Download Chapter 24-Bacteria

Chapter 24: Bacteria
24-1 Bacterial Evolution and Classification
24-2 Biology of Bacteria
24-3 Bacteria and Humans
24-1 Bacteria Evolution and Classification
I. Evolution (~ 1 billion years BEFORE eukaryotes)
• Microscopic prokaryotes  WIDEST range of HABITATS
(i.e., OLDEST living cells).
Critical Thinking
(1) Biologists have only recently discovered fossilized bacteria. Suggest a
reason as to why this discovery may have taken so long.
(A) Classification (Kingdom Archaebacteria, Kingdom Eubacteria)
• Based on STRUCTURE, reactivity to STAINS, and DNA SEQUENCE.
(1) Eubacteria (Kingdom Eubacteria)
• More RECENTLY evolved and DIVERSIFIED kingdom of bacteria.
(2) Archaebacteria (Kingdom Archaebacteria)
• FIRST living CELLS to SHARE some GENES SIMILAR to EUKARYOTES.
Critical Thinking
(2) Microbiologists consider archaebacteria to be a good model of lifeforms that may exist on other planets. Why do you believe these species
were selected as models?
II. Kingdom Archaebacteria (Ancient Bacteria)
• Classified by GENETIC and HABITAT differences, 3 Classes.
(1) Peptidoglycan (an evolved structural component)
• Carbohydrate in CELL WALL of EUBACTERIA, but is ABSENT in
archaebacteria.
(2) Methanogens (swamps—marsh gas, sewage, intestinal tracts of humans)
• Anaerobic that convert H2 and CO2 into METHANE gas (CH4)
(3) Extreme halophiles (Great Salt Lake, Dead Sea)
• SALT-loving that convert SALTS into ATP.
(4) Thermoacidophiles (Geothermal Vents, Hot Springs)
• Inhabiting ACIDIC (pH < 2) and HOT habitats (up to 230 o F);
(Several species known to be CHEMOSYNTHETIC).
Critical Thinking
(3) Thermal vent communities, which are extremely hot regions of ocean in
areas where the Earth’s crust is open, have some of the densest and most
productive populations known to exist. What might explain this?
III. Kingdom Eubacteria (estimated to be 90% of ALL bacteria)
• Structured as 1 of 3 SHAPES.
(1) Bacillus (Bacilli)
• ROD-shaped eubacterium (e.g., Anthraxis bacillus).
(2) Coccus (Cocci)
• SPHERICAL-shaped eubacterium (e.g., Streptococcus pyrogenes)
(3) Spirillum (Spirochete)
• SPIRAL-shaped eubacterium (e.g., syphilis)
(4) Streptococcus
• Coccus eubacteria in CHAINS.
(5) Staphylococcus
• Coccus eubacteria in CLUSTERS.
(A) Gram Stain (Danish physician, Hans Christian Gram)
• Most eubacteria are grouped into TWO categories based on “Gram Stain.”
(1) Application of crystal violet to microscope slide
(2) Application of iodine to microscope slide
(3) Alcohol wash of microscope slide
(4) Application of safranin to microscope slide
NOTE: In addition to the staining, G + and G - ALSO have
(1) Different susceptibilities to ANTIBIOTICS,
(2) Produce different types of TOXINS, and
(3) React differently to DISINFECTANTS
(1) Gram-positive (G+) eubacteria
• RETAIN stain due to THICKER layer of peptidoglycan in CELL WALL
and thus appear PURPLE.
(2) Gram-negative (G-) eubacteria
• FAIL to retain stain due to a THINNER layer of peptidoglycan and
appear PINK (from the safranin)
(B) Phylum Cyanobacteria (photosynthetic eubacteria)
• By releasing O2 as a WASTE, they created a way for both TERRESTRIAL
life (ozone) and AEROBIC life-forms.
(1) Heterocysts (in cyanobacteria)
• Specialized CELLS contain ENZYMES which can FIX N2 for plants.
(2) Eutrophication (Population Bloom)
• Sudden INCREASE in cyanobacteria due to a lot of nutrients.
(i.e., PO4 and nitrates, decomposed by heterotrophic bacteria)
(C) Phylum Spirochetes (majority are pathogenic and G-)
• Inhabit aerobic AND anaerobic habitats and MOVE via a corkscrew-like
rotation
(e.g., Treponema pallidum, a spirochete  causes syphilis).
(D) Phylum Gram-Positive (G+) Bacteria
• Strep throat, turn milk to YOGURT, protect AGAINST pathogens in
mouth and intestine, BUT cause TOOTH decay from ACID secretion.
(1) Actinomycetes (a proven ARMS factory)
• Class of G + bacteria that form BRANCHING FILAMENTS in SOIL and
make ANTIBIOTICS.
