CHAPTER 27 Prokaryotes and the Origins of Metabolic Diversity

CHAPTER 27 Prokaryotes and the Origins of

Metabolic Diversity

o Prokaryotes - earliest organisms on Earth and evolved alone for 1.5 billion years..o Their collective biomass outweighs all

eukaryotes combined by at least tenfold.o 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.

They’re (almost) everywhere! They’re (almost) everywhere!

Prokaryotes are wherever there is life and they thrive in habitats that are too cold, too hot, too salty, too acidic, or too alkaline for any eukaryote

Archaea - has extremophiles - ‘like’ extremes!

Fig. 27.1

Live in Extreme places -

Obsidian’s pool

Thermophile - remember these from PCR!!

o Some harmful - Diseases caused by bacteria include tuberculosis, cholera, STDs

o Bacteria in our intestines produce important vitamins.

o Prokaryotes recycle carbon, nitrogen between organic matter and the soil and atmosphere.

o Prokaryotes and eukaryotes in symbiotic relationships (cellulose digestion and cows!).

o Mitochondria and chloroplasts evolved from prokaryotes that became residents in larger host cells (endosymbiosis)

Biological significance-

o Structure and metabolism varies.o 400,000 to 4 million species.

Diversity of prokaryotes

o The archaea inhabit extreme environments and differ from bacteria in many key structural, biochemical, and physiological characteristics.

Bacteria and archaea are the two main branches of prokaryote evolution

Bacteria and archaea are the two main branches of prokaryote evolution

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o Most prokaryotes - unicellular; diameters in the range of 1-5 um, compared to 10-100 um for most eukaryotic cells

o Some species aggregate forming colonies, (division of labor)

o The most common shapes among prokaryotes are spheres (cocci), rods (bacilli), and helices.

Fig. 27.3

Size and shape of prokaryotesSize and shape of prokaryotes

o Prevents the cell from bursting in a hypotonic environment.

o Most bacterial cell walls contain peptidoglycan, a polymer of modified sugars cross-linked by short polypeptides.

o Archaea lack peptidoglycan.

Prokaryotes have a cell wall outside plasma membrane

Prokaryotes have a cell wall outside plasma membrane

Gram stainingGram staining

Positive or negative

o Gram-positive bacteria - simpler cell walls, with large amounts of peptidoglycans. (not harmful usually)

o Gram-negative bacteria have more complex cell walls and less peptidoglycan. (very harmful). An outer membrane on the cell wall contains lipopolysaccharides, carbohydrates bonded to lipids. Lipolysaccharide is antibiotic resistant and is not easily attacked by host - escape detection

Gram stain identifies differences in cell walls of bacteria

Gram stain identifies differences in cell walls of bacteria

Many antibiotics, including penicillin, inhibit the synthesis of cross-links in peptidoglycans, preventing the formation of a functional wall, particularly in gram-positive species. Bacteria bursts from water entry!

Antibiotics like penicillin prevent cell wall formation

Antibiotics like penicillin prevent cell wall formation

Capsule, outside the cell wall (smooth bacteria of Griffith); protection

Capsules adhere the cells to their substratum. They may increase resistance to host defenses. They glue together the cells of those prokaryotes

that live as colonies.

Capsule - outside cell wallCapsule - outside cell wall

Sex pili

Prokaryotic - solid core of protein, no membrane, spinning ‘propeller’

Eukaryotic - microtubules, covered by plasma membrane, oar like with a power stroke

Prokaryotic and Eukaryotic flagellaProkaryotic and Eukaryotic flagella

A second motility mechanism is found in spirochetes, helical bacteria. Two or more helical filaments under the cell

wall are attached to a basal motor attached to the cell.

When the filaments rotate, the cell moves like a corkscrew.

A third mechanism occurs in cells that secrete a jet of slimy threads that anchors the cells to the substratum. The cell glides along at the growing end of

threads.

o No nucleus, only nucleoid without nuclear membrane.o Circular main chromosome - fewer genes than

eukaryotes, less histoneso Plasmid DNA - antibiotic resistance genes, replicate

independently

3. 3. Prokaryotic genome and structure- Prokaryotic genome and structure-

o No membrane bound organelles - so how do cyanobacteria photosynthesize and how do aerobic bacteria undergo cell respiration?

o Plasma membrane has the required enzymes for both processes

o Protein synthesis - overall the same but many factors/proteins involved are different

o Prokaryotes reproduce asexually by binary fission (no genetic variation)

o Transformation, transduction, conjugation, transposition, and mutation cause variation/recombination

o Growth -’multiplication’ - doubles every 20 min.o Geometric growth indicates this rapid rise

Prokaryotes grow and adapt rapidlyProkaryotes grow and adapt rapidly

Fig. 27.9

Unfavorable conditions - form endospores. In an endospore, a cell replicates its

chromosome and surrounds one chromosome with a durable wall.

