5.DNA sequencing - University

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BIO TECHNOLOGY

5mark

1. Applications

of bio technology

Biotechnology has applications in four major industrial areas, including health care (medical),
crop production and agriculture, non food (industrial) uses of crops and other products (e.g.
biodegradable plastics
,
vegetable oil
,
biofuels
), and environmental uses.

For example, one application of biotechnology is the directed use of
organisms

for the
manufacture of organic products (examples inclu
de
beer

and
milk

products). Another example is
using naturally present
bacteria

by the mining industry in
bioleaching
. Biotechnology is also
used to recycle, treat waste, cleanup sites contaminated by industrial activities (
bioremediation
),
and also to produce
biological weapons
.

A series of derived terms have been coined to identify se
veral branches of biotechnology; for
example:



Bioinformatics

is an interdisciplinary field which addresses biological problems using
computational techniques, and makes the rapid organization and analysis of biological
data possible. The field may also be referred to as
computational biology
, and can be
defined as,

"conceptualizing biology in terms of molecules and then applying informatics
techniques to understand and organize the information associated with these molecules,
on a large scale."
[17]

Bioinformatics plays a key role in various areas, such as
functional
genomics
,
structural genomics
, and
proteomics
, and forms a key component in the
biotechnology and pharmaceutical sector.



Blue biotechnology

is a term that has been used to describe the marine and aquatic
applications of biotechnology, but its use is relatively rare.



Green biotechnology

is biotechnology applied to
agricultural

processes. An example
would be the selection and domestication of plants via
micropropagation
. Another
example is the designing of
transgenic plants

to grow under specific environments in th
e
presence (or absence) of chemicals. One hope is that green biotechnology might produce
more environmentally friendly solutions than traditional
industrial agr
iculture
. An
example of this is the engineering of a plant to express a
pesticide
, thereby ending the
need of external application of pesticides. An example of this would be
Bt corn
. Whether
or not green biotechnology products such as this are ultimately more environmentally
friendly is a topic of considerable debate.



Red biotechnology

is applied to
medical

processes. Some examples are the designing of
organisms to produce
antibiotics
, and the engineering of genetic cures through
genetic
manipulation
.



White biotechnology
, also known as industrial biotechnology, is biotechnology applied
to
industrial

processes. An example is the designing of an organism to produce a useful
chemical. Another example is the using of
enzymes

as industrial
catalysts

to either
produce valuable chemicals or destroy hazardous/polluting chemicals. White
biotechnology tends to consume less in resources than traditional processes used to
produce industrial goods.{{Citation needed|date=October 2009}

http://www.bio
-
entrepreneur.net/Advance
-
definition
-
biotech.pdf}

The investment and economic output of all of these types of applied biotechnologies is termed as
bioeconomy
.

2. Genetic

testing

Genetic testing

involves the direct examination of the
DNA

molecule itself. A scientist scans a
patient's DNA sample for mutated sequences.

There are two major types of gene tests. In the first type, a researcher may design short pieces of
DNA ("probes") whose sequences are comple
mentary to the mutated sequences. These probes
will seek their complement among the base pairs of an individual's genome. If the mutated
sequence is present in the patient's genome, the probe will bind to it and flag the mutation. In the
second type, a res
earcher may conduct the gene test by comparing the sequence of DNA bases in
a patient's gene to disease in healthy individuals or their progeny.

Genetic testing is now used for:



Carrier screening, or the identification of unaffected individuals who carry o
ne copy of a gene
for a disease that requires two copies for the disease to manifest;



Confirmational diagnosis of symptomatic individuals;



Determining sex;



Forensic/identity testing;



Newborn screening;



Prenatal diagnostic screening;



Presymptomatic

testing for estimating the risk of developing adult
-
onset cancers;



Presymptomatic testing for predicting adult
-
onset disorders.

Some genetic tests are already available, although most of them are used in developed countries.
The tests currently available
can detect mutations associated with rare genetic disorders like
cystic fibrosis
,
sickle cell anemia
, and
Huntington's disease
. Recently, tests have been developed
to detect mutation for a handful of more complex conditions such as breast, ovar
ian, and colon
cancers. However, gene tests may not detect every mutation associated with a particular
condition because many are as yet undiscovered.

3. Bacteriophage

genomics

B
acteriophages

have played and continue to play a key role in bacterial
genetics

and
molecular
biology
.