(2) Antibiotics (anti-microbial weapons)
• Substances that INHIBIT the GROWTH or KILL microbes.
(E) Phylum Proteobacteria (G -)
• Large phylum; ENTERIC, CHEMOAUTOTROPHIC, and N-Fixing bacteria.
(1) Enteric bacteria (G-, aerobic or anaerobic, include E. coli)
• Inhabit INTESTINAL tracts (make vitamin K, assist with digestion), BUT
also Salmonella, ~ FOOD poisoning.
(2) Chemoautotroph (G-, aerobic or anaerobic)
• Extract NRG from compounds to make CARBOHYRDATES.
(e.g., Fe-oxidizing bacteria in freshwater ponds, Rhizobium, a N-fixing
bacteria that lives symbiotically with legumes).
24-2 Biology of Bacteria
I. Bacterial Structure (BEYOND light microscopy)
• Structures evolved with ADAPTATIONS to serve various niches.
(A) Cell Wall (peptidoglycan ~ BACTERIA, cellulose ~ PLANTS)
• In G - bacteria, CELL WALL includes an OUTER lipid bilayer.
(NOTE: Several antibiotics have LITTLE to NO effect on G – bacteria).
Critical Thinking
(4) Penicillin works by interfering with the ability of bacteria to polymerize
the peptidoglycan cell wall. Given this fact, explain why Gram-positive
bacteria are more susceptible to the effects of penicillin than are Gramnegative bacteria.
(B) Cell Membrane (lipid bilayer) and Cytoplasm
• NO mitochondria,  CELL MEMBRANE creates a H+ gradient to drive
cellular RESPIRATION.
NOTE: PHOTOSYNTHETIC bacteria have membrane FOLDINGS called
THYLAKOIDS, similar to chloroplasts.
(C) Capsules and Pili (part of CELL WALL)
• Adaptations used for ATTACHMENT and GENETIC recombination.
(1) Capsule (OUTER polysaccharide shell)
• Protects AGAINST desiccation, chemicals, and WBC attack.
(2) Glycocalyx (a sticky SUGAR COAT on OUTER capsule)
• Enables bacteria to ATTACH to surface of HOST cells.
(3) Pilus (“pili” on bacterial SURFACE)
• Short, hair-like proteins used to ADHERE to host cells AND for
transferring DNA between bacteria.
(D) Endospore (develops when HARSH abiotic forces predict cell death)
• DORMANT structure surrounds bacterial DNA for protection.
NOTE: When conditions become MORE favorable, the endospore will
OPEN, allowing bacterium to EMERGE and begin multiplying.
Critical Thinking
(5) Disease-causing bacterial cells usually die in boiling water within a
FEW minutes. Why then, do hospitals sterilize surgical instruments by
exposing them to steam and pressure for at least FIFTEEN minutes?
(E) Movement Structures (THREE methods)
• FLAGELLA—singular OR clustered, SLIME—secreted to glide upon via
wavelike contractions, CORKSCREW-Rotation—spiraled movement.
NOTE: MOTILE bacteria require FLEXIBLE cell walls and filaments within
cell walls that contract, allowing bacterium to bend and move.
II. Nutrition and Growth (~ by O2, Temperature, pH, and Sunlight)
• Either heterotrophic OR autotrophic depending on METABOLISM.
(1) Saprophytes (decomposers, SAPROPHYTIC)
• Heterotrophic bacteria that feed on DEAD and DECAYING biomass.
(2) Photoautotrophs (e.g., producers like cyanobacteria)
• Use SOLAR NRG to MAKE organic compounds.
NOTE: Chemoautotrophs, including Nitrosomonas, oxidize ammonia
(NH3) to form nitrite, and harvest the resulting NRG.
Critical Thinking
(6) Clostridium tetani, the bacterium that causes tetanus, is an obligate
anaerobe. From this data, would you infer that a deep puncture wound or
a surface cut would be more likely to become infected by tetanus
bacteria? Explain your reasoning.
(3) Obligate Anaerobes (obligatory anaerobes)
• Bacteria that CANNOT survive in the presence of O2. (e.g., Clostridium
tetani)
(4) Facultative Anaerobes (adaptable anaerobes)
• Bacteria that CAN live with OR without presence of O2. (e.g., E. coli)
(5) Obligate Aerobes (obligatory aerobes)
• Bacteria that REQUIRE the presence of O2 to live.
(e.g., Mycobacterium tuberculosis)
(6) Thermophilic bacteria
• Populate the FASTEST in environments between 104-230 o F
III. Genetic Recombination (i.e., NOT reproduction, no NEW cells made)
• 3 ASEXUAL methods to acquire AND express new combinations of DNA
(in PLASMID form).
