5. New branch of life....
In 1970s carl woese proposed -3
domain classification
Based on sequencing of 16s r RNA
The organism he revealed-the
achea..
Classifying Archaea remains
difficult, majority of these
organisms have never been
studied in the laboratory and
have only been detected by
analysis of their nucleic acids
in environmental samples.-
( metagenomics)
CCaarrll wwooeessee
6. Archaea are more wounderful than
you know...!
TThheerrmmooccooccccuuss
ggaammmmaattoolleerraannss –– aa ffllaaggeellllaattee
aarrcchhaaeeoonn tthhaatt tthhrriivveess iinn hhoott,,
ooxxyyggeenn--ssttaarrvveedd wwaatteerrss.. NNoottee tthhee
ttuufftt ooff ffllaaggeellllaa.. TThhiiss mmiiccrroobbee lliivveess
iinn wwaatteerr hhootttteerr tthhaann aabboouutt 116600FF
7. Property Archaea Bacteria Eukarya
Cell Membrane Ether-linked lipids,
pseudopeptidoglycan
Ester-linked lipids,
peptidoglycan
Ester-linked lipids, various
structures
Gene Structure
Circular chromosomes,
similar translation and
transcription to Eukarya
Circular chromosomes,
unique translation and
transcription
Multiple, linear
chromosomes, similar
translation and
transcription to Archaea
Internal Cell Structure No membrane-bound
organelles or nucleus
No membrane-bound
organelles or nucleus
Membrane-bound
organelles and nucleus
Metabolism[45]
Various, with
methanogenesis
unique to Archaea
Various, including
photosynthesis, aerobic
and anaerobic respiration,
fermentation, and
autotrophy
Photosynthesis and
cellular respiration
Reproduction Asexual reproduction,
horizontal gene transfer
Asexual reproduction,
horizontal gene transfer
Sexual and asexual
reproduction
Comparison to other domains
8. Introduction to the
AMrocrhpahoeloagy
Stain either Gram +ve or Gram –ve
Shapes – Spherical, rod, spiral, lobed, irregularly
shaped or pleomorphic
Single cells or filaments or aggregates, diameter
from 0.1 to over 15 μm
Multiplication – binary fission, budding,
fragmentation or other unknown mechanisms
CCoonnttdd……
10. Physiology
Aerobic, facultative and strictly anaerobic
Range from chemolithotrophs to organotrophs
Mesophilic & hyperthermophiles
Found in extreme environments
Few are symbionts in animal digestive system
eg- the marine archaean Cenarchaeum symbiosum lives
within (is an endosymbiont of) the sponge
Axinella mexicana.[180]
CCoonnttdd……
11. Archaeal cell envelopes
One of he distinctive feature of the
archaea is the nature of envelope
S-layer is the major component of the
cellwall
Some archaea lacks cellwall but have a
glyocalyx lying out side the cell membrane
Capsules and slime layers are rare among
archaea
13. Archael cellwall lacks peptidoglycan and exhibit
considerable variety in terms of their chemical
make up
The most common type of archaeal cell wall is an
S-layer composed of either protein or glycoprotein
the layer may be as thick as 20 to 40 nm.
eg; methanococcus, halobacterium
Other archaea have additional layers of material
outside the S-layer
methanospirillum has a protein sheath external to
the s-layer
methanosarcina has a layer of chondroitin- like
material, this material is called methanochondroitin
14. In some archaea S-layer is the outer most layer and
seperated from the plasma membrane by
pseudomurein
pseudomurein is a peptidogycan-like molecule.
differs from pepidoglycan in that it has N-acetyltalosaminuronic
acid instead of N-acetylmuramic
acid ,and beta (1 3)glycosidic
linkage insted of beta (1 4) glycosidic linkage.
eg- Methanobacterium, Methanothermus and
Methanopyrus
The last type of archael cellwall does not include
an s-layer .these archaea have a wall with a
single, homogenous layer resembling in gram-positive
bacteria
18. Archaeal plasma membranes
Archaeal membranes are composed primerly of lipids that
differ from bacterial and eukaryotic in two ways.