Historically, they were used to define
gene

structure and gene regulation. Also the first
genome

to be sequenced was a
bacteriophage
. However, bacteriophage research did not lead the
genomics revolution, which is clearly dominated by bacterial genomics. Only very recently has
the study of bacteriophage genom
es become prominent, thereby enabling researchers to
understand the mechanisms underlying
phage

evolution. Bacteriophage genome sequences can
be obtained through direct sequencing of isolated ba
cteriophages, but can also be derived as part
of microbial genomes. Analysis of bacterial genomes has shown that a substantial amount of
microbial DNA consists of
prophage

sequences and pr
ophage
-
like elements. A detailed database
mining of these sequences offers insights into the role of prophages in shaping the bacterial
genome.
[14]

Cyanobacteria genomics

At present there are 24
cyanobacteria

for which a total genome sequence is available. 15 of these
cyanobacteria come from the marine environment. These are six
Prochlorococcus

strains, seven
marine
Synechococcus

strains,
Trichodesmium erythraeum

IMS101 and
Crocosphaera watsonii

WH8501
. Several studies have demonstrated how these sequences could be used ve
ry
successfully to infer important ecological and physiological characteristics of marine
cyanobacteria. However, there are many more genome projects currently in progress, amongst
those there are further
Prochlorococcus

and marine
Synechococcus

isolates,
Acaryochloris

and
Prochloron
, the N
2
-
fixing filamentous cyanobacteria
Nodularia spumigena
,
Lyngbya aestuarii

an
d
Lyngbya majuscula
, as well as
bacteriophages

infecting marine cyanobaceria
. Thus, the
growing body of genome information can also be tapped in a more general way to address global
problems by applying a comparative approach. Some new and exciting examples of progress in
this field are the identification of genes for regulatory R
NAs, insights into the evolutionary
origin of
photosynthesis
, or estimation of the contribution of horizontal gene transfer to the
genomes that have been analyzed.
[15]

20MARK

4.Nucleotides


Chemical structure of RNA

Nucleic acids consist of a chain of linked units called nucleotides. Each nucleotide consists of
three subunits: a
phosphate

group and a
sugar

(
ribose

in the case of
RNA
,
deoxyribose

in
DNA
)
make up the backbone of the nucleic acid strand, and attached to the s
ugar is one of a set of
nucleobases
. The nucleobases are important in
base pairing

of strands to form higher
-
level

secondary

and
tertiary
structure

such as the famed
double helix
.

The possible letters are
A
,
C
,
G
, and
T
, representing the four
nucleotide

bases

of a DNA strand


adenine
,
cytosine
,
guanine
,
thymine



covalently

linked to a
phosphodiester

backbone. In the
typical case, the sequences are printed abutting one another without gaps, as in the sequence
AAAGTCTGAC, read left to ri
ght in the
5' to 3'

direction. With regards to
transcription
, a
sequence is on the coding strand if it has the same order as the transcribed RNA.

One sequence can be
complementary

to another sequence, meaning that they have the base on
each position is the complementary (i.e. A to T, C to G) and in the reverse order. For example,
the complementary sequence to TTAC is GTAA. If one strand of the double
-
stranded DNA

is
considered the
sense

strand, then the other strand, considered the antisense strand, will have the
complementary sequence to the sense strand.

Not
ation

While A, T, C, and G represent a particular nucleotide at a position, there are also letters that
represent ambiguity which are used when more than one kind of nucleotide could occur at that
position. The rules of the International Union of Pure and
Applied Chemistry (
IUPAC
) are as
follows:
[1]



A

= adenine



C

= cytosine



G

= guanine



T

= thymine



R

= G A (purine)



Y

= T C (pyrimidine)



K

= G T (keto)



M

= A C (amino)



S

= G C (strong bonds)



W

= A T (weak bonds)



B

= G T C (all but A)



D

= G A T (all but C)



H

= A C T (all but G)



V

= G C A (all but T)



N

= A G C T (any)

These symbols are also valid for RNA, except with U (ur
acil) replacing T (thymine).
[1]

Apart from adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U), DNA and RNA
also contain bases that have been modified after the

nucleic acid chain has been formed. In DNA,
the most common modified base is
5
-
methylcytidine

(m5C). In RNA, there are many modified
bases, including pseudouridine (Ψ), di
hydrouridine (D), inosine (I), ribothymidine (rT) and
7
-
methylguanosine

(m7G).
[2]
[3]

Hypoxanthine

and
xanthine

are two of the many bases created
through
mutagen

presence, both of them through deamination (replacement of the amine
-
group
with a carbonyl
-
group). Hypoxanthine is produced from
adenine
, xanthine from
guanine
.
[4]

Similarly, deamination o
f
cytosine

results in
uracil
.

