Arsen(As)-Bakterium
Literature
A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus
(Wolfe-Simon et.al, 2010)
Absence of arsenate in DNA from arsenate-grown GFAJ-1 cells
(Redfield et.al, 2012)
Erwin Kralofsky
5. Dez 2012
Seminar
Astrobiology
1
Definition of Life
Life is mostly composed of the elements carbon, hydrogen,
nitrogen, oxygen, sulfur and phosphorus. Although these
six elements make up nucleic acids, proteins and lipids and
thus the bulk of living matter, it is theoretically possible that
some other elements in the periodic table could serve the same
functions. Here we describe a bacterium, strain GFAJ-1 of
the Halomonadaceae, isolated from Mono Lake, CA, which
substitutes arsenic for phosphorus to sustain its growth. Our data
show evidence for arsenate in macromolecules that normally
contain phosphate, most notably nucleic acids and proteins.
Exchange of one of the major bio-elements may have profound
evolutionary and geochemical significance.
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Bacteria-strain GFAJ-1
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Bacteria-Definition
Bacteria; (singular: bacterium) constitute a large domain of
prokaryotic microorganisms. Typically a few micrometers
in length, bacteria have a wide range of shapes, ranging
from spheres to rods and spirals. Bacteria were among the
first life forms to appear on Earth, and are present in most
habitats on the planet, growing in soil, acidic hot springs,
radioactive waste, water, and deep in the Earth´ crust, as
well as in organic matter and the live bodies of plants and
animals, providing outstanding examples of mutalism in
the digestive tracts of humans, termits and cockroaches.
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Bacteria-Definition
Prokaryotic ?
The prokaryotes are a group of organisms, whose cells lack a cell nucleus (karyon), or any
other membrane-bound organelles. The organisms whose cells do have a nucleus are called
eukaryotes.
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Bacteria - Definition
Organelle ?
In cell biology, an organelle is a specialized subunit within a cell that has a
specific function, and is usually separately enclosed within its own lipid
bilayer.
Lipid ?
Lipids constitute a broad group of naturally occurring molecules that include fats,
waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K),
monoglycerides, diglycerides, triglycerides, phospholipids, and others. The
main biological functions of lipids include energy storage, as structural
components of cell membranes, and as important signaling molecules.
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Mono Lake, CA
Small picture: 1969
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Phosphororus -> Arsenic
• Arsenic is a chemical analog of phosphorus (P) which lies
directly below P in the periodic table.
• Arsenic posesses a similar atomic radius, as well as near
identical electronegativity to P.
• Phosphate (PO43-) is the most common form of P in
biology.
• Arsenate (AsO43-) behaves similar to PO43- over a wide
range of chemical and biological properties.
• Both Phosphate and Arsenate are highly toxic. Metabolic
pathways cannot distinguish between the two molecules.
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Geomicrobiology of GFAJ-1
• GFAJ-1 grew at an average rate of µ=0.53 day -1
under +As/-P, increasing by over 20-fold in cell
numbers after 6 days.
• It also grew faster and more extensilvely with the
addition of 1.5 mM PO43- (-As/+P) µmax = 0.86 day
-1.
• However, when neither AsO43- nor PO43- was
added no growth was observed.
(see figure)
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Phosphor
Arsen
Nothing added
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Geomicrobiology of GFAJ-1
When grown under +As/-P conditions cells had 1.5 fold greater
intercellular volume. Transmission electron microscopy revelead
large vacuole-like regions in +As/-P grown cells that may
account in this increase of size.
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„controversal paper“
Absence of arsenate in DNA from arsenate-grown GFAJ-1 cells (Redfield
et.al, 2012)
We have found that arsenate is not needed for growth of GFAJ-1 when
phosphate is limiting. Additionally, we used mass spectrometry to show
that DNA purified from cells grown with limiting phosphate and
abundant arsenate does not contain detectable arsenate.
12
Growth curve from Redfield et.al,
2012
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Results from Redfield et.al, 2012
With 1500 µM phosphate but no added arsenate (WolfeSimon et al.’s -As/+P condition), this medium produced
~ 2 x 108 cells/ml, similar to the -As/+P yield obtained by
Wolfe-Simon et al. (1). The growth yield depended on the
level of phosphate supplementation, with even
unsupplemented medium giving significant growth (~ 5 x
106 cells/ml). This is four-fold lower than the ~2 x 107
cells /ml yield of Wolfe-Simon et al.’s +As/-P medium.
The growth analyses shown in this Figure were done in the
absence of arsenate, and thus demonstrate that GFAJ-1
does not require arsenate for growth in -P culture medium.
14
Condition used by Redfield et.al,
2012
-As: no arsenate;
+As: 40 mM arsenate;
-P: 3 µM phosphate,
+P: 1500 µM phosphate
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Results from Redfield et.al, 2012
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Results from Redfield et.al, 2012
deoxyadenosine-phosphate
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Results from Redfield et.al, 2012
deoxyadenosine-arsenate
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Conclusion
Wolfe-Simon (NASA Astrobiology Institute) found
a bacteria-strain (GFAJ-1) in the sediments in
Mono Lake, California and confirmed with several
measurements that it can grow using arsen (As) as
nutriment.
Redfield (University of British Columbia) analysed
the same strain and found that arsenate is not
needed for growth of GFAJ-1.
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Conclusion
Verification of results by independent
colleagues is essential in engineering and
science to confirm results.
The german sentence „Wer misst misst Mist“
seems to be right.
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Thank you for your attention.
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