1. They contain hydrocarbons derived from isoprene units(five
carbon, branched)
2. Hydrocarbons attached to glycerol by ether linkage rather
than ester links
19. Archaeal phospholipids differ from those found in Bacteria and Eukarya in
two ways. First, they have branched phytanyl sidechains instead of linear
ones. Second, an ether bond instead of an ester bond connects the lipid to
the glycerol.
CCoonnttdd……
21. Genomes are significantly smaller than bacteria.
E. coli – 2.5 x 109 Daltons
T. acidophilum – 0.8 x 109 Daltons
Methanosarcina acetivorans,[116] the largest known
archaeal genome.
Nanoarchaeum equitans, the smallest archaeal genome
known;
plasmids are also found
Archaea usually have a single circular chromosome
22. Transcription and translation in archaea
resemble these processes in eukaryotes
more than in bacteria
Archaea have a single type of RNA
Polymerase and similar to eukaryotes
archaeal genes lack introns
Hyperthermophiles posses reverse DNA
gyrase
25. Archaea exhibit a great variety of chemical reactions in
their metabolism and use many sources of energy.
Some archaea obtain energy from inorganic compounds
such as sulfur or ammonia (they are lithotrophs). These
include nitrifiers, methanogens andanaerobic methane
oxidisers.
Other groups of archaea use sunlight as a source of
energy (they are phototrophs). However, oxygen–
generating photosynthesis does not occur in any of these
organisms.
26. CCoonnttdd……
archaea use a modified form of glycolysis (the
Entner–Doudoroff pathway) and either a complete or partial
citric acid cycle
Methanogenesis occcurs in the phylum Euryarchaeota
These reactions are common in gut-dwelling archaea
archaea use CO2 in the atmosphere as a source of carbon, in a
process called carbon fixation (they are autotrophs)
Archaeal energy sources are extremely diverse, and range from
the oxidation of ammonia by the Nitrosopumilales to the
oxidation of hydrogen sulfide or elemental sulfur by species of
Sulfolobus, using either oxygen or metal ions as electron
acceptors.
Phototrophic archaea use light to produce chemical energy in
the form of ATP
27. Autotrophy is widespread among methanogens & extreme
thermophiles
Thermoproteus & Sulfolobus – fix CO2 by reductive TCA cycle
Methanogens & extreme thermophiles –fix CO2 by reductive acetyl
coA p/w
Acetyl-CoA (Ljungdahl-Wood) pathway: A autotrophic CO2 fixing pathway
widespread in strict anerobes (e.g. methanogens, homoacetogens &
sulfatereducing bacteria).
Some methanogens can fix atmospheric nitrogen
Some stores glycogen has a storage form
CCoonnttdd……
28. Nutritional type Source of energy Source of carbon Examples
Phototrophs Sunlight Organic
compounds Halobacteria
Lithotrophs Inorganic
compounds
Organic
compounds or
carbon fixation
Ferroglobus,
Methanobacteria
or Pyrolobus
Organotrophs Organic
compounds
Organic
compounds or
carbon fixation
Pyrococcus,
Sulfolobus or
Methanosarcinales
Nutritio nal type s in aarrcchhaaeeaall mmeettaabboo lliissmm
30. Members of the domain Archaea are phylogenetically
divided into three kingdoms
Euryarchaeotoa
Crenarchaeota
Korarchaeota
• Phylogeny of domain Archaea based on comparision of
the 16S rRNAsequences.
Greek Archaios = ancient, primitive
Greek Eurus = wide(wide distribution);
Greek Crene = spring, fount (primary habitat).
