Transcript Ch 27 Lecture

Chapter 27~
Prokaryotes
and the
Origins of
Metabolic
Diversity
I.
Phylogeny of Prokaryotes
A. More prokaryotes inhabit a handful
of fertile soil or the mouth or skin of
a human than the total number of
people who have ever lived.
1. No membrane bound organelles
2. Single celled
3. Classified by nutritional class and reactivity to
oxygen
4. Not by Phyla/Divisions, but by Strains
5. Heterotrophs or Autotrophs
(photoautotrophs or chemoautotrophs)
B. Kingdom:
Monera?
Some books
suggest two
Domains:
1. Archaebacteria
“ancient”
2. Eubacteria
“true”
C. Three domain system
1. Prokaryotes split early in the history of living
things
2. Archaea are more closely related to Eukarya
than bacteria
3. Eukarya are not directly related to Eubacteria
1. Archaebacteria
Live in extreme
environments
“extremophiles”
A. Halophiles- salt
lovers
B. Methanogens –
produce methane
as a by-product
C. Thermoacidophiles
- love hot, acidic
places
2. Eubacteria
Classified
according to
their mode of
getting
nutrients,
mechanism of
movement, and
their shape
D. Extreme thermophiles thrive in
hot environments.
1. The optimum temperatures for most
thermophiles are 60oC-80oC
Sulfolobus oxidizes sulfur in hot
sulfur springs
in Yellowstone
National Park
Photo taken by Mrs. Brown!
1.
2.
3.
4.
5.
Most
prokaryotes
are bacteria
II. Structural characteristics
A. Shape
1. cocci (sphere)
2. bacilli (rod)
3. helical (spiral)
B. Cell wall: peptidoglycan (sugars &
proteins)
Gram +: with
peptidoglycan
Gram - : little
peptidoglycan;
impede drug
action ; most pathogens
 Gram-positive bacteria have cell walls
that are up to 10 times thicker than
gram-negative bacteria.
“Gram” named after Hans Christian Gram
who first came up with a method of
staining bacteria.
Gram-positive = stains bright purple
Gram-negative = no stain (light pink)
Gram-Positive:
Staphylococcus epidermidis,
Streptococcus pyogenes,
Clostridium tetani
Gram-Negative:
Escherichia coli,
Salmonella typhi,
Vibrio cholerae
C. Capsule: adherence to substrate,
causes tooth decay; protection
from drying out & attack from
immune system
D. Pili: short, straight hair-like
appendage; attachment to other
bacteria
Streptococcus mutans. The bacteria adhere to the surface of the tooth
and then grow and synthesize a polysaccharide capsule which binds
them to the enamel and forms a biofilm 300-500 microbial cells in
thickness. The bacteria convert sugars in the diet into the dextran that
forms plaque and cements the bacteria to tooth enamel. Within the
plaque the bacteria convert sugars to lactic acid which can lead to
dental caries or bacterial infection of the tooth.
III. Motility
A. Flagella –
primary
function
= locomotion
propels bacterium in straight line
B. Filaments- found in spirochetes
(helical shape) move through viscous
liquid like a corkscrew (syphilis in mouth
or genitals)
Salmonella enterica
Spirochete:
Treponema pallidum
C. Slime gliding- secretion of slimy
threads
D. Taxis- seek out favorable
environments and avoid harmful
ones
1. Chemotaxis- movement toward
nutrients, away from toxins
2. Phototaxis- move or swim toward
light
3. Magnetotaxis- move along magnetic
flux lines
IV. Form & Function
A. Prokaryotes have smaller, simpler
genomes than eukaryotes (about 0.001)
B. Nucleoid region or genophore: noneukaryotic chromosome
1. Double-stranded DNA in the form of a ring
C. Plasmids- smaller
ring of DNA
1. provide genes for
resistance to antibiotics
2. metabolism of
unusual nutrients
3. Replicate
independently of chromosome
V. Growth, Reproduction and
Genetic Exchange
A. Asexual reproduction:
binary fission (not mitosis)
1. Single cell produces a colony of
offspring
B. “Sexual” reproduction or combining
genes (not meiosis):
1. Transformation: uptake of genes from
surrounding environment
2. Conjugation: direct gene transfer from
1 prokaryote to another
3. Transduction: gene transfer by viruses
C. Mutation is major source of genetic
variation  able to adapt to
environment because generations
made within hours  constant
changes
D. Endospore Formation- withstand harsh
conditions
1. Structure that withstands high heat, radiation,
desiccation, toxins
2. Survival for hundreds of years
3. Form during unfavorable conditions
4. Low in water content (15% vs. 90%)
5. Thick, tough wall
forms
6. When environment is
hospitable, absorbs
water and grows
Parts of the Spore
1. Core - The core is dehydrated cytoplasm containing DNA,
ribosomes, enzymes etc. Everything that is needed to function
once returned to the vegetative state.
