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Unit 2 Part 4 - Microbes as a Component of Extreme
Environments
Extreme environment:
-

Environmental conditions (e
...
pH, temperature, salinity, relative humidity, and nutrients)
are at one of the extreme limits, i
...

2
...

4
...

6
...

8
...

2
...

4
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High pressure

Air-Water Interface Includes
1
...

3
...

5
...
Pathways that catabolize toxic compounds
b
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DNA repair mechanism
High Temperature
(More than 70 to 100C)
In hydrothermal vents, more than 300C
Archaebacteria are known to survive under such conditions
Growth is limited due to:
- Low organic matter
- Low O2
- Acidic and alkaline pH
Very few species of bacteria survive at 75C or more e
...

- Thermus sp
...
g
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Halobacterium
b
...
0
Thermobacillus sp
...

Archaebacteria: The Heros of Extreme Environments

Under extreme condition, archaebacteria are able to survive
On the basis of 16S rRNA analysis of all these bacteria are related to each other
In these bacteria cell wall is unique, which lacks murein (peptidoglycan) and have unusual
linkages in cell membrane lipids
Three Major Groups of Archaebacteria
1
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Halophiles (Salt-resistant)
3
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Methanobacterium
b
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Methanococcus
Family 3: Methanomicrobiaceae
Examples:
a
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Methanogenium
c
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Methanosarcina
They produce methane by reducing CO2 (Chemolithotrophs)
They are obligate anaerobes

They are unable to use CHO, proteins, and other organic substrates
3-Major Groups of Methanogens
Group 1:
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Methanobacterium
Methanobrevibacter

Group 2:
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Methanococcus
Methanospirillum

Group 3:
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Methanosarcina

At least three different types of cell walls are found among these bacteria
The most complex group is Group 1, which is rigid and composed of “Pseudomurein”
Group 2:
- In these bacteria, the cell wall is flexible and composed of chiefly proteins with traces of
“Glucosamine”
Group 3:
- Have most complex, flexible cell wall composed of two layers:
a
...
An outer, composed of entirely proteins resistant to hydrolysis
Halophiles (Salt-resistant)
Genera:
- Halobacterium
- Halococcus
They are obligate halophiles, grow at least at 15% NaCl
- Concentration with unique metabolic features
Light energy is converted to ATP by “bacteriorhodopsin” -a red pigment in the red membrane
In addition to respiration, there is also light-dependent ATP generation

Found under high salty conditions e
...
dead sea, salty lakes, and salt-preserved foods
Thermoacidophiles
These bacteria grow at high temperatures and low pH
Examples:
a
...
Thermoplasma group
c
...
00 pH
- The bacteria rapidly oxidizes H2S
- The principal substrate is “S”
Thermoplasma Group:
- Facultative anaerobic and use small amount of mono and disaccharides as carbon
source and energy supply
- These bacteria are found in coal mines
- Small organic molecules in coal spoils are utilized by the bacteria
- These bacteria lack cell wall, but membrane contains large amount of liposaccharides
and glycoproteins both of which contain mannose
Thermoproteus Group:
- Metabolic activities of these bacteria depend on element sulfur
- The product is H2S, which is required by the organisms in this group
- All are anaerobic
- Two genera of this group are:
a
...
Desulfurococcus
Structural and Physiological Features of Archaebacteria

1
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Glycerol diethers
b
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Cell Wall
The cell wall of archaebacteria do not contain peptidoglycan (Murein)
Some archaebacteria contain pseudomurein
- Which resemble peptidoglycan of eubacteria but differs in chemical composition
The wall of other bacteria contain proteins subunits

3
...
Purple Membrane of Halobacteria
These bacteria have red membrane, which contain “bacteriorhodopsin” pigment
A protein of chemical structure similar to that of “Rhodopsin” pigment of human eye
When the red pigment is excited by high light it pumps proton to outside of the membrane and
establishes hydrogen concentration which results in ATP synthesis



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