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Bacteria
singular: bacterium / plural: bacteria
1. Bacteria are classified into two kingdoms: Eubacteria (true bacteria) and Archaebacteria (Ancient
Bacteria).
2. BACTERIA are microscopic Prokaryotes. (“before nucleus”)
3. Adapted to living in all environments (even some extreme) – they exist EVERYWHERE
I. Bacterial Structure
1. Outside the plasma membrane of most cells is a rigid cell wall made of peptidoglycan
a. The cell wall may be surrounded by an organized capsule called a glycocalyx and/or by a loose gelatinous sheath
called a slime layer.
b. In parasitic forms, these outer coverings protect the cell from host defenses.
2. Some prokaryotes move by means of flagella, capable of 360o rotation which causes the cell to spin and move forward.
3. Many prokaryotes adhere to surfaces by means of fimbriae, hairlike filaments extending from the surface. (gonorrhea,
tooth decay)
4. Prokaryotic cells lack the membranous organelles of eukaryotic cells (and no membrane bound nucleus).
5. A nucleoid is a dense area in prokaryotes where the chromosome is located; it is a single circular strand of DNA.
6. Plasmids are accessory rings of DNA found in some prokaryotes; they can be extracted and used as vectors to carry
foreign DNA into bacteria during genetic engineering procedures.
7. Protein synthesis in prokaryotic cells is carried out by thousands of ribosomes, which are smaller than eukaryotic
ribosomes.
II. Reproduction in Prokaryotes
Binary fission is the splitting of a parent cell into two daughter cells; it is asexual
reproduction in prokaryotes.
In bacteria, genetic recombination can occur in three ways.
a. Conjugation occurs when a bacterium passes DNA to a second bacterium through a tube
(sex pilus) that temporarily joins two cells; this occurs only between bacteria in the same
or closely related species.
b. Transformation involves bacteria taking up free pieces of DNA secreted by live bacteria or
released by dead bacteria.
c. In transduction, bacteriophages transfer portions of bacterial DNA from one cell to another.
d. Plasmids can carry genes for resistance to antibiotics and transfer them between bacteria by any of these processes.
Some bacteria form resistant endospores in response to unfavorable environmental conditions.
.
III. Prokaryotic Nutrition
1. Bacteria differ in their need for, and tolerance of, oxygen (O 2).
a. Obligate anaerobes are unable to grow in the presence of O2; this includes anaerobic bacteria that cause botulism,
gas gangrene, and tetanus.
b. Facultative anaerobes are able to grow in either the presence or absence of gaseous O 2.
c. Aerobic organisms (including animals and most prokaryotes) require a constant supply of O 2 to carry out cellular
respiration.
2. Autotrophic Prokaryotes
a. Photoautotrophs are photosynthetic and use light energy to assemble the organic molecules they require.
b. Chemoautotrophs make organic molecules by using energy derived from the oxidation of inorganic compounds in
the environment. (methanogens)
3. Heterotrophic Prokaryotes
a. Most free-living bacteria are chemoheterotrophs that take in pre-formed organic nutrients.
b. As aerobic saprotrophs, there is probably no natural organic molecule that cannot be broken down by some
prokaryotic species.
c. Detritivores (saprophytic bacteria) are critical in recycling materials in the ecosystem; they decompose dead organic
matter and make it available to photosynthesizers.
IV. Bacterial Diseases in Humans
a.
b.
c.
Microbes that cause disease are called pathogens.
Pathogens may be able to produce a toxin, and or adhere to surfaces and sometimes invade organs or
cells.
-Toxins are small organic molecules that are released when bacteria die.
-In almost all cases, the growth of the bacteria does not cause disease but instead the toxins they
release cause the disease. Example: Clostridium tetani, the causative agent of tetanus.
capsules (slime layers) - help evade immune system and adhere to surfaces
V BACTERIA CLASSIFICATION
1. The Gram stain procedure (developed in the late 1880s by Hans Christian Gram) differentiates bacteria.
a. Gram-positive bacteria stain purple, whereas Gram-negative bacteria stain pink.
b. This difference is dependent on the thick or thin (respectively) peptidoglycan cell wall.
2. Bacteria have three basic shapes.
a. A spirillum is spiral-shaped.
b. A bacillus is an elongated or rod-shaped bacteria.
c. Coccus bacteria are spherical.
.
How Gram Stains are Made
Not all bacteria can
be stained by
Gram's method,
the best-known
exception belong
to the genus
Mycobacterium
which have waxy
cell walls.
VI. Bacteria and Health -
For more information on Gram Stains,
see
http://wwwmicro.msb.le.ac.uk/video/Gram.html
Tetanus | botulism | Black Plague | Tuberculosis | gonorrhea | syphilis | Lyme disease | Strep throat |
Pneumonia | Anthrax | necrotizing fasciitis (flesh eating bacteria) | toxic shock syndrome
The Usual Suspects
*these are specific bacteria you need to know for the test (see microslide lab)
Streptococcus lactis
strep throat, related bacteria causes necrotizing fasciitis
Staphylococcus aureas
found on skin, responsible for minor infections (like on cuts/scratches)
Bacillus subtilis
common lab bacteria, easy to grown, unharmful
Bacillus (Clostridium)tetani
causes tetanus (lockjaw)
Clostridium botulism
causes botulism (food poisoning)
Bacillus (Yersinia) pestis
causes Black Plague
Bacillus anthracis
anthrax
Mycoplasmas
very very tiny, cause of pneumonia
Rickettsia rickettsi
link between bacteria and viruses, can't reproduce outside host, causes Rocky Mountain Spotted Fever
Escherichia coli
E. Coli - common bacteria of the digestive tract, also causes food poisoning
Antibiotics and Antiseptics
Joseph Lister created the first antiseptic, an acid to spray on tables and instruments before surgery (1860)
The Discovery of Penicillin by Alexander Fleming
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Alexander Fleming
Noticed mold growing on petri dishes
Bacteria did not grow where the mold was
He isolated the chemical that killed bacteria, but it was not stable
Howard Flory continued the work, later stabilized the chemical
Fleming and Flory received the Nobel Prize in 1945