5.DNA sequencing

DNA sequencing

is the process of determining the precise order of
nucleotides

within a
DNA

molecule. It includes any method or technology that is used to determine the order of the four
bases

adenine
,
guanine
,
cytosine
, and
thymine

in a strand of DNA. The advent of rapid DNA
sequencing methods has greatly accelerated biological and medical research and discovery.

Knowledge of DNA sequences has become indispensable for basic biological research
, and in
numerous applied fields such as diagnostic,
biotechnology
,
forensic biology
, and biological
systematics
. The rapid speed of sequencing attained with modern DNA sequencing technology
has been instrumental in the sequencing of complete DNA sequences, or
genomes

of numerous
types and species of life, including the
human genome

and other complete DNA sequences of
many anim
al, plant, and
microbial

species.

The first DNA sequences were obtained in the early 1970s by academic researchers using
laborious methods based on
two
-
dimensional chromatography
. Following the development of
fluorescence
-
based sequencing methods with
automated analysis
,
[1]

DNA sequencing has
become easier and orders of magnitude faster.
[2]

Use of sequencing

DNA sequencing may be used to determine the sequence of individual
genes
, larger genetic
regions (i.e. c
lusters of genes or
operons
), full chromosomes or entire genomes. Depending on
the methods used, sequencing may provide the order of nucleotides in DNA or RNA isolated
from cells of animals,

plants, bacteria,
archaea
, or virtually any other source of genetic
information. The resulting sequences may be used by researchers in
molecular biology

or
genetics

to further scientific progress or may be used by medical personnel to make treatment
decisions.

History

Though the structure of DNA was established as a
double helix

in 1953,
[3]

several
decades would
pass before fragments of DNA could be reliably analyzed for their sequence in the laboratory.
RNA sequencing was one of the earliest forms of nucleotide sequencing. The major landmark of
RNA sequencing is the sequence of the first complete ge
ne and the complete genome of
Bacteriophage MS2
, identified and published by
Walter Fiers

and
his coworkers at the
University of Ghent

(
Ghent
,
Belgium
), between 1972
[4]

and 1976.
[5]

Several notable advancements in DNA sequencing were
made during the 1970s.
Frederick
Sanger

developed rapid DNA sequencing methods at the
MRC Centre
,
Cambridge
, UK and
published a method for "DNA sequencing with chain
-
terminating inhibitors" in 1977.
[6]

Walter
Gilbert

and
Allan Maxam

at
Harvard

also developed sequencing methods, including one for
"DNA sequencing by chemical degradation".
[7]
[8]

In 1973, Gilbert and Maxam reported the
sequence of 24 basepairs using a method known as wandering
-
spot analysis.
[9]

Advancements in
sequencing were aided by the concurrent development of
recombinant DNA

technology,
allowing DNA samples to be iso
lated from sources other than viruses.

The first full DNA genome to be sequenced was that of
bacteriophage φX174

in 1977.
[10]

Medical Research Council

scientists deciphered the complete DNA sequence of the
Epstein
-
Barr
virus

in 1984, finding it to be 170 thousand base
-
pairs long.

Leroy E. Hood
's laboratory at the
California Institute of Technology

and Smith announced the
first semi
-
automated DNA sequencing machine in 1986.
[
citation needed
]

This was followed by
Applied Biosystems
' marketing of the first fully automated sequencing machine, the ABI 370, in
1987. By 1990, the U.S.
National Institutes of Health

(NIH) had begun

large
-
scale sequencing
trials on
Mycoplasma capricolum
,
Escherichia coli
,
Caenorhabditis elegans
, and
Saccharomyces
cerevisiae

at a cost
of US$0.75 per base. Meanwhile, sequencing of human
cDNA

sequences
called
expressed sequence tags

be
gan in
Craig Venter
's lab, an attempt to capture the coding
fraction of the
human genome
.
[11]

In 1995, Venter,
Hamilton Smith
, and colleagues at
The
Institute for Genomic Research

(TIGR) published the first complete genome of a free
-
living
organism, the bacterium
Haemophilus influenzae
. The circular chromosome contains 1,830,137
bases and its publication in the journal Science
[12]

marked the first published use of whole
-
genome shotgun sequencing, eliminating the need for initial mapping efforts. By 2001, shotgun
sequencing methods had been used to produce a draft sequence of the human genome.
[13]
[14]

