Prokaryotes are diverse and widespread. Prokaryotes are diverse and widespread. Prokaryotes live in habitats

Bacteria on the point of a pin Prokaryotes are diverse and widespread Prokaryotes are diverse and widespread ƒ Prokaryotic cells are smaller than e...
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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.

© 2012 Pearson Education, Inc.

© 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. © 2012 Pearson Education, Inc.

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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.

© 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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.

© 2012 Pearson Education, Inc.

© 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. © 2012 Pearson Education, Inc.

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.

© 2012 Pearson Education, Inc.

© 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.

© 2012 Pearson Education, Inc.

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.

© 2012 Pearson Education, Inc.

© 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 © 2012 Pearson Education, Inc.

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)。

© 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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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.

© 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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. © 2012 Pearson Education, Inc.

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.

© 2012 Pearson Education, Inc.

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