Download Microbial Origins of Life and Energy Conversions

Microbial Origins of Life and
Energy Conversions
Biol 251
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Terms to Know for this Lecture

Science – Questioning

Religion - Believing
Fact – What most experts agree on…
often becomes dogma (essentially the truth)


Truth – What is… does anyone really know
what truth is? Inherent bias…
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The “Big Bang” and Earth

The universe was created sometime
about 13.5 billion years ago from a
cosmic explosion that hurled matter
and in all directions (the “big bang”)
 The
Earth is thought to have
formed about 4.5-4.6 billion
years ago
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Geologic Time….
Oldest sedimentary rocks, Greenland  3.8 bya
CH4 dominated
environment
O2 accumulates
rapidly
[CH4] [CO2] [H2O]
Atmosphere is warm 2.3 bya photosynthetic
 3.5 bya anaerobic cyanobacteria
prokaryotes
lithotrophic and or Atmosphere is cold
fermentative
Western Australia
South Africa
1.7 bya
2.4 bya origin of
eukaryotic cells
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Origin of Early Life  3.8 bya
The primitive Earth was hot
(>100°C), anaerobic with warm
oceans
Simple organic molecules formed
from atmospheric gases (CO2,
NH3, H2S, CH4, HCN and CO) and
dissolved in the oceans
Lightning, heat & UV light - energy
Simple macromolecules:
sugars, amino acids, nucleotides,
lipids
How do simple organic molecules form a protocell?
Spontaneous generation?
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Experimental Results
Laboratory experiments that
attempt to address how cells
developed
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Primordial Soup Experiment 1953
Replicate environmental conditions of
prebiotic times
 Atmosphere


H2O, H2, CH4 & NH3
Organic compounds
 Amino acids

This experiment has been modified
over the last 50 years and has yielded
all 20 amino acids, nucleotides, lipids,
sugars and ATP
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Protocells
All cells have a outer plasma membrane
 Protocells

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
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3.8 bya
Simple membrane bound sacs
Created simple membranes under laboratory
conditions

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Fatty acids & alcohols
Bubble hypothesis
Proteinoids

“protein-like” molecules that are produced when amino
acid solutions are heated
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What was hereditary material of
early organisms? - RNA
Genetic & enzymatic components of early
cells were probably RNA
 Lab experiments have produced

RNA
 Ribozymes

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Enzymatic RNA molecule that catalyzes reactions
during RNA splicing
Clay can concentrate charged molecules

Catalysis of polymers
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Classification and naming of bacteria by how
they derive energy and carbon
4 parts to name
1. How they get energy (chemo- versus photo-)
2. Where they get electrons from? Organic versus
inorganic molecules (organo- versus litho- (rock eater)
3. Where do they get their carbon from? Auto- (CO2) versus
hetero- (organic carbon source- e.g., glucose)
4. Add troph…
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What were earliest organisms (bacteria?) like
metabolically?
Aerobic versus anaerobic?
Photo- versus chemotrophic?
Litho- versus organotrophic?
Auto- versus heterotrophic?
Optimal growth temperature…
Psychrophile: <15° C
Mesophile: From 20 to 40° C
Moderate Thermophiles: 40 to 80° C
Hyperthermophiles: > 80°C
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Stromatolites
Banded domes of sedimentary
rock similar to layered mats
of heterotrophic bacteria &
cyanobacteria
Stromatolites in western Australia
 3.5 billion years old
microscopic resemblance to
photosynthetic organisms
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The Origin of Prokaryotes

Fossils of microbes dating from 950 mya

Palaeolyngbya from Shale in Siberia
Divisions reminiscent of membranes or cell walls
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When did eukaryotes arise?
Sterols, including cholesterol have
been found in oil droplets within
quartz crystals
 Sterols are produced almost
exclusively by eukaryotes
 Quartz is dated at 2.4 bya
 Predates the “Great Oxidation Event”
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O2 production by cyanobacteria
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The oldest eukaryotic fossils are 2.1 bya
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How did organelles develop?
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Theory of Endosymbiosis

page 125
Symbiotic relationship between two
microorganisms, in which one is living
inside the other

Chloroplast
Cyanobacterium engulfed by larger organism
 Photosynthesis provided carbohydrates &
produced O2
 Protected habitat for the cyanobacterium

Both organisms benefit - mutualism
 Relationship became obligatory

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Evidence for Endosymbiosis

Modern chloroplasts
Circular chromosome with prokaryoticlike genes
 Independent division
 Prokaryotic ribosomes
 Has 16s rRNA gene in genome and 16s
rRNA molecule in ribosome

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Endosymbiosis

Mitochondria
Circular chromosome with prokaryotic like
genes
 Independent division
 Prokaryotic like ribosomes
 Prokaryotic like membranes
 Has 16s rRNA gene in genome and 16s
rRNA molecule in ribosome

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Endosymbiosis

Eukaryotes
Fusion of bacterial & archaeal cells
 Genomes fused
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Eukaryotic flagella & cilia

Consequence of a spiral bacterium & a
eukaryotic cell
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Relationships that support the
Theory of Endosymbiosis

Many protozoans are infected with
bacteria in an Endosymbiotic
relationship

Many symbiotic relationships between
microorganisms in nature

Lichens

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Cyanobacterium or alga with a fungus
Cyanobacteria are endosymbionts of plants,
various protists and sponges
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Bacteria
Archaea
Eukarya
Node - LUCA
Last Universal Common Ancestor
Hyperthermophile
Anaerobe
Archaea or Bacteria?
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Thermotoga maritima
A model for LUCA
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Deep sea thermal vents

