Download Prokaryotes are diverse and widespread Prokaryotes are diverse

Bacteria on the point of a pin
Prokaryotes are diverse and widespread
Prokaryotes are diverse and widespread
ƒ Prokaryotic cells are smaller than eukaryotic cells.
ƒ Prokaryotes live in habitats
– Prokaryotes range from 1–5 µm in diameter.
– too cold,
– Eukaryotes range from 10–100 µm in diameter.
– too hot,
ƒ The collective biomass of prokaryotes is at least 10
times that of all eukaryotes.
– too salty,
– too acidic, and
– too alkaline for eukaryotes to survive.
ƒ Some bacteria are pathogens, causing disease.
But most bacteria on our bodies are benign (良性) or
beneficial.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
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Prokaryotes are diverse and widespread
External features contribute to the success of
prokaryotes
ƒ Several hundred species of bacteria live in and on
our bodies,
ƒ Prokaryotic cells have three common cell shapes.
– decomposing dead skin cells,
– supplying essential vitamins, and
– Cocci (球菌) are spherical prokaryotic cells. They
sometimes occur in chains that are called streptococci.
– Bacilli (桿菌) are rod-shaped prokaryotes. Bacilli may
also be threadlike, or filamentous.
– guarding against pathogenic organisms.
ƒ Prokaryotes in soil decompose dead organisms,
sustaining chemical cycles.
– Spiral prokaryotes are like a corkscrew.
– Short and rigid prokaryotes are called spirilla.
– Longer, more flexible cells are called spirochetes.
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© 2012 Pearson Education, Inc.
Bacilli
Cocci
External features contribute to the success of
prokaryotes
ƒ Nearly all prokaryotes have a cell wall. Cell walls
– provide physical protection and
– prevent the cell from bursting in a hypotonic
environment.
ƒ When stained with Gram stain, cell walls of
bacteria are either
– Gram-positive, with simpler cell walls containing
peptidoglycan (肽聚醣), or
Spirochete
Spirochete
– Gram-negative, with less peptidoglycan, and more
complex and more likely to cause disease.
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External features contribute to the success of
prokaryotes
ƒ The cell wall of many prokaryotes is covered by a
capsule (被膜), a sticky layer of polysaccharides
(多醣) or protein.
ƒ The capsule
– enables prokaryotes to adhere to their substrate or to
other individuals in a colony and
Gram-positive (purple) and gram-negative (pink) bacteria
– shields pathogenic prokaryotes from attacks by a host’s
immune system.
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External features contribute to the success of
prokaryotes
ƒ Some prokaryotes have external structures that
extend beyond the cell wall.
扁桃腺
Tonsil cell
Capsule
– Flagella help prokaryotes move in their environment.
– Hairlike projections called fimbriae (菌毛) enable
prokaryotes to stick to their substrate or each other.
Bacterium
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Populations of prokaryotes can adapt rapidly to
changes in the environment
Flagella
ƒ Prokaryote population growth
– occurs by binary fission,
– can rapidly produce a new generation within hours, and
– can generate a great deal of genetic variation
– by spontaneous mutations,
Fimbriae
– increasing the likelihood that some members of the population
will survive changes in the environment.
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Populations of prokaryotes can adapt rapidly to
changes in the environment
Chromosome
Plasmids
ƒ The genome (基因組) of a prokaryote typically
– has about one-thousandth as much DNA as a
eukaryotic genome and
– is one long, circular chromosome packed into a distinct
region of the cell.
ƒ Many prokaryotes also have additional small,
circular DNA molecules called plasmids (質粒),
which replicate independently of the chromosome.
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Populations of prokaryotes can adapt rapidly to
changes in the environment
ƒ Some prokaryotes form specialized cells called
endospores (芽孢; 内生孢子) that remain dormant
through harsh (嚴峻) conditions.
Endospore
ƒ Endospores can survive extreme heat or cold.
An endospore within an anthrax (炭疽熱) bacterium cell
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Prokaryotes have unparalleled (具優勢的) nutritional
diversity
Prokaryotes have unparalleled nutritional
diversity
ƒ Prokaryotes exhibit much more nutritional diversity
than eukaryotes.
ƒ Two sources of carbon are used by prokaryotes.
ƒ Two sources of energy are used.
– Phototrophs capture energy from sunlight.
– Autotrophs obtain carbon atoms from carbon dioxide.
– Heterotrophs obtain their carbon atoms from the
organic compounds present in other organisms.
– Chemotrophs harness the energy stored in chemicals.
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© 2012 Pearson Education, Inc.
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Prokaryotes have unparalleled nutritional
diversity
ƒ The terms that describe how prokaryotes obtain
energy and carbon are combined to describe their
modes of nutrition.
Nutritional mode
Energy source
Photoautotroph
Sunlight
Chemoautotroph
Inorganic chemicals
– Photoautotrophs obtain energy from sunlight and use
carbon dioxide for carbon.
