Transcript Prokaryotes and the Origins of Metabolic Diversity Chapter 27 Part two

Prokaryotes and the Origins
of Metabolic Diversity
Chapter 27 Part two
By: Jonathan, Javeria &
Megan
Nutritional & Metabolic
Activity
Categories of Prokaryotes
 Based on how organism obtains energy and carbon
 Types: Phototrophs, Cehmoautotrophs, Photoheterotrophs, Chemoheterotrophs
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Four main groups of
prokaryotes
Photoautotrophs
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Harness light energy to drive synthesis of organic
compound from carbon dioxide
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Have internal membranes with light-harvestng pigment
systems
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Include cyanobacteria and all photosynthetic eukaryotes
Chemoautotrophs
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Also need CO2 as carbon source, obtains energy by
oxidizing inorganic substances
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Extracts energy from H2S, NH3, Fe(2+)
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Prokayotic groups cont.
Photoheterotrophs
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Uses light to generate ATP
Obtains carbon in organic form
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Chemoheterotrophs
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Consumes organic molecules for both
energy and carbon
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Found in prokaryotes, protests, fungi,
animals, some parasite plants
Nutritional Diversity
Among
Chemoheterotrophs
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Saprobes are decomposers that absorb
nutrients from dead organic matter
Specific nutrients needed for growth extremely
diverse: Latobacillus requires specific medium,
E. Coli has versatile needs
So diverse that some bacteria can metabolize
petroleum
Synthetic organic compounds that can’t be
broken by any chemoautotroph is
nonbiodegradable
Nitrogen Metabolism
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Prokaryotes perform key steps in nitrogen
cycle
Nitrosomonas converts NH3 to NO2(+); some
others perform nitrogen fixation, which is
conversion of N2 to NH3
Photoautotrophs that fix nitrogen only require
light energy, CO2, N2, water and some
minerals
Metabolic Relationships
to Oxygen
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Obligate aerobes use O2 for cellular
respiration
Facultative anaerobes can use either O2 or
fermentation
Obligate anaerobes are poisoned by O2
Either live by fermentation or anaerobic
respiration, inorganic molecules other than
O2 accept electrons at end of electron
transport chain
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All major metabolic capabilities today evolved
in first billion years of life
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Hypotheses are from molecular systematics,
comparisons between prokaryotes, and geological
evidence
Origins of Metabolism
ｷ ATP as universal source of energy points out that it was used
early on
ｷ Glycolysis and chemiosmotic mechanism of ATP synthesis
common to nearly all organisms
ｷ Traditional hypothesis is that earliest cells were
chemoautotrophs, absorbing organic compounds in
environment
ｷ Natural selection soon favored the cells that could produce
ATP
ｷ Favored hypothesis today is that chemoautotrophs obtained
energy from inorganic molecules, then made their own energy
ｷ FeS and H2S were most likely substances first used to make
free energy
-Later evolution would favor cells that developed electron
transport chains
Metabolism?
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The origin of
photosynthesis
 Light absorbing pigments may have protected cells from
harmful excess light and then become coupled with
membrane proteins to drive ATP synthesis.
 Bacteriorhodopsin, the light-energy capturing pigment
in the membrane of extreme halophiles (a group of
archaea), uses light energy to pump H+ out of the cell to
produce a gradient of hydrogen ions. This gradient
provides the power for production of ATP synthesis.
 Components of electron transport chains that functioned
in anaerobic respiration
 in other prokaryotes also may have been chosen to
provide reducing power.
Early Prokaryotes
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The nutritional modes of modern purple and
green sulfur bacteria are the most similar to early
prokaryotes.
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The colors of these bacteria are due to
bacteriochlorophyll, which functions instead of
chlorophyll a as their main photosynthetic
pigment.
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These bacteria split H2S instead of H2O as a
source of electrons, they produce no O2
Cyanobacteria
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The first cyanobacteria evolved a mechanism that reduced CO2
using water as a source of electrons and hydrogen.
release O2 as a by-product of their photosynthesis
Cyanobacteria evolved between 2.5 and 3.4 billion years ago.
