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Chapter 27
Prokaryotes
Bacteria on the
point of a pin
Extreme Thermophiles
The Three Domains of Life
Streptococcus strepto=chain coccus=spherical
Bacilli=rod-shaped
Spirilla=helical includes spirochetes
Largest
known
prokaryote
Another large prokaryote
paramecium
Prokaryotes vary in size
from 0.2µ--750µ
Within the past decade, several uncultured bacteria were consecutively
announced as the largest known prokaryotes: Epulopiscium fishelsoni (3),
Beggiatoa sp. (48), and T. namibiensis (83). Over the years, big bacteria have
been described as "megabacteria" or "gigantobacteria" or given names such as
"Titanospirillum" (20,30). The current holder of the biovolume record, a chainforming, spherical sulfur bacterium, T. namibiensis, was discovered only recently
in the sea floor off the coast of Namibia (83). The cells may reach 750 [micro]m
diameter, clearly visible to the naked eye. They form chains of cells that, due to
their light refracting sulfur globules, shine white on the background of black mud
and thus appear as a string of pearls (Thiomargarita = sulfur pearl).
Also the rod-shaped heterotrophic bacterium, Epulopiscium fishelsoni , found in
fish guts may reach a giant size of 80 [micro]m diameter and 600 [micro]m length
(3, 10). The largest reported Archaea are probably the extremely thermophilic
Staphylothermus marinus, which in culture may occasionally have cell diameters
up to 15 [micro]m (19). The smallest prokaryotes are found among both the
Archaea and the Eubacteria. The disk-shaped cells of the archaea,
Thermodiscus, have diameters down to 0.2 [micro]m and a disk-thickness of 0.10.2 [micro]m (87). Under the collective designation of nanobacteria or
ultramicrobacteria, a range of cell forms with diameters down to 0.2-0.3 [micro]m
have been found in both natural samples and cultures (92). Altogether, the
biovolumes of prokaryotic cells may cover a range of more than 10 orders of
magnitude, from
Evolution of Prokaryotic Metabolism
1. The Origin of Glycolysis– First prokaryotes 3.5 billion
years ago, probably (1)anaerobic chemoheterotrophs.
They absorbed organic compounds and used glycolysis
(fermentation) to produce ATP in an atmosphere without
oxygen. All forms of fermentation produced acidic
compounds.
2. The Origin of Electron Transport Chains and
Chemiosmosis– The (2)first proton pumps were probably
for pH regulation. (3)Later some bacteria used the
oxidation of organic compounds to pump H+’s to save ATP
and developed the first Electron Transport Chains.
(4)Some got so good at transporting H+’s that they could
actually develop a gradient and use the influx to drive the
production of ATP.
3. The Origin of Photosynthesis– (5)The first light absorbing
pigments probably provided protection by absorbing UV light.
But all pigments throw off electrons when light shines on
them so why wouldn’t evolution find a way to use the energy
of those electrons? Bacteriorhodopsin in extreme halophiles
(6)uses light energy to pump H+’s out of the cell and produce
a gradient which is then used to produce ATP (cyclic
photophosphorylation with Photosystem I).
Photoheterotrophs
4. Cyanobacteria, Photoautotrophs, Splitting H2O and
Producing O2– (7)Photosystem II evolved in cyanobacteria
and they split water and released free oxygen. The oxygen
was toxic to many organisms which became extinct. (First
Great Extinction) Photoautotrophs
5. Origin of Cellular Respiration– (8)Some prokaryotes
modified their photosynthetic ETC’s to reduce the level of
toxic O2. The purple non-sulfur bacteria still use their
ETC’s for both photosynthesis and respiration. Eventually
(9)some bacteria used O2 to pull electrons through proton
pumps and aerobic respiration began.
aerobic chemoheterotrophs
Cell Walls
All the proteobacteria and the eubacteria have
peptidoglycan cell walls. Archaebacteria have a
different type of cell wall. Cell walls protect bacteria
from cytolysis in hypotonic solutions but can not protect
them from plasmolysis in hypertonic solutions.
Mycoplasmas without cell walls are susceptible to both.
Penicillin denatures (noncompetitive inhibitor) the
enzyme that bacteria use to form their cell walls and
leaves them susceptible to cytolysis.