Several new methods for DNA sequencing were developed in the mid to late 1990s. These
techniques comprise

the first of the "next
-
generation" sequencing methods. In 1996,
Pål Nyrén

and his student
Mos
tafa Ronaghi

at the Royal Institute of Technology in
Stockholm

published
their method of
pyrosequencing
.
[15]

A year later, Pascal Mayer and Laurent Farinelli submitted
patents to the World Intellectual Property Organization describing DNA colony sequencing.
[16]

Lynx Therapeutics published and marketed "
M
assively parallel signature sequencing
", or MPSS,
in 2000. This method incorporated a parallelized, adapter/ligation
-
mediated, bead
-
based
sequencing technology and served as the first commercially
-
available "next
-
generation"
sequencing method, though no
DNA sequencers

were sold to independent laboratories.
[17]

In
2004,
454 Life Sciences

marketed a parallelized version of pyrosequencing.
[18]
[19]
The first
version of their machine reduced sequencing costs 6
-
fold compared to automated Sanger
sequencing, and was the second of the new generation of sequencing technologies, after
MPSS.
[20]

The large quantities of data produced by DNA sequencing have also required development of
new methods and programs for sequence analysis. Phil Green and Brent Ewing of the Univ
ersity
of Washington described their
phred quality score

for sequencer data analysis in 1998

6. Immunology

Immunology

is a branch of
biomedical

science

that covers the study of all aspects of the
immune system

in all
organisms
.
[1]

It deals with the
physiological

functioning of the immune
system in states of both health and diseases; malfunctions of the immune system in
immunological disorders (
autoimmune diseases
,
hypersensitivities
,
immune deficienc
y
,
transplant rejection
); the physical, chemical and physiological characteristics of the components
of the immune system
in vitro
,
in situ
, and
in vivo
. Immunology has applications in several
disciplines of science, and

as such is further divided.

Even before the concept of
immunity

(from
immunis
,
Latin

for "exempt") was developed,
numerous early physicians characterized organs that would later prove to be part of the immune
system. The key primary lymphoid organs of the immune system are the
thymus

and
bone
marrow
, and secondary lymphatic tissues such as
spleen
,
tonsils
,
lymph vessels
,
lymph nodes
,
adenoids
, and
skin

and liver. When health conditions warrant, immune system organs including
the thymus, spleen, portions of bone marrow, lymph nodes and secondary lymphatic

tissues can
be
surgically

excised for examination while patients are still alive.

Many components of the immune system are actually
cellular

in nature and not associated with
any specific organ but rather are embedded or circulating in various
tissues

located throughout
th
e body.

Classical immunology

Classical immunology ties in with the fields of
epidemiology

and
medicine
. It studies the
relationship between the body systems,
pathogens
, and immunity. The earliest written mention of
immunity can be traced back to the
plague

of
Athens

in 430 BCE.
Thucydides

noted that people
who had recovered from a previous
bout of the disease could
nurse

the sick without contracting
the illness a second time. Many other ancient societies have references to this phenomenon, but it
was not until the 19th and 20th ce
nturies before the concept developed into scientific theory.

The study of the molecular and cellular components that comprise the immune system, including
their function and interaction, is the central science of immunology. The immune system has
been divi
ded into a more primitive
innate immune system
, and
acquired or adaptive immune
system

o
f vertebrates, the latter of which is further divided into
humoral

and
cellu
lar
components
.

The humoral (antibody) response is defined as the interaction between
antibodies

and
antigens
.
Antibodies
are specific proteins released from a certain class of immune cells (B
lymphocytes
).
Antigens are defined as anything that elicits generation of antibodies, hence they are
Anti
body
G
en
erators. Immunology itself rests on an understanding of the properties of these two
biological entities. However, equally important is the cellular response, which can not only kill
infected cells in its own right, but is also crucial in controlling the
antibody response. Put simply,
both systems are highly interdependent.

In the 21st century, immunology has broadened its horizons with much research being performed
in the more specialized niches of immunology. This includes the immunological function of
c
ells, organs and systems not normally associated with the immune system, as well as the
function of the immune system outside classical models of immunity (Yemeserach 2010).

Clinical immunology

Clinical immunology is the study of
diseases

caused by disorders of the immune system (failure,
aberrant action, and malignant growth of the cellular elements of the system). It also involves
diseases of other systems, where immune reactions play a part in the pathology and clinical
features.