Grows at 90ºC so hyperthermophile (Domain
Bacteria)
Anaerobic
 Heterotroph
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Must consume carbon compounds
Contains genes that can be classified as…
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
Bacterial
Archaeal

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¼ of the genes
Eukaryotic
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Deep Sea Hydrothermal Vents
Water temperatures >350°C
Minerals precipitate out of sea water
“Black Smoker” … smoke is
precipitate of metal sulfides from H2S
Tremendous diversity of
marine organisms surrounding
thermal vents
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Global Energy Conversions –
Microbes Rule the Earth!!
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Microbes comprise nearly
half of all biomass on Earth
All habitats that support plants and animals
have abundant populations of microorganims.
Microorganisms also exist in habitats too
extreme for plants and animals.
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Prokaryotes are the most abundant
form of life on Earth
Greatest amount of biomass and total numbers of species
Prokaryotes compose 90 % of the total combined weight
of all organisms in the oceans
> 109 bacterial cells are present in 1.0 g of
agricultural soil
Outnumber all eukaryotic cells by 10,000 : 1
 3,000 species of Bacteria and Archaea
are currently recognized
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The main role of microorganisms in
the biosphere is to act as catalysts
of biogeochemical cycles.
Microorganisms catalyze
reactions that cycle C, N, O, P
and many other elements.
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BIOGEOCHEMICAL CYCLES
• Elements required for cells are constantly
progressing through a cycle involving microorganisms
• Leaf falls from tree
• Decomposes
• Elements making leaf used by microbes
• Four key elements constitute four primary cycles
• CARBON
• NITROGEN
• SULFUR
• PHOSPHORUS
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Carbon Cycle
www.textbookofbacteriology.net
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The Carbon Cycle
• Carbon is fixed when photosynthetic organisms fix
CO2 into organic compounds
• Herbivores consume plants
• Carbon from herbivores recycled by four mechanisms
• Exhaled CO2 is used by photosynthetic organisms
• Feces utilized by soil microbes
• Prey for carnivores
• Dead animals are decomposed by soil microbes
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The Carbon Cycle
• Prehistoric decomposed
matter was converted into
fossil fuels
• Burning of fossil fuels
generates CO2
• CO2 reenters cycle
through photosynthetic
plants
• Methanogens reduce CO2
anaerobically and give off CH4
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Nitrogen Cycle

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N2 gas is the most abundant (~80%) gas in Earth’s
atmosphere
Involves several types of microbes
4 types of reactions
 Nitrogen fixation – ONLY by prokaryotes
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N2 gas is converted to NO2- (nitrite) , NO3- (nitrate) , or
NH3 (ammonium salts)
Ammonification
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Bacteria degrade of organic compounds to ammonia
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Convert NH3 to NO2- and NO3-
Nitrification
Denitrification – ONLY by prokaryotes
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Microbial conversion of various nitrogen salts back to
atmospheric N2
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Nitrogen Cycle
www.textbookofbacteriology.net
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Free Living Nitrogen-Fixing Organisms
•NITROGENASE complex – ONLY in prokaryotes!!!!!
• Enzyme of nitrogen-fixation
• Two protein subunits that work together
• Destroyed by O2
• Nitrogenase must be maintained in an anaerobic environment
• Cyanobacteria - fix nitrogen in specialized cells HETEROCYSTS
• Provide anaerobic environment required for nitrogenase
• Plant-associated bacteria – many produce nodules
• In nodules, plant produces a unique form of hemoglobin called
leghemoglobin
• This protein binds O2 and “protects” nitrogenase
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Symbiotic Nitrogen Fixing Organisms
• Rhizobium species - infect roots of legumes (Pea Family of Plants)
• Alfalfa, peas, beans, clover, soybeans, & peanuts
• Attach to root hair, “infection thread” forms
• Bacteria enter through thread and penetrate root cells
• Bacteria differentiate into BACTEROIDS
•Thicker cell walls
•Combination of plant & bacterial cell wall
• Dense cytoplasm
• Do not divide
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Consume carbohydrates from the plant
and fix N2
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Synthesize amino acids
Causes enlargement of root cells
Results in formation of a root NODULE
Bacteria within nodule fix nitrogen
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Plant use amino acids
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Nodules
Rhizobium & Bradyrhizobium
Symbiotic association with legume roots
Alfalfa
N2 + 8H+ + 8e- + 16 ATP  2NH3 + H2 + 16 ADP + 16 Pi
Beans
Clover
Peas
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Deamination
• After N2 is fixed
• Converted to biologically relevant molecules
• Majority of atmospheric nitrogen is incorporated into amino
acids
• Plant is consumed and amino acids incorporated into herbivore
• Herbivore excretes waste
• Microbes break down proteins into amino acids
• A second set of microbes break amino acids down into ammonia
• DEAMINATION
• Often times NH3 is released into soil
• AMMONIFICATION
• Highly soluble in moist soil
• Available to plants and other microbes
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Nitrification – ONLY in
prokaryotes
• Not all NH3 is used by plants
• Some moves to next step in cycle
• Some organisms oxidize NH3 to produce nitrite (NO2-)
• NITRIFICATION
• Nitrosomonas
• Nitrite is further oxidized to nitrate (NO3-)
• Easily moves through soil via diffusion
• Nitrobacter
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Denitrification – ONLY in
prokaryotes
• NO3- (nitrate) can be used as terminal electron acceptor
• under anaerobic conditions
• Results in conversion of NO3- to atmospheric nitrogen N2
• Three reactions involved in process
• Completes nitrogen cycle
NO NO 3
2
N2O
N2
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