2. Cortex - The cortex is a modified cell wall/peptidoglycan layer that
is not as cross-linked as in a vegetative cell.
3. Coats - Outside of the cortex are several protein layers that are
impermeable to most chemicals. The coat is responsible for the
spores resistance to chemicals
VI. Nutrition & Metabolism
A. Four major groups based on source of
carbon and energy
1. Photoautotrophs- CO2 and light
2. Chemoautotrophs- CO2 + inorganic molecules
(oxidize H2, H2S, NH3, Fe++)
3. Photoheterotrophs- organic molecules and
light
4. Chemoheterotrophs- organic molecules
A. Saprobes- decomposers, absorb nutrients
from dead organisms
B. Parasites- from the body fluids of living hosts
B. Prokaryotes play an important role,
responsible for key steps in the cycling
of nitrogen (essential to proteins and
nucleic acids) through environments.
1. Some bacteria convert ammonium (NH4+)
to nitrite (NO2-)
2. Others “denitrify” nitrite or nitrate (NO3-)
to N2, returning N2 gas to the atmosphere
3. Some (ex. Cyanobacteria) can use
atmospheric N2 directly
4. During nitrogen fixation, they convert
N2 to NH4+, making atmospheric nitrogen
available to other organisms for
incorporation into organic molecules
C. Oxygen relationships:
1. obligate aerobes- require
oxygen to survive
2. facultative anaerobes- can
use it when available, not
required
3. obligate anaerobes – must
avoid oxygen or will die
D. Evolution of metabolism
1. Early prokaryotes were probably
heterotrophs feeding on the “primordial
soup” of early Earth.
2. Glycolysis was probably the first
metabolic process for gaining fuel from
organic materials with no oxygen
3. Eventually, the food supply would be
gone and the prokaryotes that were able
to adapt to drive the synthesis of
organic compounds would survive
4. Early prokaryotes split H2S to obtain
electrons, before using water
VI. The Importance of
Prokaryotes
A. Ecological cycles
1. Decomposers- unlock organics from
corpses and waste products
B. Symbiotic relationships –
organisms in close contact with
each other (symbiont and host)
1. Mutualism (+, +) - Nitrogen fixers
and root nodules
2. Parasitism (+, -) - pathogenic strains
3. Commensalism (+, 0) – host not
affected
C. Pathogenic prokaryotes cause
about half of all human disease,
including pneumonia caused by
Haemophilus influenzae bacteria.
1. Opportunistic: normal residents of host; only
cause illness when defenses are weakened
D. Louis Pasteur,
Joseph Lister,
and
other
scientists
began
linking disease
to pathogenic
microbes in the late 1800s
E. Most pathogens cause illness by
producing poisons, called exotoxins
and endotoxins.
1. exotoxins: proteins that can produce
disease w/o the prokaryote present
a. Clostridium botulinum, which grows
anaerobically in improperly canned foods,
produces an exotoxin that causes botulism.
b. An exotoxin produced by Vibrio cholerae
causes cholera, a serious disease
characterized by severe diarrhea.
c. Even strains of E. coli can be a source of
exotoxins, causing traveler’s diarrhea.
2. Endotoxins: They are originally from the
lipid portion of outer membrane from
gram negative bacteria. They are released
in small amounts when the bacteria divide
and in larger amounts when they die and
disintegrate. They are called endotoxins
because they are not secreted but are part
of the cell itself.
a. The endotoxin-producing bacteria in the genus
Salmonella are not normally present in healthy
animals.
b. Salmonella typhi causes typhoid fever.
c. Other Salmonella species, including some that
are common in poultry, cause food poisoning.
VIII. Prokaryotes in Research
A. Much of what we know about
metabolism and molecular biology
has been learned using prokaryotes,
especially E. coli, as simple model
systems.
B. With increasing use, prokaryotes are
used to solve environmental
problems.
1. organisms to remove pollutants from
air, water, and soil is bioremediation
C. Soil bacteria, called pseudomonads,
have been developed to decompose
petroleum products at the site of oil
spills or to decompose pesticides.
D. The chemical industry produces
acetone, butanol, and other products
from bacteria.
E. The pharmaceutical industry cultures
bacteria to produce vitamins and
antibiotics.
F. The food industry used bacteria to
convert milk to yogurt and various
kinds of cheese.