The di
seases caused by disorders of the immune system fall into two broad categories:
immunodeficiency
, in which parts of the immune system fail to provide an adequate response
(
examples include
chronic granulomatous disease
), and
autoimmunity
, in
which the immune
system attacks its own host's body (examples include
systemic lupus erythematosus
,
rheumatoid
arthritis
,
Hashimoto's disease

and
myasthenia gravis
). Other immune system disorders include
different
hypersensitivities
, in which the system responds inappropriately to harmless
compounds (
asthma

and other
allergies
) or responds too intensely.

The most well
-
known disease that affects the immune system itself is
AIDS
, caused by
HIV
.
AIDS is an im
munodeficiency characterized by the lack of CD4+ ("helper")
T cells
,
dendritic
cells

and
macrophages
, which are destroyed by HIV.

Clinical immunologists also study ways to prevent
transplant rejecti
on
, in which the immune
system attempts to destroy
allografts
.

Developmental immunology

The body’s capability to react to antigen depends on a person's age, antigen type, maternal
factor
s and the area where the antigen is presented.
[2]

Neonates

are said to be in a state of
physiological immunodeficiency, because both their innate and adaptive immunological
responses are greatly suppressed. Once born, a child’s immune system responds favorably to
protein antigens while not as well to glycoprotein
s and polysaccharides. In fact, many of the
infections acquired by neonates are caused by low virulence organisms like
Staphylococcus

and
Pseudomonas
. In neonates, opsonic activity and the ability to activate the
complement cascade

is
very limited. For example, the mean

level of C3 in a newborn is approximately 65% of that
found in the adult. Phagocytic activity is also greatly impaired in newborns. This is due to lower
opsonic activity, as well as diminished up
-
regulation of
integrin

and
selectin

receptors, which
limit the ability of neutrophils to interact with adhesion molecules in the endothelium. Their
monocytes are slow and have a r
educed ATP production, which also limits the newborns
phagocytic activity. Although, the number of total lymphocytes is significantly higher than in
adults, the cellular and humoral immunity is also impaired. Antigen presenting cells in newborns
have a red
uced capability to activate T cells. Also, T cells of a newborn proliferate poorly and
produce very small amounts of
cytokines

like IL
-
2, IL
-
4, IL
-
5, IL
-
12, and IFN
-
g which limits
their ca
pacity to activate the humoral response as well as the phagocitic activity of macrophage.
B cells develop early in gestation but are not fully active.
[3]



Monocytes: An Arti
st's Impression

Maternal factors also play a role in the body’s immune response. At birth most of the
immunoglobulin

is present is maternal IgG. Because IgM, IgD, IgE and IgA d
on’t cross the
placenta, they are almost undetectable at birth. Although some IgA is provided in breast milk.
These passively acquired antibodies can protect the newborn up to 18 months, but their response
is usually short
-
lived and of low affinity.
[3]

These antibodies can also produce a negative
response. If a child is exposed to the antibody for a particular antigen before being exposed to the
antigen itself then the child wil
l produce a dampened response.
Passively acquired maternal
antibodies

can suppress the antibody response to active immunization. Similarly the response of
T
-
cells to vaccin
ation differs in children compared to adults, and vaccines that induce Th1
responses in adults do not readily elicit these same responses in neonates.
[3]

By 6
-
9 months after
bi
rth, a child’s immune system begins to respond more strongly to glycoproteins. Not until 12
-
24
months of age is there a marked improvement in the body’s response to polysaccharides. This
can be the reason for the specific time frames found in vaccination s
chedules.
[4]
[5]

During adolescence the human body undergoes several physical, physiological and
immunological changes. These changes are started and mediated by different
hormones
.
Depending on the sex eith
er
testosterone

or
17
-
β
-
oestradiol
, act on male and female bodies
accordingly, start acting at ages of 12 and
10 years.
[6]

There is evidence that these steroids act directly not only on the primary and secondary sexual
characteristics, but also have an effect on the development and

regulation of the immune
system.
[7]

There is an increased risk in developing autoimmunity for pubescent and post pubescent females
and males.
[8]

There is also some evidence that cell surface receptors on B cells and macrophages
may detect sex hormones in the system.
[9]

The female sex hormone 17
-
β
-
oestradiol has been shown to regulate the level of immunological
response.
[10]

Similarly, some male
androgens
, like testosterone, seem to suppress the stress
response to infection; but other androgens like DHEA have the opposite effect, as it increases the
immune response instead of down playing it.
[11]

As in females, the male sex hormones seem to
have more control of the immune system during puberty and the time right after than in fully
developed adults. Other than hormonal ch
anges physical changes like the involution of the
Thymus during puberty will also affect the immunological response of the subject or patient.
[12]

Immunotherapy

The use
of immune system components to treat a disease or disorder is known as
immunotherapy. Immunotherapy is most commonly used in the context of the treatment of
cancers

together with
chemotherapy

(
drugs
) and
radiotherapy

(
radiation
). However,
immunotherapy is also often used in the immunosuppressed (such as
HIV

patient
s) and people
suffering from other immune deficiencies or autoimmune diseases.