Oxygen released by photosynthesis may have first reacted with
dissolved iron ions to precipitate as iron oxide (supported by
geological evidence of deposits), preventing accumulation of free
O2.
Precipitation of iron oxide would have eventually depleted the
supply of dissolved iron and O2 would have accumulated in the
seas.
As seas became saturated with O2, the gas was released into the
atmosphere.
Phylogeny of
Prokaryotes
 Studies of ribosomal RNA indicate the
presence of signature sequences.
 Signature sequences = Domain-specific
base sequences at comparable locations in
ribosomal
 Cynobacteria bloom
Anabaena
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1. Domain Archaea
• three main groups:
• 1. Methanogens are named for their unique form of energy metabolism.
• They use H2 to reduce CO2 to methane (CH4) and are strict anaerobes.
• live in marshes and swamps- methane that bubbles out at these sites
forms marsh gas
• are used in sewage treatment and contribute to the nutrition of cattle and
other herbivores
• 2. Extreme halophiles live in high salinity (15–20%) places (e.g.,Dead
Sea).
• Some species simply tolerate extreme salinities while others require
such conditions
• This pigment is also responsible for the purple-red color of the colonies.
• 3. Extreme thermophiles live in hot environments. (60 – 80°C)
• may be found oxidizing hot sulfur springs and near deep hydrothermal
vents
• are protkayotes which are most closely related to eukaryotes
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Extreme halophiles. Colorful ‘salt loving’
archaea thrive in these ponds near San
Francisco. Used for commercial salt
production, the ponds contain water that is
five to six times as salty as seawater.
2. Domain Bacteria
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Bacteria comprise a majority of the prokaryotes.
Molecular systematics has helped establish about 12 groups of bacteria
Proteobacteria: most diverse group of bacteri and includes photoautotrophic /
photoheterotrophic purple bacteria, chemautrophic & chemoheterotrophic
bacteria
Gram-Positive Bacteria: chemoheterotrophs- form resistant endospores
Cynobacteria: have plantlike photosynthesis
Spirochetes: helical chemoheterotrophs that move in a corkscrew fashion and
cause syphilis & Lyme disease
Chlamydias: are obligate intracellular animal parasites. (STD)
Ecological Impact of
Prokaryotes
Prokaryotes are indispensable links in the
recycling of chemical elements between
the biological and physical worlds.
As decomposers, they return carbon,
nitrogen, and other elements to the
environment for assimilation into new
living forms.
Many prokaryotes are symbiotic
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Symbiosis: an ecological relationship involving direct contact between organisms of
two different species
-probably played a major role in the evolution of prokaryotes and the origin of
eukaryotes
Organisms are called symbionts
-if one is much larger, it is called the host.
Mutualism: both systems benefit
Commensalism: one symbiont benefits while the other is neither harmed nor helped
Parasitism: the symbiont (a parasite) benefits at the expense of the host
One half of all human diseases are caused by pathogenic prokaryotes.
Mutualism: bacterial headlights. The glowing oval below the eye of the flashlight
fish (Photoblepharon palpebratus) is an organ harboring bioluminescent bacteria. The
fish uses the light to attract prey and to signal potential mates. The bacteria receive
nutrients from the fish.
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 Koch’s postulate : four
criteria for establishing a
pathogen as the cause of a
disease
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find the same pathogen in each diseased
individual
isolate and grow the pathogen in a pure
culture
induce the disease in experimental
animals
isolate the same pathogen from the
experimental animal
Prokaryotes & Disease
 Pathogens more commonly cause disease by
producing toxins
 Exotoxins: proteins are secreted by prokaryotes
and are very potent
 Endotoxins: components of the outer membrane
of certain gram-negative bacteria
 Improved hygiene and sanitation and the
development of antibiotics has made living better
 The evolution of antibiotic-resistant strains of
pathogenic bacteria poses a serous health threat
Humans use prokaryotes
in research and
technology
 The diverse metabolic capabilities of
prokaryotes have been used to digest organic
wastes produce chemical products, make
vitamins and antibiotics, and produced food
products such as yogurt and cheese
 Expanded our understanding of molecular
biology and recombinant DNA techniques.
The end!