Download Metabolism of Extremophiles

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Microbial Metabolism
Metabolism of
Extremophiles
Ching-Tsan Huang (黃慶璨)
Office: Agronomy Building, Room 111
Tel: (02) 33664454
E-mail: [email protected]
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Extremophiles
Definition
Inhabit some of earth's most
hostile environments of
• temperature (-2ºC to
15ºC and 60ºC to 120ºC)
• salinity (3-5 M NaCl)
• pH (<4 and >9)
• pressure (>400
atmospheres).
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Halophiles
Extreme Acidophiles
Thermophiles
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Diverse Environments
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Classification
Psychrophile 0 ~
Mesophile
20 ~
Thermophile
40
Hyperthermophile >
20 oC
40 oC
~ 80 oC
80 oC
Enzyme activity
Extreme Temperatures
Q10
10 oC
Temperature
Microbial growth at high temperature
Increase proportion of saturated lipids in membranes
Increase enzyme stability under high temperatures
Effect of temperature on microbial activities
Too high  disintegrate the cell membranes
Too low  freeze or gel the cell membranes
In general, the Q10 for enzyme is near 2.
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Extreme Pressure
Atmospheric pressure
Change in atmosphere pressure
Microbial activity
Extremely low AP
Water evaporation
Oxygen limitation
Hydrostatic pressure
Hydrostatic pressure increases 1 atm for every 10 m of depth.
1 ~ 400 atm has no or little effect on microbial activity.
Barotolerant and Barophilic
Osmotic pressure
Hypertonic habitats
water move into microbial cells  expand and rupture cells
Hypotonic habitats
water move out microbial cells  dehydrate and shrivel cells
Osmotolerant and Osmophilic
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Salinity
Extreme Saline
Affect osmotic pressure
Denature proteins by disrupt the tertiary structure
Dehydrate cells
Halotolerant and halophilic
Achieve osmotic pressure balance with high intracellular
concentration of glycerol or potassium chloride.
Water activity
The amount of water actually available for microbial use
Depends on the number of moles of water and solute, as
well as the activity coefficients for water the particular solute.
Water Holding Capacity (WHC)
Aerobic soil microorganisms: 50 ~ 70% WHC c.a. 0.98 ~
0.99 aw
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Radiation
g rays
x-rays
UV light
Energy
Wavelength
visible light
increase
increase
infrared
Ionizing radiation
microwaves
rays and x-rays
radio waves
low levels of irradiation  mutation
high dose  destroy nucleic acids and enzymes  cell
death
Ultraviolet radiation
260 nm: the most germicidal wavelength
the adsorption maximum of DNA
UV-induce dimerization
Visible light radiation
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Characteristics of Archaea
 Cell walls: lack peptidoglycan (like eukaryotes).
 Fatty acids: the archaea have ether bonds connecting
fatty acids to molecules of glycerol.
 Complexity of RNA polymerase: both archaea and
eukaryotes have multiple RNA polymerases that contain
multiple polypeptides.
 Protein synthesis: various features of protein
synthesis in the archaea are similar to those of
eukaryotes but not of bacteria.
 Metabolism: various types of metabolism exist in both
archaea and bacteria that do not exist in eukaryotes
Methanogenesis occurs only in the domain Archaea.
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Archaeal Cell Walls
can stain gram positive or gram negative
Stains positive – often thick
homogeneous layer
Stains negative – often surface
layer of protein or glycoprotein
lack muramic acid
lack D-amino acids
resistant to lysozyme and b-lactam antibiotics
some contain pseudomurein
peptidoglycan-like polymer
others contain other polysaccharides, proteins or
glycoproteins
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Archaeal Lipids and Membranes
Bacteria/Eucaryotes
• fatty acids attached to
glycerol by ester
linkages
Archaea
• branched chain
hydrocarbons attached
to glycerol by ether
linkages
• some have diglycerol
tetraethers
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Genetics and Molecular Biology
Chromosomes
one chromosome per cell
closed circular double-stranded DNA
generally smaller than bacterial chromosomes
Have few plasmids
mRNAs
may be polygenic, no evidence of splicing
tRNAs
contain modified bases not found in bacterial or
eukaryotic tRNAs
Ribosomes
70S, shapes differ from bacteria and eukaryotes
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Metabolism
Extreme Halophiles Thermophiles
use modified Entner-Doudoroff for
glucose catabolism
Methanogens
do not catabolize
glucose significantly
pyruvateacetyl CoA catalyzed by pyruvate oxidoreductase
functional TCA cycle
have respiratory chains
use reverse EmbdenMeyerhoff for
gluconeogenesis
no TCA cycle
no respiratory chains
use reverse EmbdenMeyerhoff for
gluconeogenesis
biosynthetic pathways similar to those of other organisms
some fix nitrogen
some use glycogen as
major reserve material
some use glycogen as
major reserve material
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ED: Entner-Doudoroff
EM: Embden-Meyerhof
Glucose degradation via the EMP pathway known for most Bacteria and Eukarya (classical) and
the modified EMP versions reported for Archaea.
Bräsen C et al. Microbiol. Mol. Biol. Rev. 2014;78:89-175
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Taxonomy
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Crenarchaeota
Most are extremely thermophilic
Many are acidophiles
Many are sulfur-dependent
for some, used as electron acceptor in anaerobic
respiration
for some, used as electron source
(chemolithotrophs)
Almost all are strict anaerobes
Grow in geothermally heated water or soils that
contain elemental sulfur
Include organotrophs and lithotrophs (sulfur-oxidizing
and hydrogen-oxidizing)
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Methanogens
Euryarchaeota
anaerobic environments rich in organic mater
e.g. animal rumens, anaerobic sludge digesters
Halobacteria
aerobic, respiratory, chemoheterotrophs with complex
nutritional requirements
Thermoplasms
Thermoacidophiles, lack cell walls
Extremely thermophilic So-metabolizers
optimum growth temperatures 88 – 100°C
strictly anaerobic; reduce sulfur to sulfide; motile by flagella
Sulfate-reducers
extremely thermophilic, irregular coccoid cells
use sulfate, sulfite, or thiosulfite as electron acceptor
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Methanogenesis
From CO2
From methyl compound From acetate
CH4
CH4
CH4
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Sulfate reduction
+6
+4
-2