Diagnostic immunology

The specificity of the bond between antibody and antigen has made it an excellent tool in the
detection of substances in a variety of diagnostic techniques
. Antibodies specific for a desired
antigen

can be conjugated with a radiolabel, fluorescent label, or color
-
forming enzyme and are
used as a "probe" to detect it. However, the similarity be
tween some antigens can lead to false
positives and other errors in such tests by antibodies cross
-
reacting with antigens that aren't exact
matches.
[13]

Evolutionary immu
nology

Study of the immune system in
extant species

is capable of giving us a key understanding of the
evo
lution

of species and the immune system.

Different types of organisms have different types of immune systems: single
-
celled organisms
use
phagocytosis
;
arthropods

use circulating
antimicrobial peptides
; and
vertebrates

use both the
aforementioned methods as well as
lymphatic systems
. Every organism living today has an
immune system that has evolved to be capable of pr
otecting it from most forms of harm; those
organisms that did not adapt their immune systems to external threats are no longer around to be
observed.

Insects

and other
arthropods
, while not possessing true adaptive immunity, show highly evolved
systems of innate immunity, and are additionally protected from external injury (and exposure to
pathogens) by their
chitinous

shells.
Plants

also use forms of innate immunity.
[14]

Reproductive immunology

This area of the immunology is devoted to the study of immunological aspects of the
reproductive process including fetus acceptance. The term has also been used by fertility clinics
to address fertility problems, recurrent miscarria
ges, premature deliveries, and dangerous
complications such as
pre
-
eclampsia
.

7.Habitats and ecology

Microorganisms are found in almost every
habitat

present in nature. Even in hostile
environments such as the
poles
,
deserts
,
geysers
,
rocks
, and the
deep sea
. Some types of
microorganisms have adapted to the extreme conditions and sustained colonies; these organisms
are known as
extremophiles
. Extremophiles ha
ve been isolated from rocks as much as 7
kilometres below the Earth's surface,
[50]

and it has been suggested that the amount of living
organisms below the Earth's surface may be comparable with the amount of life on or above the
surface.
[28]

Extremophiles
have been known to survive for a prolonged time in a
vacuum
, and can
be highly resistant to
radiat
ion
, which may even allow them to survive in space.
[51]

Many types
of microorganisms have intimate
symbiotic

relationships with other larger organisms; some of
which are mutually beneficial (
mutualism
), while others can be damaging to the
host

organism
(
parasitism
). If microorganisms can cause
disease

in

a host they are known as
pathogens
.

Extremophiles

Extremophiles

are microorganisms that have adapted so that
they can survive and even thrive in
conditions that are normally fatal to most life
-
forms. For example, some species have been found
in the following extreme environments:



Temperatur
e
: as high as 130 °C (266

°F),
[52]

as low as −17 °C (1

°F)
[53]



Acidity
/
alkalinity
: less than
pH

0,
[54]

up to pH 11.5
[55]



Salinity
: up to saturation
[56]



Pressure
: up to 1,000
-
2,000
atm
, dow
n to 0 atm (e.g.
vacuum

of
space
)
[57]



Radiation
: up to 5k
Gy
[58]

Extremophiles are significant in different ways. They extend terrestrial life into much of the
Earth's
hydrosphere
,
crust

and atmosphere, their specific evolutionary adaptation mechanisms to
their extreme environment can be exploited in
bio
-
technology
, and their very existence under
such extreme conditions increases the potential for
extraterrestrial life
.
[59]

Soil microbes

The
nitrogen cycle

in soils depends on the
fixati
on of atmospheric nitrogen
. One way this can
occur is in the nodules in the roots of
legumes

that contain symbiotic
bacter
ia

of the genera
Rhizobium
,
Mesorhizobium
,
Sinorhizobium
,
Bradyrhizobium
, and
Azorhizobium
.
[60]

Symbiotic microbes

Symbiotic

microbes such as fungi and algae form an association in
lichen
. Certain fungi form
mycorrhizal

symbioses with trees that increase the supply of nutrients to the tree.