– Photoheterotrophs obtain energy from sunlight but get
their carbon atoms from organic molecules.
Photoheterotroph
Sunlight
Chemoheterotroph
Organic compounds
Carbon source
CO2
Organic compounds
– Chemoautotrophs harvest energy from inorganic
chemicals and use carbon dioxide for carbon.
– Chemoheterotrophs acquire energy and carbon from
organic molecules.
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Biofilms are complex associations of microbes
ENERGY SOURCE
Chemicals
Chemoautotrophs
CO2
Organic compounds
CARBON SOURCE
Sunlight
Photoautotrophs
ƒ Biofilms
– are complex associations of one or several species of
prokaryotes and
Oscilliatoria
Unidentified “rock-eating” bacteria
Photoheterotrophs
Chemoheterotrophs
– may also include protists and fungi.
ƒ Prokaryotes attach to surfaces and form biofilm
communities that
– are difficult to eradicate (根除) and
Rhodopseudomonas
A Bdellovibrio attacking a
larger cell
– may cause medical and environmental problems.
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Biofilms are complex associations of microbes
Biofilms are complex associations of microbes
ƒ Biofilms are large and complex “cities” of microbes
that
ƒ Biofilms
– communicate by chemical signals,
– coordinate (相互配合) a division of labor and defense
against invaders, and
– Clog (阻塞) and corrode (腐蝕) pipes,
– gum up filters and drains (渠道), and
– Coat the hulls (船殼) of ships.
– use channels to distribute nutrients and collect wastes.
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© 2012 Pearson Education, Inc.
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Prokaryotes help clean up the environment
ƒ Prokaryotes are useful for cleaning up contaminants
in the environment because prokaryotes
– have great nutritional diversity,
– are quickly adaptable, and
– can form biofilms.
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Prokaryotes help clean up the environment
Prokaryotes help clean up the environment
ƒ Bioremediation (生物修復) is the use of
organisms to remove pollutants from
ƒ Prokaryotic decomposers are the mainstays (支柱) of
sewage treatment facilities.
– soil,
– air, or
– water.
– Raw sewage is first passed through a series of screens
(篩屏) and shredders (碎化機).
– Solid matter then settles out from the liquid waste,
forming sludge (污泥).
– Sludge is gradually added to a culture of anaerobic
prokaryotes, including bacteria and archaea.
– The microbes decompose the organic matter into material
that can be placed in a landfill (垃圾填埋場) or used as
fertilizer.
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© 2012 Pearson Education, Inc.
Prokaryotes help clean up the environment
ƒ Liquid wastes are treated separately from the
sludge.
– Liquid wastes are sprayed onto a thick bed of rocks.
– Biofilms of aerobic bacteria and fungi growing on the
rocks remove much of the dissolved organic material.
Rotating
spray arm
– Fluid draining from the rocks is sterilized (消毒) and then
released, usually into a river or ocean.
Rock bed coated
with aerobic
prokaryotes
and fungi
Liquid wastes
Outflow
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Prokaryotes help clean up the environment
ƒ Bioremediation is becoming an important tool for
cleaning up toxic chemicals released into the soil
and water by industrial processes.
ƒ Environmental engineers change the natural
environment to accelerate the activity of naturally
occurring prokaryotes capable of metabolizing
pollutants.
Treatment of an oil spill in Alaska
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Bacteria and archaea are the two main branches
of prokaryotic evolution
ƒ New studies of representative (典型的) genomes of
prokaryotes and eukaryotes strongly support the
three-domain view of life.
聚合酶
– Prokaryotes are now classified into two domains:
內子
肽聚醣
– Bacteria and
組蛋白
– Archaea.
– Archaea have at least as much in common with
eukaryotes as they do with bacteria.
pre-rRNA 在形成成熟 rRNA 之前，會有一剪接過程。pre-rRNA 中間有一段序列會被切
除掉；剩餘的序列會再連接起來，成為成熟 rRNA。其中，被切掉的 RNA 序列稱為
「中介序列」(intervening sequence) 或「內子」(intron)，保留下來的序列稱為「外子
」(exon)。
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Archaea thrive (繁生) in extreme environments—
and in other habitats
ƒ Archaeal inhabitants of extreme environments
have unusual proteins and other molecular
adaptations that enable them to metabolize and
reproduce effectively.
– Extreme halophiles (嗜鹽菌) thrive in very salty places.
– Extreme thermophiles (嗜熱菌) thrive in
– very hot water, such as geysers
(熱泉),
and
– acid pools.
Orange and yellow colonies of heat-loving archaea
growing in a Nevada geyser
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Archaea thrive in extreme environments—and in
other habitats
ƒ Methanogens (甲烷菌)
– live in anaerobic environments,
– give off methane as a waste product from
– the digestive tracts of cattle and deer and
– decomposing materials in landfills.
