The Extreme and Capabilities of Microbial Growth
ENV 411
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1
Chapter 2
The Extreme And
Capabilities of Microbial Growth
Chapter Overview
THE EXTREMES AND CAPABILITIES
OF MICROBIAL GROWTH.
Extremophiles
Different types of extremophiles
Adaptation of acidophile and alkaliphile
Extremophiles in nature and
biotechnology
1 |t h e e x t r e m e & c a p a b i l i t i e s o f m i c r o b i a l g r o w t h
Chapter 2
The Extreme and Capabilities of Microbial Growth
ENV 411
LEARNING OBJECTIVES:
After studying this chapter, you should be able to:
1.
Define extremophiles
2.
Differentiate the different types of extremophiles
3.
Explain adaptations of acidophiles and alkaliphiles
4.
Discuss the value of extremophiles in nature and biotechnology
1.
2.1
2. ARE EXTREMOPHILES?
WHAT
3.
An extremophile is an organism that thrives in and may even require physically or
4.
geochemically extreme conditions that are detrimental to the majority of life on Earth. Most
extremophiles are microbes. The domain Archaea contains renowned examples, but
extremophiles are present in numerous and diverse genetic lineages of both bacteria and
archaeans.
Types of extremophiles
There are many different classes of extremophiles, each corresponding to the way its
environmental niche differs from mesophilic conditions. These classifications are not
exclusive. Many extremophiles fall under multiple categories. For example, organisms living
inside hot rocks deep under Earth's surface are both thermophilic and barophilic.

Acidophile: An organism with an optimum pH level at or below pH 3.

Alkaliphile: An organism with optimal growth at pH levels of 9 or above.

Barophile: Bacteria which live in environments characterized by high gas or liquid
pressure; synonymous with piezophile.
Extremophiles and astrobiology
Astrobiology is the field concerned with forming theories about the distribution, nature, and
future of life in the universe. In it, microbial ecologists, astronomers, planetary scientists,
geochemists, philosophers, and explorers cooperate to constructively guide the search for
life on other planets. Astrobiologists are particularly interested in studying extremophiles, as
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The Extreme and Capabilities of Microbial Growth
ENV 411
Chapter 2
many organisms of this type are capable of surviving in environments similar to those known
to exist on other planets. For example, Mars may have regions in its deep subsurface
permafrost that could harbor endolith communities. The subsurface water ocean of Jupiter's
moon Europa may harbor life, especially at hypothesized hydrothermal vents at the ocean
floor.
2.2
ACIDOPHILE, ALKALIPHILE, BAROPHILE AND CAPNOPHILE
Acidophiles
Acidophilic organisms are those that thrive under highly acidic conditions (usually at pH
2.0 or below) . These organisms can be found in different branches of the tree of life,
including Archaea, Bacteria, and Fungus. Examples of bacteria include:

Acidobacterium[3]a phylum of the Bacteria

Acidithiobacillales, an order of Proteobacteria

Thiobacillus ferrooxidans, T. thiooxidans, T. prosperus, T. acidophilus, T. organovorus,
T. cuprinus

Acetobacter aceti, a bacterium that produces acetic acid (vinegar) from the oxidation of
ethanol.
Alkaliphiles
Alkaliphiles organisms are microbes are those that thrive in alkaline environments with a pH
of 9 to 11 such as soda lakes and carbonate-rich soils.
Barophile
Barophiles are bacteria which live in high pressure environments. They are generally found
on ocean floors, where pressure generally exceeds 380 atm (38 MPa). Some have been
found at the bottom of the Pacific Ocean where the maximum pressure is roughly 117 MPa.
Obligate barophiles cannot survive outside of such environments. For example, the
Halomonas species Halomonas salaria requires a pressure of 1000 atm (100 MPa) and a
temperature of 3 degrees Celsius. Barotolerant bacteria are able to survive at high
pressures, but can exist in less extreme environments as well.
Barophiles grow in darkness, and so are very uv sensitive, they lack many mechanisms of
DNA repair.
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Chapter 2
The Extreme and Capabilities of Microbial Growth
ENV 411
Capnophile
.
Capnophiles are microorganisms which thrive in the presence of high concentrations of
carbon dioxide, or which require the presence of carbon dioxide to survive. Capnophiles are
found in environments such as the stomachs of ruminant animals. One example,
Mannheimia succiniciproducens, is known to fix carbon dioxide and produce succinic acid.
An example of a capnophile is the Gram-negative Aggregatibacter spp. found in the mouth.
Aggregatibacter actinomycetemcomitans is one of the causes of aggressive juvenile
periodontitis.
2.3
MECHANISM OF ADAPTATION OF ACIDOPHILE AND ALKALIPHILE
Most acidophilic organism have evolved extremely efficient mechanisms to pump
protons out of the intracellular space in order to keep the cytoplasm at or near neutral pH.
Therefore, intracellular proteins do not need to develop acid stability through evolution.
However, other acidophiles, such as Acetobacter aceti, have an acidified cytoplasm which
forces nearly all proteins in the genome to evolve acid stability. For this reason, Acetobacter
aceti has become a valuable resource for understanding the mechanisms by which proteins
can attain acid stability.
Studies of proteins adapted to low pH have revealed a few general mechanisms by which
proteins can achieve acid stability. In most acid stable proteins (such as pepsin and the soxF
protein from Sulfolobus acidocaldarius), there is an overabundance of acidic residues which
minimizes low pH destabilization induced by a buildup of positive charge. Other mechanisms
include minimization of solvent accessibility of acidic residues or binding of metal cofactors.
In a specialized case of acid stability, the NAPase protein from Nocardiopsis alba was
shown to have relocated acid-sensitive salt bridges to regions that play an important role in
the unfolding process. In this case of kinetic acid stability, protein longevity is accomplished
across a wide range of pH.
Alkaliphile
To survive, alkaliphiles maintain a relatively low alkaline level of about 8 pH inside their cells
by constantly pumping hydrogen ions (H+)in the form of hydronium ions (H3O+) across their
cell membranes into their cytoplasm.
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The Extreme and Capabilities of Microbial Growth
ENV 411
Chapter 2
Examples include: (i) Geoalkalibacter ferrihydriticus, (ii) Bacillus okhensis,(iii) Alkalibacterium
iburiense
At this point you should be able to:

Define extremophiles

Differentiate the different types of extremophiles

Explain adaptations of acidophiles and alkaliphiles

Discuss the value of extremophiles in nature and biotechnology
1. Student are required to retrieve the information of the following extremophiles :
a.
Thermus brockianus
b.
Deinicoccus radiodurans
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Chapter 2
The Extreme and Capabilities of Microbial Growth
ENV 411
PART A: DEFINITION
Please define the following terms:
Define the following:

Endolith

Halophile

Hyperthermophile

Hypolith

Lithoautotroph

Metalotolerant

Oligotroph

Osmophile

Piezophile

Polyextremophile

Psychrophile/Cryophile

Radioresistant

Thermophile

Xerophile
PART B: SHORT ANSWER
Answer the following questions:
1. Differentiate the different types of extremophiles
2. Explain adaptations of acidophiles and alkaliphiles
3. Discuss the value of extremophiles in nature and biotechnology
4. Identify the application of extremophiles in biotechnology
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The Extreme and Capabilities of Microbial Growth
ENV 411
Chapter 2
STUDY NOTES:
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