALLY HARSH ENVIRONMENTS.
2. Scientists treat Archaebacteria as a separate Kingdom because these
organisms are So Different from other Prokaryotes.
3. Archaebacteria are CHEMICALLY DISTINCT from other Prokaryotes in
several ways:
A. The Cell Walls, Cell Membranes, and Ribosomal RNA are different
from those of other BACTERIA. The Absence of PEPTIDOGLYCAN, a
protein-carbohydrate found in the cell walls of Eubacteria.
B. They can live where no other organism can survive. They live in
extreme environments, such as acidic hot springs, near undersea
volcanic vents, and highly salty water.
4. The PREFIX "ARCHEA" means ANCIENT. They are considered ancient
because they probably resemble the FIRST FORMS of LIFE on Earth.
5. Scientist think that the harsh environments in which Archaebacteria now live
are like conditions on the Earth when life first appeared and began to evolve.
Kingdom Archeabacteria
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Archaebacteria can be divided into THREE Groups, based on the
Environment in which they live:
A. METHANOGENS - Live in oxygen-free environments (anaerobic
conditions) and produce Methane Gas. They are named for their unique
method of harvesting Energy by converting H2 and CO2 into Methane Gas.
Because Oxygen is a Poison To Them, Methanogens can Live Only in
ANAEROBIC Conditions, such as the Bottom of Swamps and in
Sewage. The methane produced by methanogens living in the waters of
SWAMPS, SEWAGE, or MARSHES is called SWAMP GAS. Methane
produced in the DIGESTIVE TRACTS of many animals including humans is
called INTESTINAL GAS. In the digestive track of cows they break down
CELLULOSE, enabling cows to use nutrients in grass and plants. They are
used in INDUSTRY to treat SEWAGE and to help PURIFY WATER.
B. THERMOACIDOPHILES - Can live in Water that is Extremely HOT
(230 degrees F.) and ACIDIC (pH less than 2), two conditions that would kill
other organisms. Can be found around HOT SPRINGS like those at
Yellowstone National Park, No other organism can live in these
waters! 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.
C. EXTREME HALOPHILES - Live in Extremely SALTY
Conditions. Found in the Great Salt Lake in Utah and the Dead Sea. Can
grow in water that is up to ten times saltier than seawater. 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.
Kingdom Eubacteria
1. Eubacteria account for most bacteria; they occur in many
shapes and sizes and have distinct Biochemical and Genetic
Characteristics.
2. The PREFIX "EU" means TRUE. The so-called true bacteria
are all the organisms traditionally known as BACTERIA OR AS
MOM WOULD SAY "GERMS".
3. Bacteria can be one of THREE Different shapes; round, rod,
and spiral shaped.
4. We will be studying many different types of these kinds of
bacteria.
General Structure of Bacteria
General Structure of Bacteria
1. Nucleoid:
The nucleoid is a region of cytoplasm where the chromosomal DNA is located.
It is not a membrane bound nucleus, but simply an area of the cytoplasm
where the strands of DNA are found. Most bacteria have a single, circular
chromosome that is responsible for replication, although a few species do have
two or more. Smaller circular auxiliary DNA strands, called plasmids, are also
found in the cytoplasm
2. Cytoplasm - The cytoplasm, or protoplasm, of bacterial cells is where the
functions for cell growth, metabolism, and replication are carried out
3. Capsule - Some species of bacteria have a third protective covering, a capsule
made up of polysaccharides (complex carbohydrates). Capsules play a number
of roles, but the most important are to keep the bacterium from drying out
and to protect it from phagocytosis (engulfing) by larger microorganisms. The
capsule is a major virulence factor in the major disease-causing bacteria, such
as Escherichia coli and Streptococcus pneumoniae. Nonencapsulated
mutants of these organisms are avirulent, i.e. they don't cause disease.
4. Flagella - Flagella (singular, flagellum) are hairlike structures that provide a
means of locomotion for those bacteria that have them.
General Structure of Bacteria
5. Pili - Many species of bacteria have pili (singular, pilus), small hairlike projections
emerging from the outside cell surface. These outgrowths assist the bacteria in
attaching to other cells and surfaces, such as teeth, intestines, and rocks. Without
pili, many disease-causing bacteria lose their ability to infect because they're
unable to attach to host tissue.
6. Ribosomes- the building blocks of proteins. Proteins are the molecules
that perform all the functions of cells and living organisms
7. Cell Wall - Each bacterium is enclosed by a rigid cell wall composed of
peptidoglycan, a protein-sugar (polysaccharide) molecule. The wall
gives the cell its shape and surrounds the cytoplasmic membrane,
protecting it from its environment.
8. Cytoplasmic Membrane - A layer of phospholipids and proteins, called
the cytoplasmic membrane, encloses the interior of the bacterium,
regulating the flow of materials in and out of the cell. This is a structural
trait bacteria share with all other living cells; a barrier that allows them
to selectively interact with their environment. (this is also called cell
membrane)
Shapes of Bacteria (Eubacteria only)
Three Shapes:
1. Spirochetea/Spirilla: Spiral Shaped
- This type of bacteria is generally responsible for diseases such as
cholera ( Vibrio cholerae ), and are generally found in stagnant water, and
water which has been contaminated with sewage (this actually looks like a
curved rod).
- Basically a corkscrew shaped bacterium. It causes diseases such as
lyme disease ( Borrelia burgdorferi ).
Shapes of Bacteria (Eubacteria)
2. Bacillus or Rod-shaped
- The second and slightly more complex type of bacteria are the genus
Bacillus. These bacteria are rod shaped, and can be very short or very
long. Most bacilli are capable of forming spores, which can protect the
bacteria from harsh conditions such as dryness etc, and the bacteria
within can remain viable for up to 100 years.