Gram-positive diplococcus
Gram-positive staphlococcus and Gram-negative diplobacillus
Bacillus with Pilli-used for conjugation, attachment to
surfaces and snorkels for getting oxygen
Bacterial flagella rotate rather than bend
Bacteria with flagella
Bacteria with flagella
Bacteria with flagella
Infolding of the plasma membrane give these bacteria
respiratory membranes and thylakoid-like membranes
Bacteria growing on agar in a petri dish
Mold cultures
An anthrax endospore
Endospores
ARCHAEA
Extreme halophiles in
seawater evaporation
ponds that are up to
20% salt; colors are
from bacteriorhodopsin
a photosynthetic
pigment very similar to
the pigment in our
retinas
Hot springs with extreme thermophiles
Hydrogen Sulfide Metabolizing Chemoautotrophic Archaea
found in sulfur springs
Eubacteria
The Proteobacteria are a major group (phylum) of
bacteria. They include a wide variety of pathogens, such as
Escherichia, Salmonella(rod-shaped Gram-negative
enterobacteria that causes typhoid fever and the foodborne
illness salmonellosis , Vibrio(motile gram negative curvedrod shaped bacterium with a polar flagellum that causes
cholera in humans.) , Helicobacter(stomach ulcers), and
many other notable genera.[1] Others are free-living, and
include many of the bacteria responsible for nitrogen
fixation. The group is defined primarily in terms of ribosomal
RNA (rRNA) sequences, and is named for the Greek god
Proteus (also the name of a bacterial genus within the
Proteobacteria), who could change his shape, because of
the great diversity of forms found in this group.
All Proteobacteria are Gram-negative, with an outer
membrane mainly composed of lipopolysaccharides. Many
move about using flagella, but some are non-motile or rely
on bacterial gliding. The last include the myxobacteria, a
unique group of bacteria that can aggregate to form
multicellular fruiting bodies. There is also a wide variety in
the types of metabolism. Most members are facultatively or
obligately anaerobic and heterotrophic, but there are
numerous exceptions. A variety of genera, which are not
closely related to each other, convert energy from light
through photosynthesis. These are called purple bacteria,
referring to their mostly reddish pigmentation.
Alpha Proteobacteria
Alpha
Proteobacteria
Rocky Mountain Spotted Fever
Ti plasmid
Symbiosis with Legumes
Alpha Proteobacteria
Fruiting bodies of myxobacteria
Helicobacter pylori causes
stomach ulcers
The Rickettsia are Gram-negative, obligate intracellular bacteria that
infect mammals and arthropods.
R. prowazekii is the agent of epidemic typhus. During World War I,
approximately 3 million deaths resulted from infection by this
bacterium. In World War II, the numbers were similar. This agent is
carried by the human louse; therefore, disease is a consequence of
overcrowding and poor hygiene.
Rocky Mountain spotted fever and Q fever remain relatively common.
Rhizobium
Streptomycetes-soil bacteria that produces an antibiotic
Sulfur bacteria that split H2S in photosynthesis
Cyanobacteria with heterocysts-specialized cells
with the enzymes for nitrogen fixation
Another Cyanobacteria
Another Cyanobacteria
Another Cyanobacteria
Cyanobacteria
Cyanobacteria
Algae Blooms
Spirochete
Spirochete that causes Lyme
disease
Bull's-eye rash of a person
with Lyme disease
Bull's-eye rash of a
person with Lyme disease
Deer tick that carries the spirochetes that cause Lyme disease
Spirochete that causes Syphilis
Mycoplasms that cause Chlamydiae
No cell wall and smallest of eubacteria
Mycoplasmas-covering a human fibroblast cell
Chlamydias living
inside an animal
cell
Mycoplasms that
cause Chlamydiae
Mutualism of a bioluminescent bacteria
in a “headlight fish”
The yellow bacillus is a pathogenic bacteria that causes
respiratory infections on the membranes inside the nose.
The blue bacteria on this slide are commensal living on
the membranes inside the nose but causing no harm.
Opportunistic infection
Koch’s postulates
Gram-positive actinomycetes causes tuberculosis
destroys tissues
Clostridium botulinum releases exotoxins in food it is an
obligate anaerobe
Vibrio cholerae releases an exotoxin that causes severe
diarrhea
Salmonella typhi endotoxins that cause typhoid fever,
another species of Salmonella causes common food
poisoning due to endotoxins explains why it takes 12 -48
hours for symptoms to show up
Bioremediation
bacteria breakdown
sewage
Spraying fertilizer on oil spills for Bioremediation
Smaller bacteria attacking
a larger one
Conjugation
“caught in the
act”