Korarchiota = young man
33. Phylum Crenarchaeota
Most are extremely thermophilic & many are
acidophiles and S dependent
S – as electron acceptor or electron source by
lithotrophs
Almost all are strict anaerobes & grow in
geothermally heated water / soils that contain
elemental sulfur
CCoonnttdd……
34. Divided into one class – Thermoprotrei & three orders :
Thermoproteales
Sulfolobales
Desulfurococcales
Contain 69 genera – two of the better studied genera are
Thermoproteus & Sulfolobus
CCoonnttdd……
35. Sulfolobus
Gram –ve, aerobic, irregularly lobed spherical archaeons
Optimum temp.– 70 to 80 0C & optimum pH 2 - 3
hence also referred to as thermoacidophiles
Cell wall – lipoprotein & CH, lacks peptidoglycan
Grow lithotrophically on S granules in hot S springs oxidizing S to
Sulfuric acid
Oxygen Is the normal electron acceptor, Fe+3 may be used
CCoonnttdd……
36. Sugars & amino acids (glutamate) also serve as C & energy sources
CCoonnttdd……
37. Thermoproteus
Gram –ve, strictly anaerobic, hyperthermophilic long thin rod, can
be bent or branched
Cell wall consists of glycoprotein
Grows at temp. from 70 - 97 0C & pH 2.5 – 6.5
Found in hot springs & other hot aquatic habitats rich in sulfur
Can grow organotrophically & oxidize glucose, amino acids, alcohols
& organic acids with S
CCoonnttdd……
38. Grows chemolithtrophically using Hydrogen & S0
CO & CO2 can serve as the sole C source
An aquatic spring in Japan with
Thermoproteus growth
Thermoproteus
CCoonnttdd……
39. Phylum Euryarchaeota
Very diverse with 7 classes viz. Methanococcus,
Methanobacteria, Halobacteria, Thermoplasmata,
Thermococci, Archaeglobi & Methanopyri
Consists of 9 orders & 15 families
Includes methanogens, extreme halophiles, sulphate reducers
& many extreme thermophiles with S dependent metabolism
CCoonnttdd……
40. The Methanogens
Methanogenic bacteria are extremely oxygen
sensitive.
Methanogens require anaerobic conditions .
They are found in the digestive systems of
herbivores, marshes or lake bottoms, all sorts of mud
sediments and in man made anaerobic digestors in
sewage treatment plants.
They can be classified as Chemolithotrophic
methanogens and Methylotrophic methanogens.
Responsible for methanogenesis
41. Methanogenesis is the biological production of CH4 from either CO2
plus H2 or from methylated organic compounds.
A variety of unique coenzymes are involved in methanogenesis
chemolithotrophic methanogens that grow with CO2 plus H2
according to the equation:-
CO2 + 4H2 CH4 + 2H2O
Methylotrophic methanogens that grow with methyl group
containing substrates for eg. Methanol, methylamines, acetate
The reaction for acetate is:
CH3COOH CH4 + CH2
5 orders (Methanobacteriales, Methanococcales,
Methanomicrobiales, Methanosarcinales & Methanopyrales) & 26
genera
43. Methane formation from CO2 and H2 by Barker’s scheme.
The first carrier molecule is Methanofuran.
In a reaction that requires CO2 and reducing equivalents
it is converted to formylmethanofuran with the formyl
group residing at the aminomethyl group of the furan ring.
Transfer of the C1 moiety to tetrahydromethanopterin
and reduction of the formyl to methyl group follows.
It is finally transferred to the Coenzyme M and is reduced
to CH3 by the enzyme methyl co enzyme M
methylreductase
44. Diversity of Methanogens
Demonstrate diversity of cell wall
chemistries
Pseudomurein (e.g.,
Methanobacterium)
Methanochondroitin (e.g.,
Methanosarcina)
Protein or glycoprotein (e.g.,
Methanocaldococcus)
S-layers (e.g., Methanospirillum)
45.
46.