- Bacilli are also capable of causing many diseases, such as Yersinia
pestis, which causes bubonic, pneumonic and sceptacaemic plague, and
Bacillus anthracis, which causes the, by now probably very famous
disease, due to the post 9/11 attacks, anthrax. Common types of bacillus
are Lactobacillus spp which generally cause milk to spoil, and a number
of various soil dwelling species.
Salmonella
typhi
Shapes of Bacteria (Eubacteria)
3. Cocci or round shaped:
- These bacteria are generally some of the smallest, and simplest, being
small and spherical, hence Cocci (berry shaped).
- There are a number of bacteria in this category which are pathogenic
(disease causing) such as Staphlycoccus aureus , which causes a type of
food poisoning, and is rapidly becoming known as the hospital superbug,
a variant of this species called MRSA (Methicillin Resistant Staphylococcus
aureus ), N. meningitidis, which causes the often deadly diseases,
meningitis, Staphylococcus epidermis which inhabits the skin and can
cause spots and boils, and finally Moraxella catarrhalis, which generally
tends to cause infections in the lower respiratory tract in humans.
pair of Cocci
Staphylococcus
aureus
Bacteria exists in groups and colonies
A. Strepto: chains of bacteria
Streptococcus
Groups of Bacteria
B. Staphylo: Clusters
Staphylococcus
Groupings of bacteria
C. Diplo: two
Diplococcus
Bacterial groups
D. Tetra: Four
A tetrad appears
as a square of four
cocci (arrows).
Tetracoccus
Gram Staining
Most species of bacteria can be grouped into TWO Categories based on their
response to a laboratory technique called GRAM STAINING. (Figure 23-4)
1. TAXONOMISTS divide bacteria into various subgroups including GRAMPOSITIVE AND GRAM-NEGATIVE BACTERIA.
2. Hans Christian Gram, a Danish Microbiologist, developed the Gram-stain
technique in 1884
3. The technique involves STAINING Bacteria with a PURPLE DYE (Crystal
Violet), AND IODINE, AND RINSED WITH ALCOHOL. Then Restained
with A PINK DYE (Safarinin). (Figure 24-3)
4. Depending on Structure of their CELL WALLS, THE BACTERIA ABSORB
EITHER THE PURPLE DYE OR THE PINK DYE.
5. Gram-Positive Bacteria will retain the PURPLE DYE and appear
Purple.
6. Gram-Negative Bacteria will appear PINK from the PINK DYE.
Gram Positive Bacteria: antibiotics can work
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1. GRAM-POSITIVE BACTERIA HAVE A THICKER LAYER OF
PEPTIDOGLYCAN IN THEIR CELL WALLS, MADE OF A PROTEINSUGAR COMPLEX THAT TAKES ON THE PURPLE COLOR DURING
GRAM STAINING
2. Gram-positive bacteria include organisms that produce BENEFICAL
Substances and organisms that cause important DISEASE.
3. They are used to make yogurt, pickles and buttermilk.
4. Another group of Gram-positive bacteria, are used to make ANTIBIOTICS,
INCLUDING TETRACYCLINE AND STREPTOMYCIN. THESE
BACTERIA ARE CALLED ACTINOMYCETES.
5. Antibiotics kill other Gram-positive bacteria by preventing them from making
proteins. They affect only the GROWTH of bacteria without harming the body
cells of humans.
6. Gram-positive bacteria cause many HUMAN DISEASES, INCLUDING
SCARLET FEVER, TOXIC SHOCK SYNDROME, AND PNEUMONIA.
7. Many of these bacteria produce TOXINS, which are poisons to our bodies.
8. Toxins can be deadly; a single gram of the toxin produced by Clostridium
botulinum (Botulism) could kill more than one million people.
Gram-negative bacteria: antibiotics cannot work
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1. GRAM-NEGATIVE BACTERIA HAVE AN EXTRA LAYER OF
LIPID ON THE OUTSIDE OF THE CELL WALL AND APPEAR PINK
AFTER GRAM STAINING.
2. The extra lipid layer stops the PURPLE Stain from entering the CELL
WALL. They do absorb the PINK Stain, so they are easily distinguished with
a microscope.
3. The extra lipid layer also stops many ANTIBIOTICS from entering the
bacteria. Treatment for these requires a different ANTIBIOTIC than those
used for infections caused by Gram-positive bacteria.
Bacterial Reproduction
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Bacteria can reproduce at tremendous speeds. Some bacteria can
reproduce as often as once every 20 minutes! However, bacteria have
to have certain conditions in which to reproduce. These conditions are
not often met, and that is one thing that keeps bacteria from growing
out of control.
Bacteria reproduce using two basic methods: asexual reproduction
and sexual reproduction.
Asexual reproduction involves only one individual or parent. The
offspring generated by asexual reproduction are exact duplicates of the
parent. Binary fission is the process by which a bacteria splits into
two cells. Each cell gets an exact copy of the parent cell's genetic
material.
Binary Fission
Reproduction
Sexual reproduction involves the joining of two
parent cells and the exchanging of genetic
materials. In sexual reproduction, the offspring
will have a mixture of the parent cells'
traits. Conjugation is the process by which
bacteria join and exchange genetic
materials. Once genetic materials are
exchanged, each bacteria cell will go through
binary fission to produce an offspring with a new
genetic makeup.
Additional Vocabulary
1.
2.
3.
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5.
Aerobic: needs oxygen
Anaerobic: without oxygen
Faculatice Anaerobic: with or without oxygen
Autotrophs: Make own food
a. Photoautotroph: Use sunlight to make food
b. Chemoautotrophs: Use energy of chemical reactions
for food
Heterotrophs: Get food from another source
a. Saprophyte: feeds on dead decaying matter