While the outercell may disinte-grate, an endospore,such as this anthraxendospore, dehy-drates, does notmetabolize, andstays protectedby a thick, protective wall.

Fig. 27.10

Prokaryotes form endosporesProkaryotes form endospores

Sterilization under high pressure and high heat kills endospores

Endospores can remain dormant for centuries!

Prokaryotes compete with other prokaryotes for space and nutrients. Many microorganisms release antibiotics,

chemicals that inhibit the growth of other microorganisms (including certain prokaryotes, protists, and fungi).

Humans use some of these compounds to combat pathogenic bacteria.

Antibiotic resistance is a growing problem!

Prokaryotes can be killed by antibiotics - drugs released by other microorganisms

Prokaryotes can be killed by antibiotics - drugs released by other microorganisms

Prokaryotes - nutritionProkaryotes - nutritiono Phototrophs - use light energy

oChemotrophs - use chemical energy (H2S, NH3, Fe2+)

oAutotrophs - only need CO2 as carbon source (for photosynthesis or chemosynthesis)

oHeterotrophs - need at least one organic source of carbon

-Photoautrophs (cyanobacteria)

-Chemoautrophs

-Photoheterotroph

- Chemoheterotrophs

Saprobes, decomposers that absorb nutrients from dead organisms, and Parasites, which absorb nutrients from the body fluids of living hosts

Examples - look here

Nitrogen - in the form of gas - not accesible to living things except PROKARYOTES! Some chemoautotrophic bacteria convert

ammonium (NH4+) to nitrite (NO2

-).

Others “denitrify” nitrite or nitrate (NO3-) to N2,

returning N2 gas to the atmosphere.

A diverse group of prokaryotes, including cyanobacteria, can use atmospheric N2 directly.

During nitrogen fixation, they convert N2 to NH4+,

making atmospheric nitrogen available to other organisms for incorporation into organic molecules.

Prokaryotes - nitrogen fixation (review)Prokaryotes - nitrogen fixation (review)

Nitrogen cycleNitrogen cycle

. Nitrogen fixing cyanobacteria are the most self-sufficient of all organisms. They require only light energy, CO2, N2, water

and some minerals to grow

Fig. 27.11

o Obligate aerobes - require O2 for cellular respiration.

o Facultative anerobes - will use O2 if present but can also grow by fermentation in an anaerobic environment.

o Obligate anaerobes - poisoned by O2 and use either fermentation or anaerobic respiration.

Oxygen use in prokaryotesOxygen use in prokaryotes

The very first prokaryotes were heterotrophs (important). Where did they get NRG and Carbon?

From the pool of organic molecules in the “primordial soup” of early Earth.

Photosynthesis in prokaryotesPhotosynthesis in prokaryotes

Evolution of photosynth. & cell resp.Evolution of photosynth. & cell resp.

1) Heterotroph

Absorbs glucose from primordial soup

Anaerobic fermentation Glucose

might run out

2) Chemoautotroph

Can make ATP using H2S/ chemicals

Nonoxygenic photosynthesis

Anaerobic fermentation

3)Photoautotroph

Anaerobic fermentation

Evolution of photosynth. & cell resp.Evolution of photosynth. & cell resp.

Makes glucose using photosynthesis Oxygenic

photosynthesis

2) Chemoautotroph

Can make ATP using H2S/ chemicals

Nonoxygenic photosynthesis

Anaerobic fermentation

3)Photoautotroph

Anaerobic fermentation

Aerobic respiration

4) Photoautotroph (cyanobacteria)

First prokaryotes - only glycolysis (anerobic fermentation - heterotrophs)

Limited supply of glucose/carbon source Natural selection of photosynthetic organism Cyanobacteria ancestor used nonoxygenic

photosynthesis (single photosystem using H2S?)

Cyanobacteria - 3.5 billion years old - oxygenic photosynthesis using double photosystem - PSII and PSI; O2 accumulation - 2.7 billion years ago

Aerobic Cell respiration used O2 to extract energy from photosynthesis end products.

Photosynthetic groups are scattered among diverse branches of prokaryote phylogeny.

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Fig. 27.12

Woese used signature sequences, regions of SSU-rRNA that are unique, to establish a phylogeny of prokarotes.

