Brief description about : Diversity Euryarchaeota Crenarchaeota and more : Extremely Halophilic Archaea

2. Archaea
Brief description about :
Diversity
Euryarchaeota
Crenarchaeota
and more :
Extremely Halophilic Archaea
Supervisor: Dr Doodi
Presented by: Nima eslamnezhad

3. We now consider organisms in the domain Archaea.
Some major characteristics of Archaea include the absence of peptidoglycan
in cell walls and the presence of ether-linked lipids and structurally complex
RNA polymerases.
Reminder

4. Phylogenetic tree 16s rRNa
Phylogenetic and Metabolic Diversity of Archaea
Diversity
The separation of these groups is also supported by genomic analyses, which show
that each group has its own pattern of genes but also that they share many genes in
common.
Euryarchaeota
Crenarchaeota

5. Crenarchaeota
Laboratory culture
mostly hyperthermophiles
Inhabit aquatic and terrestrial environments
mostly chemolithotrophic autotrophs
Primary producers in these habitats
Hyperthermophilic species of Crenarchaeota tend to cluster closely
together and occupy short branches on the phylogenetic tree
These organisms are therefore thought to be more slowly evolving than
other lineages in the domain.
best available models of “early” Archaea (early life forms in general

6. Euryarchaeota
Cold-dwelling relatives of hyperthermophilic crenarchaeotes in the oceans
and various other temperate and even polar environments, a From a
phylogenetic perspective, these species occupy longer branches on the tree
and have therefore undergone rapid evolution, probably in the transition
from hot to colder environments.
:This phylum includes
methanogens and
several genera of extremely halophilic Archaea “halobacteria”
and Hyperthermophiles : Thermococcus and Pyrococcus and the
methanogen
Methanopyrus, all of which branch near the root of the archaeal tree
The cell wall–less Thermoplasma, an organism phenotypically similar tothe
mycoplasmas also exist.
In parallel to the Crenarchaeota, a large group of thus far uncultured euryarchaeotes
inhabits marine environments and occupies long branches near the top of the archaeal
tree.

7. Metabolic Diversity of Archaea
Chemoorganotrophic
Chemolithotrophic
No true phototrophic species containing
chlorophyll pigments are known, although a
unique lightmediated
form of energy generation does occur in some
halophilic species
Energy metabolism in methanogens is
unlike that of any other microbial group
(Bacteria or Archaea)
(CH4) is produced in either an
anaerobic respiration where carbon
dioxide (CO2) is the electron
acceptor and hydrogen (H2) is the
electron donor, or from the
catabolism of a short list of organic
compounds, acetate being the
prime example.
Autotrophy is widespread in the Archaea and proceeds by several different pathways :
The acetyl-CoA pathway or some slight modification of it
Reverse (reductive) citric acid cycle
The 3-hydroxypropionate/4-hydroxypropionate cycle
.Enzymes of the Calvin cycle also been detected

8. Euryarchaeota
Key Genera:
Halobacterium
Haloferax
Natronobacterium
Extremely Halophilic Archaea
called the “haloarchaea,” are a diverse group that inhabits environments high in salt.
Naturally salty environments: solar salt evaporation ponds and
salt lakes
artificial saline habitats such as the surfaces of heavily salted foods
for example: certain fish and meats.

9. The term extreme halophile is used to indicate that these
organisms are not only halophilic, but that their requirement for
salt is very high, in some cases at levels near saturation.
An organism is considered an extreme halophile if it requires 1.5 M (about
9%) or more sodium chloride (NaCl) for growth. Most species of extreme
halophiles require 2–4 M NaCl (12–23%) for optimal growth. Virtually all
extreme halophilescan grow at 5.5 M NaCl (32%, the limit of saturation for
NaCl), although some species grow very slowly at this salinity.
Haloferax and Natronobacterium, are able to grow at much lower salinities,
such as at or near that of seawater (about 2.5% NaCl).

10. Hypersaline Environments:Chemistry and Productivity
Hypersaline habitats are common throughout the world, but extremely hypersaline
habitats are rare.
The predominant ions in a hypersaline lake depend on the
Surrounding topography
Geology
General climatic conditions.
for example:
Great Salt Lake in Utah (USA) is
essentially concentrated seawater; the
relative proportions of the
various ions are those of seawater,
although the overall concentration
of ions is much higher. Sodium (Na+) is
the predominant
cation in Great Salt Lake, whereas chloride
(Cl–) is the predominant
anion; significant levels of sulfate are also
present at a
slightly alkaline pH (Table 19.1).

11. Archaea are not the only microorganisms present in this environments The
eukaryotic alga Dunaliella
anoxygenic phototrophic purple bacteria of the genera Ectothiorhodospira
Halorhodospira
a few extremely halophilic chemoorganotrophic Bacteria:
Halanaerobium
Halobacteroides
Salinibacter
Soda lakes are highly alkaline, hypersaline environments. The water chemistry
of soda lakes resembles that of hypersaline lakes such as Great Salt Lake, but
because high levels of carbonate minerals are also present in the surrounding
strata, the pH of soda lakes is quite high.

13. Bloom of halophilic microorganisms. Dense growth of halophilic
microorganisms in hypersaline environments leads to reddening of
the brine. Photo Dr. S. DasSarma.