(1) Transformation (Frederick Griffith’s Experiment)
• Occurs when a bacterium TAKES IN foreign DNA and ACCEPTS IT.
(2) Conjugation (leads to a “conjugation bridge”)
• 2 bacteria BIND together WHILE one transfers DNA to the OTHER.
(NOTE: Requires donor plasmid & pilus)
(3) Conjugation Bridge (a specialized pilus)
• A PASSAGEWAY for transfer of DNA between TWO bacteria
(NOTE: Bridge detaches AFTER transfer is complete).
(4) Transduction (used in genetic engineering)
• Transfer of DNA through a VIRAL vector (i.e., a bacteriophage).
24-3 Bacteria and Humans
I. Bacteria and Humans
• Pathogenic, BUT RECYCLERS, used for FOOD, and Genetic Engineering.
Critical Thinking
(7) Do you believe it would be safe to eat potato salad that was made with
homemade mayonnaise and left unrefrigerated? Explain why or why not.
(1) Pathology (pathogens are DISEASE-causing agents)
• Branch that studies INFECTIOUS disease and TOXINS.
Critical Thinking
(8) When a physician treats a patient for a bacterial infection, antibiotics
are prescribed at a regulated dose for several days, instead of a megadose
in one or two days. Why do you suppose a physician would do this?
(Note: Bacterial endotoxins are released when a bacterium dies)
(2) Exotoxins (protein-based, G+ bacteria)
• Poisons STEADILY released from LIVING G + bacteria.
(e.g., Tetanus and Botulism both result from exotoxins)
(3) Endotoxins (glycolipid-based, G - bacteria)
• Poison released from OUTER membrane of DEAD G – bacteria.
NOTE: In addition to TOXINS, bacteria adhere to cells AND secrete
digestive ENZYMES that destroy body tissues.
Critical Thinking
(9) Examine the photographs below of bacteria that have been treated
with Gram staining. Would you hypothesize that either of these bacteria
manufacture endotoxins? Explain your response.
(A) Antibiotics
• Drugs derived from BACTERIA and FUNGUS  Fight bacteria by
INTERFERING with bacterial functions.
Critical Thinking
(10) Over the last twenty years, the number of antibiotic-resistant
bacterial pathogens has steadily increased. This is believed to be a
result of antibiotic abuse by patients and doctors. Doctors tend to
overprescribe antibiotics for patients who demand a quick fix for their
illness. Just recently, the World Health Organization (WHO) has
established a database so that doctors can report outbreaks of
antibiotic resistance. What do you suppose may be one of the potential
benefits of such a database?
(1) Penicillin
• Interferes with CELL WALL synthesis.
(2) Tetracycline
• Interferes with PROTEIN synthesis.
(3) Sulfa Drugs (NEW and ARTIFICIAL)
• Antibiotics MADE in laboratories (NOT naturally occurring).
(4) Broad-Spectrum Antibiotics (the BIG guns)
• Affect a WIDE RANGE of bacteria; (valuable, BUT with OVERUSE, they
LOSE their effectiveness).
(B) Antibiotic Resistance
• Bacteria MOST susceptible die FIRST; however, a few MUTANT
resistant bacteria SURVIVE and continue to grow with RESISTANCE.
NOTE: Bacterial DEFENSES include cell walls that PREVENT passage of
the antibiotic as well as secretion of bacterial ENZYMES that destroy or
alter the antibiotic, REDUCING its effectiveness.
Critical Thinking
(11) Some of the bacteria that are normally found in the human intestinal
tract are beneficial. For example, E. coli produces vitamin K. However, E.
coli an also cause diarrhea under exceptional circumstances, and it can
cause serious infections if it invades other parts of the body. OTHER
bacteria found in the digestive tract do NOT produce substances the body
can use, BUT they do NOT produces substances that are harmful either.
Suggest a positive role you feel these bacteria might play.
II. Useful Bacteria
• ECOLOGICAL roles as decomposers (recently, with oil spills), N-fixers,
photosynthetic producers.
FOOD: Bacteria ferment the lactose in milk to produce buttermilk, sour
cream, and yogurt… others digest the proteins in milk and produce
unripened cheeses including ricotta and cottage cheese.
• Also…sauerkraut (digested cabbage) and pickles (fermented cucumbers)
Revisiting Cell Structure and Function
• Focus on the relationship between bacterial structures and
functions, such as the cell wall and flagella.
Assessing Prior Knowledge
• Distinguish between prokaryotic cells and eukaryotic cells.
• List two metabolic pathways that cells use to harvest energy from
nutrients.
• To what kingdoms do bacteria belong?