Fig. 27.13

- “lovers” of extreme environments. Archaea can be classified into methanogens

(anaerobes, sewage treatment, guts of herbivores, greenhouse gas), extreme halophiles (high salt -Dead sea, red due to a pigment) and extreme thermophilies (deep sea volacanic vent, hot springs)

Archaea - extremophiles….Archaea - extremophiles….

Prokaryotes- ‘bacteria’ diversityProkaryotes- ‘bacteria’ diversity

Recycling - decomposers (organic to inorganic); and return organic compounds back to inorganic form Ex: Fix nitrogen - cyanobacteria! And release nitrogen back

Symbiosis - several types - mutualism (gut bacteria/termites, root nodules of legumes for nitrogen fixation), parasitism, commensalism

1. 1. Prokaryotes- significanceProkaryotes- significance

Some pathogens are opportunistic. These are normal residents of the host, but

only cause illness when the host’s defenses are weakened.

Louis Pasteur, Joseph Lister, and other scientists began linking disease to pathogenic microbes in the late 1800s.

Robert Koch was the first to connect certain diseases to specific bacteria. He identified the bacteria responsible for

anthrax and the bacteria that cause tuberculosis.

Read on your own from here…..Read on your own from here…..

Koch’s methods established four criteria, Koch’s postulates, that still guide medical microbiology.(1) The researcher must find the same

pathogen in each diseased individual investigated,

(2) Isolate the pathogen form the diseased subject and grow the microbe in pure culture,

(3) Induce the disease in experimental animals by transferring the pathogen from culture, and

(4) Isolate the same pathogen from experimental animals after the disease develops.

These postulates work for most pathogens, but exceptions do occur.

Some pathogens produce symptoms of disease by invading the tissues of the host. The actinomycete that causes tuberculosis is

an example of this source of symptoms. More commonly, pathogens cause illness

by producing poisons, called exotoxins and endotoxins.

Exotoxins are proteins secreted by prokaryotes.

Exotoxins can produce disease symptoms even if the prokaryote is not present. Clostridium botulinum, which grows

anaerobically in improperly canned foods, produces an exotoxin that causes botulism.

An exotoxin produced by Vibrio cholerae causes cholera, a serious disease characterized by severe diarrhea.

Even strains of E. coli can be a source of exotoxins, causing traveler’s diarrhea.

Endotoxins are components of the outer membranes of some gram-negative bacteria. The endotoxin-producing bacteria in the

genus Salmonella are not normally present in healthy animals.

Salmonella typhi causes typhoid fever. Other Salmonella species, including some

that are common in poultry, cause food poisoning.

Since the discovery that “germs” cause disease, improved sanitation and improved treatments have reduced mortality and extended life expectancy in developed countries. More than half of our antibiotics (such as

streptomycin and tetracycline) come from the soil bacteria Streptomyces.

The decline (but not removal) of bacteria as threats to health may be due more to public-health policies and education than to “wonder-drugs.”

For example, Lyme disease, caused by a spirochete spread by ticks that live on deer, field mice, and occasionally humans, can be cured if antibiotics are administered within a month after exposure.

If untreated, Lyme disease causes arthritis, heart disease, and nervous disorders.

The best defense is avoiding tick bites and seeking treatment if bitten and a character-istic rash develops.

Fig. 27.17

Today, the rapid evolution of antibiotic-resistant strains of pathogenic bacteria is a serious health threat aggravated by imprudent and excessive antibiotic use.

Although declared illegal by the United Nations, the selective culturing and stockpiling of deadly bacterial disease agents for use as biological weapons remains a threat to world peace.

Humans have learned to exploit the diverse metabolic capabilities of prokaryotes for scientific research and for practical purposes. Much of what we know about metabolism and

molecular biology has been learned using prokaryotes, especially E. coli, as simple model systems.

Increasing, prokaryotes are used to solve environmental problems.

The application of organisms to remove pollutants from air, water, and soil is bioremediation. The most familiar example is the use of prokaryote

decomposers to treat human sewage. Anaerobic bacteria

decompose theorganic matterinto sludge(solid matterin sewage), whileaerobic microbesdo the same toliquid wastes.

Fig. 27.18

Soil bacteria, called pseudomonads, have been developed to decompose petroleum products at the site of oil spills or to decompose pesticides.

Fig. 27.19

Humans also use bacteria as metabolic “factories” for commercial products. The chemical industry produces acetone,

butanol, and other products from bacteria. The pharmaceutical industry cultures bacteria

to produce vitamins and antibiotics. The food industry uses bacteria to convert

milk to yogurt and various kinds of cheese. The development of DNA technology has

allowed genetic engineers to modify prokaryotes to achieve specific research and commercial outcomes.