14. Taxonomy and Physiology of Extremely Halophilic Archaea

15. The term haloarchaea,these Archaea are commonly called “halobacteria,”
because the genus Halobacterium was the first in this group to be described
and is still the best-studied representative of the group.
Natronobacterium & Natronomonas
Haloarchaea stain gram-negatively
reproduce by binary fission
do not form resting stages or spores
Cells of the various cultured genera are
Rod-shaped
Cocci
Cup-shaped,
but even cells that form squares are
known (Figure 19.2d).
i
p
h
i
l
i
c
&
H
a
l
o
p
h
i
l
i
c
Alkaliphilic
&
Halophilic
A square isolate was recently obtained
in pure culture and named
Haloquadratum

16. The genomes of Halobacterium and Halococcus are unusual in that
large plasmids containing up to 30% of the total cellular DNA are
present and the GC base ratio of these plasmids (near 60% GC)
differs significantly from that of chromosomal DNA (66–68%GC).
Water Balance in Extreme Halophiles
Most species of extremely halophilic Archaea are obligate aerobes.
Most halobacteria use amino acids or organic acids as energy sources and
require a number of growth factors (mainly
Vitamins for optimal growth.
Extremely halophilic Archaea require large amounts of Na+ for growth, typically
supplied as NaCl.
Detailed salinity studies of Halobacterium have shown that the requirement for
Na+ cannot be satisfied by any other ion (K+)
However, cells of Halobacterium need both Na+ and K+ for growth, because
each plays an important role in maintaining osmotic balance.

17. To do so in a high-solute environment such as the salt-rich habitats of
Halobacterium, organisms must either accumulate or synthesize solutes
intracellularly. These solutes are called compatible solutes. These
compounds counteract the tendency of the cell to become dehydrated under
conditions of high osmotic strength by placing the cell in positive water
balance with its surroundings.
Cells of Halobacterium, however, do not synthesize or accumulate
organic compounds but instead pump large amounts of K+ from the
environment into the cytoplasm. This ensures that the concentration
of K+ inside the cell is even greater than the concentration
of Na+ outside the cell .
This ionic condition maintains positive water balance

18. The Halobacterium cell wall is composed of glycoprotein and is stabilized by
Na+. Sodium ions bind to the outer surface of the Halobacterium wall and are
absolutely essential for maintaining cellular integrity.
When insufficient Na+ is present, the cell wall breaks apart and the cell lyses.
This is a consequence of the exceptionally high content of the acidic (negatively
charged) amino acids aspartate and glutamate in the glycoprotein of the
Halobacterium cell wall.
The negative charge on the carboxyl group of these amino acids is bound to
Na+; when Na+ is diluted away, the negatively charged parts of
the proteins tend to repel each other, leading to cell lysis.
Halophilic Cytoplasmic Components
Like cell wall proteins, cytoplasmic proteins of Halobacterium are highly
acidic, but it is K+, not Na+, that is required for activity.
High acidic amino acid composition
halobacterial cytoplasmic proteins typically contain lower levels of
hydrophobic amino acids and lysine

19. The ribosomes of Halobacterium also require high KCl levels for
stability, whereas ribosomes of nonhalophiles have no KCl
requirement.
Cellular components exposed to the external environment require high Na+
for stability, whereas internal components require high K+. With the
exception of a few extremely halophilic members of the Bacteria that also use
KCl as a compatible solute, in no other group of bacteria do we find this
unique requirement for such high amounts of specific cations.
Bacteriorhodopsin and Light-Mediated ATP Synthesis in Halobacteria
Certain species of haloarchaea can catalyze a light-driven synthesis of
ATP.
without chlorophyll pigments and it is not photosynthesis.
light-sensitive pigments are present including red and orange
carotenoids primarily C50
pigments called bacterioruberins and inducible pigments involved in
energy conservation

20. Under conditions of low aeration :
Halobacterium salinarum and some other haloarchaea
synthesize the
bacteriorhodopsin protein and
insert it into their cytoplasmic
membranes.
Conjugated to bacteriorhodopsin is
a molecule of retinal
carotenoid-like molecule that
can absorb light energy and
pump
a proton across the
cytoplasmic membrane.
Retinal :
The retinal gives
bacteriorhodopsin a purple hue.

21. Thus cells of Halobacterium that are switched from growth under high-
aeration conditions to oxygen-limiting growth conditions
(a trigger of bacteriorhodopsin synthesis)
gradually change color from orange-red to purple-red as they synthesize
bacteriorhodopsin and insert it into their cytoplasmic membranes.
Bacteriorhodopsin absorbs green light around 570 nm
The retinal of bacteriorhodopsin, which normally exists in a trans configuration
(RetT), becomes excited and converts to the cis (RetC) form.
Then
This transformation iscoupled to the translocation of a proton across the
cytoplasmic membrane.

22. The proton pump is then ready to repeat the cycle. As protons
accumulate on the outer surface of the membrane, a proton motive force
is generated that is coupled to ATP synthesis through the activity of a
proton-translocating ATPase.
Bacteriorhodopsin-mediated ATP production in H. salinarum
supports slow growth of this organism under anoxic conditions.
Antiport
The light-stimulated proton pump of H. salinarum also functions
to pump Na+ out of the cell by activity of a Na+__H+ antiport system
and also drives the uptake of nutrients, including the K+
needed for osmotic balance.
Symport
Amino acid uptake by H. salinarum is indirectly driven by light because
amino acids are cotransported into the cell with Na+ by an amino acid–Na+
symporter removal of Na+ from the cell occurs by way of the light-driven
Na+–H+ antiporter.

23. Thank you for your
attention