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Microbial Metabolism

Metabolism of

ExtremophilesChing-Tsan Huang (黃慶璨)

Office: Agronomy Building, Room 111

Tel: (02) 33664454

E-mail: cthuang@ntu.edu.tw

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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).

Extremophiles

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Extreme Acidophiles

Halophiles Thermophiles

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Diverse Environments

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Extreme Temperatures

ClassificationPsychrophile 0 ~ 20 oC

Mesophile 20 ~ 40 oC

Thermophile 40 ~ 80 oC

Hyperthermophile > 80 oC

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.

Temperature

Enzym

e a

ctivity

Q10

10 oC

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Extreme PressureAtmospheric pressureChange 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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Extreme SalineSalinity

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

Ionizing radiation

rays and x-rayslow 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

g raysx-rays

UV lightvisible light

infraredmicrowavesradio waves

Wavelength

increase

Energy

increase

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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 Wallscan 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 BiologyChromosomes

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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Extreme Halophiles Thermophiles Methanogens

use modified Entner-Doudoroff for

glucose catabolism

do not catabolize

glucose significantly

pyruvateacetyl CoA catalyzed by pyruvate oxidoreductase

functional TCA cycle no TCA cycle

have respiratory chains no respiratory chains

use reverse Embden-

Meyerhoff for

gluconeogenesis

use reverse Embden-

Meyerhoff 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

Metabolism

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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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EuryarchaeotaMethanogens

anaerobic environments rich in organic mater

e.g. animal rumens, anaerobic sludge digesters

Halobacteriaaerobic, respiratory, chemoheterotrophs with complex

nutritional requirements

ThermoplasmsThermoacidophiles, lack cell walls

Extremely thermophilic So-metabolizersoptimum growth temperatures 88 – 100°C

strictly anaerobic; reduce sulfur to sulfide; motile by flagella

Sulfate-reducersextremely thermophilic, irregular coccoid cells

use sulfate, sulfite, or thiosulfite as electron acceptor

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Methanogenesis

From CO2 From methyl compound From acetate

CH4CH4

CH4

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Sulfate reduction

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+4

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