Bacteria Notes
Classifying Bacteria:
Bacteria, at one time, were grouped into one kingdom- Kingdom Monera. With new technology, scientists started looking at the DNA of organisms. Scientists found that there are large differences in the DNA sequences of two groups of bacteria. Scientist now separates these two groups into two kingdoms:
1.
Kingdom Archaebacteria-
“ancient” bacteria are found in extreme environments that do not contain
oxygen.
Methanogens are examples that produce methane. They can be found in swamps (swamp gas) and in the intestines of cows. In cows, these bacteria help break down the cellulose in plant cell walls.
2.
Kingdom Eubacteria- “true” bacteria are
found everywhere because of their diversity in the kind of metabolism they
can have.
Structure:
q All Bacteria are unicellular (one-celled).
q All Bacteria are prokaryotic (no nucleus).
q The typical bacteria is 1/30 the size of our
cells.
q Bacteria have one circular chromosome called a plasmid.
q The DNA is not contained in a nucleus, but floats
around the cytoplasm.
q Most bacteria have a cell wall called a capsule,
which protects it from injury and osmotic (water) pressure.
q Bacteria have a cell membrane.
q Bacteria do not have membrane-bound organelles. They do contain ribosomes that
produce needed enzymes.
q Some bacteria have pilli that help bacteria
stick to each other and to surfaces.
q Some bacteria have whip-like flagella that aid
in movement.
Movement:
Bacteria
can move by tumbling, secreting slime, or by using flagella to move it
forward. Only a few forms are unable to
move.
The Cell Wall:
A
Danish physician named Christian Gram was the first to develop a simple
way of identifying bacteria groups by observing the cell wall. He used crystal violet, a purple stain to
dye the bacteria so that he could see them better under the microscope. What did he see?
He saw that some bacteria absorbed
the stain and looked purple.
Other bacteria did not absorb the stain and looked pink. To this day his technique, now called Gram
staining, is used to identify the type of bacteria.
q Gram-positive bacteria are bacteria that absorb the stain and look purple
under the microscope.
q Gram-negative bacteria are bacteria that do not absorb the stain and look
pink. Why did gram negative not absorb
the stain? It is because these
bacteria have a third lipid layer that repels the stain. These bacteria are more resistant to
antibodies because of this protective layer.
q Penicillin
is an antibiotic that works well on Gram- positive bacteria but does not
work well on gram-negative bacteria.
Shape:
Under
the microscope, bacteria can be described and identified by observing their
shape:
There are three basic shapes:
-rod shaped -sherical
shaped -spiral shaped
Singular (bacillus, coccus,
spirillum)
Bacteria
usually do not exist alone. They are
clumped together in groups. These
groups can be observed under the microscope.
The following prefixes can be added to describe these groupings:
Diplo- 2 linked Strepto- long chains Staphylo –clumps
Growth:
q Bacteria can reproduce fast. They can reproduce every 15 to 20 minutes. With ideal conditions, they could easily
over-populate the world.
q There are limiting factors that control the
bacteria population: amount of food, water, space, and temperature.
q Bacterial growth is an example of exponential
growth, which means that with each generation the amount of individuals
born is doubled. Example
(1,2,4,8,16,32,64,128,256, 512,1024…) In one day’s time, one bacterium can
produce 4 billion bacterial cells.
Reproduction:
Bacteria
can reproduce in three ways:
q Binary
fission – asexual
reproduction in which a bacterium doubles in size, replicates its one
chromosome, and divides in half producing two identical daughter cells.
q Conjugation- a
few species can undergo sexual reproduction. This involves a bridge (pilli) between two bacteria, through
which some DNA is transferred from one cell to another. This form of reproduction ensures that some
bacteria will have the right combinations of genes to evolve and adapt
to changing environments. (E-coli)
q Forming endospores- many bacteria can form endospores to protect
them from harsh condition. When
conditions get bad, a thick walled spore form inside the bacteria. It is resistant to heat, drying,
radiation, and even chemical disinfectants. Some can come back to life after thousands of years.
How Bacteria Obtain Energy:
q Some
bacteria are heterotrophs, meaning they cannot make their own food.
§
Saphrophytes- Decomposers /recycle nutrients
back to the soil
§
Parasites- feeding and harming a living
host
§
Symbiotic/mutualism- both organisms
benefit. (E-coli in intestines)
q Some
bacteria are autotrophs, meaning they can make their own food.
§
Photosynthetic bacteria use energy from the sun
to make food.
§
Chemosynthetic bacteria use heat and chemicals
like ammonia, sulfur, iron, or hydrogen for food.
Oxygen and Bacteria Metabolism:
q Some
bacteria use oxygen to break down food and are called aerobes.
q Some
bacteria use oxygen to break down food, but can switch to fermentation when
oxygen is not available. These bacteria
are called Facultative anaerobes.
q Some
bacteria do not use oxygen to break down food and are called anaerobes. Oxygen can kill these bacteria.
§
All archaebacteria are anaerobes.
§
Anaerobic eubacteria are responsible for many diseases like tetanus,
gas gangrene, and botulism. Botulism is a cause of food poisoning.
q Decomposers and recyclers- most important decomposers on Earth
q Symbiotic relationships- E-coli helps digest food and make a number of
vitamins like Vitamin K and some B vitamins.
q Nitrogen fixation- bacteria can turn nitrogen gas into nitrates for plants to use.
q Food processing- bacteria are used to make yogurt, cheese, buttermilk, pickles,
sauerkraut, vinegar, etc.
q Sewage Treatment- tons of bacteria are added to sewage to break down human waste, food,
and chemicals.
q Mining- bacteria
are used in mining copper.
q Genetic Engineering- bacteria with human genes inserted into them (plasmids)
produce proteins like human growth hormone and insulin (for diabetics)
Bacteria
can cause the following diseases: Strep
throat, diphtheria, tuberculosis, typhoid fever, tetanus, syphilis, gonorrhea,
cholera, Lyme disease, and bubonic plague.
Bacteria can cause disease by two ways:
q Attack cells and tissue directly, digesting
them as food.
q Release toxins (poisons) that travel through out the body interfering with normal
functions.
q Botulism and Salmonella are both causes of food poisoning that produce
toxins. Botulism comes from improper
canning. Salmonella comes from improper
cooking of meats and eggs.
Bacteria can be controlled
by:
§
Vaccines -- before infection (mostly for viruses)
§
Antibiotics -- after infection
§
Sterilization -- using heat and pressure (destroys endospores)
§
Disinfectants -- chemicals that kill bacteria but not endospores.
§
Wash Hands! Clean countertops
before cooking!
§
Cooking food
properly -- correct temperature and
length of cooking time.
§
Proper canning
techniques—no dints and good seals
in cans and jars.
§
Treating foods with preservatives—discourages
growth
§
Irradiation of foods -- using radiation to kill bacteria
§
Refrigeration -- does not kill bacteria but slows down growth.
Antibiotic Usage:
Antibiotics were first used during
WWII and helped win that war. In
the 1940’s penicillin became widespread and was used for
everything. People were given
antibiotics before surgery; they were given to cattle to keep them healthy; and
prescribed for minor infections.
This widespread use has caused the evolution some bacteria into “super
bugs” which are bacteria that are immune to at least five or more
antibiotics.
1/3 of the Salmonella
bacteria today are drug-resistant.
Several strains of tuberculosis causing bacteria are resistant to
every antibiotic currently in use.
What can be done? --education and new treatment
strategies. If antibiotics were not
taken as directed, not all of the bacteria would die. Some antibiotic resistant forms may live and reproduce.