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Bacteria include a diverse assemblage of
prokaryotes
ƒ The domain Bacteria is currently divided into five
groups, based on comparisons of genetic
sequences.
ƒ 1. Proteobacteria (變形菌)
– are all gram negative,
– share a particular rRNA sequence, and
– represent all four modes of nutrition.
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Bacteria include a diverse assemblage of
prokaryotes
– Thiomargarita namibiensis (納米比亞嗜硫珠菌) is a type
of proteobacteria that
– is a giant among prokaryotes, typically ranging up to
0.1-0.3 mm in diameter,
– uses H2S to generate organic molecules from CO2,
and
– produces sulfur wastes, seen as small greenish
globules.
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Bacteria include a diverse assemblage of
prokaryotes
– Proteobacteria also include Rhizobium (根瘤菌) species
that
– live symbiotically in root nodules (瘤) of legumes (豆
科植物) and
Shoot
Bacteria within
囊 vesicle in an
infected cell
Nodules
Roots
– convert atmospheric nitrogen gas into a form usable
by their legume host.
– Symbiosis is a close association between
organisms of two or more species.
– Rhizobium is an endosymbiont, living within another
species.
Root nodules on a soybean plant
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Bacteria include a diverse assemblage of
prokaryotes
ƒ 2. Gram-positive bacteria
– rival (媲美) proteobacteria in diversity and
– include the actinomycetes (放線菌) common in soil.
– Streptomyces (鏈黴菌屬) is often cultured by
pharmaceutical companies as a source of many
antibiotics.
Streptomyces, the source of many antibiotics
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16.9 Bacteria include a diverse assemblage of
prokaryotes
ƒ 3. Cyanobacteria (藍綠菌)
– Cyanobacteria are the only group of prokaryotes with
plantlike, oxygen-generating photosynthesis.
Photosynthetic
cells
– Some species, such as Anabaena, have specialized
cells that fix nitrogen.
Nitrogen-fixing
cells
Anabaena (魚腥藻屬), a filamentous cyanobacterium
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Bacteria include a diverse assemblage of
prokaryotes
ƒ 4. Chlamydias (披衣菌)
– Chlamydias live inside eukaryotic host cells.
– Chlamydia trachomatis (砂眼披衣菌)
– is a common cause of blindness in developing
countries and
– is the most common sexually transmitted disease in
the United States.
Chlamydia cells (arrows) inside an animal cell
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Bacteria include a diverse assemblage of
prokaryotes
ƒ 5. Spirochetes (螺旋菌) are
– helical bacteria and
– notorious (惡名昭彰) pathogens, causing
– syphilis (梅毒) and
– Lyme disease.
Treponema pallidum, the spirochete
that causes syphilis
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Some bacteria cause disease
ƒ All organisms are almost constantly exposed to
pathogenic bacteria.
ƒ Most bacteria that cause illness do so by producing
a poison.
– Exotoxins are proteins that bacterial cells secrete into
their environment.
– Endotoxins are components of the outer membrane of
gram-negative bacteria.
Staphylococcus aureus (金黄色葡萄球菌 ), an
exotoxin producer
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Koch’s postulates are used to prove that a
bacterium causes a disease
Koch’s postulates are used to prove that a
bacterium causes a disease
ƒ Koch’s postulates (假設) are four essential conditions
used to establish that a certain bacterium is the
cause of a disease. They are
ƒ Koch’s postulates were used to demonstrate that
the bacterium Helicobacter pylori (幽門螺旋桿菌) is
the cause of most peptic ulcers (消化性潰瘍).
1. find the bacterium in every case of the disease,
2. isolate the bacterium from a person who has the disease
and grow it in pure culture,
ƒ The 2005 Nobel Prize in Medicine was awarded to
Barry Marshall and Robin Warren for this discovery.
3. show that the cultured bacterium causes the disease
when transferred to a healthy subject, and Robert Koch (1843-1910)
4. isolate the bacterium from the experimentally infected
subject.
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http://commons.wikimedia.org/wiki/File:Robert_Koch_BeW.jpg
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Bacteria can be used as biological weapons
ƒ Bacteria that cause anthrax (炭疽熱) and the
plague can be used as biological weapons.
– Bacillus anthracis (炭疽桿菌) killed five people in the
United States in 2001.
– Yersinia pestis bacteria (鼠疫桿菌)
– are typically carried by rodents (囓齒動物) and transmitted by
fleas, causing the plague and
– can cause a pneumonic (肺炎) form of plague if inhaled.
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http://en.wikipedia.org/wiki/File:Daschle_letter.jpg
Swellings (buboes, 腹股溝淋巴結炎) characteristic of the bubonic
form of plague
Bacteria can be used as biological weapons
ƒ Clostridium botulinum (肉毒桿菌) produces the
exotoxin botulinum, the deadliest poison on earth.
ƒ Botulinum blocks transmission of nerve signals and
prevents muscle contraction.
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