47. Some live autotrophically – acetyl coA from two molecules of CO2 &
then converting acetyl coA to pyruvate & other products
Found in anaerobic environment rich in organic matter
Rumen & intestine of animals, fresh water &
marine sediments, swamps & marshes, hot springs,
anaerobic sludge digesters & anaerobic protozoa
Ecological significance
Cow belches 200 – 400 ltrs CH4/day
Source of energy for sewage treatment plants
CCoonnttdd……
48. Yellowstone National Park
Ecological hazards
Methane gas – Greenhouse gas
Can oxidize Fe0
May contribute to corrosion of buried or submerged
iron pipes
M. thermoautotrophicum
CCoonnttdd……
49. The Halobacteria
Class Halobacteria – 15 genera in one family, the Halobacteriaceae
Aerobic chemoheterotrophs with respiratory metabolism
Non motile or motile by lophotrichous flagella
Absolutely dependent on high NaCl conc.
At least 1.5 M NaCl, growth optimum at 3 – 4 M
Cell wall disintegrates below 1.5 M conc.
Grow only in high salinity habitats
Cause spoilage of salted fish
CCoonnttdd……
50. E.g. Halobacterium salinarium
Unusual type of photosynthesis
On exposure to sunlight – purple membrane – bacteriorhodopsin
Four types of rhodopsins
Bacteriorhodopsin – proton transport for ATP
synthesis
Halorhodopsin – uses light energy to transport
chloride ions into the cell & maintains KCl conc.
Remaining two – photoreceptors, one for red light
& one for blue
CCoonnttdd……
52. The Thermoplasms
archaea lack cell wall
Class Thermoplasmata
Two genera, Thermoplasma & Pichrophilus
Thermoplasma
Grows in refuse piles of coal mines
Temperatures from 55 – 590C & pH 1-2
Plasma membrane is strengthened by large
quantities of diglycerol, tetraethers,
lipopolysaccharides & glycolipids
DNA stabilized by nucleosomes
CCoonnttdd……
53. At 590C - irregularly shaped & at lower
temperatures – spherical
May be motile by flagella
CCoonnttdd……
54. Picrophilus
Lacks cell wall , has S layer outside PM
Aerobic, irregularly shaped cocci, 1 – 1.5 μm in
diameter
Temp. range 47 – 650C, optimum temp. 600C
pH below 3.5, optimum pH 0.7
Can grow at pH 0
CCoonnttdd……
55. Extremely Thermophilic S0
Metabolizers
Class Thermococci, order Thermococcales
Strictly anaerobic
Reduce sulfur to sulfide
Motile by flagella
Optimum growth temp. 88 –1000C
Two genera, Thermococcus & Pyrococcus
CCoonnttdd……
56. Sulfate Reducing Archaea
Class Archaeglobi, order Archaeoglobales
Gram –ve, irregular coccoid cells
Cell wall – glycoprotein subunits
Electron sources – hydrogen, lactate & glucose, reduce sulfate,
sulfite or thiosulfate to sulfide
S is not used as electron acceptor
Extremely thermophilic, optimum temp. around 830C, occur in
hydrothermal vents
CCoonnttdd……
58. Methanogens are used for the production of methane which is a rich
source of energy (bio gas)
Methanogenic archaea are a vital part of sewage treatment
Halophilic archaea are used to prescreen antitumor drugs active on
eukaryotic proteins
Thermophilic archaea are used in PCR
thermostable DNA polymerases, such as the Pfu DNApolymerase
from Pyrococcus furiosus,
amylases,galactosidases and pullulanases in other species
of Pyrococcus that function at over 100 °C (212 °F) allow food
processing at high temperatures, such as the production of
lactose milk and whey
In mineral processing, acidophilic archaea display promise for the
extraction of metals from ores, including gold, cobalt and copper.
59. References
Prescott, Lansing M.; Harley, John P. and Klein, Donald
A.,2003. Microbiology, 5th edition. McGraw – Hill
www.euarch.blogspot.com
www.filebox.vt.edu
www.nature.com/ntmicro/journal/v5/n4
www.fib_tab/nrmicro1619_F3.html
www.microbewiki.kenyon.edu/
