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Thiomargarita namibiensis:
Giant Microbe
Thomas Aukland
5-29-03
Distance Tree
• Determined by FISH 16S rRNA sequencing
• Identified as a gamma proteobacterium
General Characteristics
• Store elemental sulfur just under the cell wall
• Nitrate in a huge vacuole
– 98% of total volume
• can live for up to 3 months
• Coupling the oxidation of sulfide with the
reduction of nitrate
– aerobic and anaerobic
• Not motile-->wait for the nutrients to come
Size Comparison
.1-.75 mm in size
Largest bacterium
100-200 times larger than average bacterium
Community characteristics
• Grow in long, loosely connected strands,
reminiscent of a strand of pearls.
• Held in line by a common mucous sheath
Location
• Fluid sediments and turbulent waters off Namibia
• Strong ocean currents: ll to a N-S continental shelf
• E motion of the turning Earth -->currents to the W
– Upwelling of deep ocean water that is unusually rich
with the nutrients
• Oxygen-poor but nutrient rich sediment
– water depth of about 300 feet
– top three centimeters of the sediment
OVERHEAD PICTURE
FOOD SOURCE
Diffusion of H2S and nitrate and Oxygen
nitrate-respiring sulfide-oxidizerschemolithotroph
Experiments: Schulz and DeBeer
• Purpose: investigation of how the cells survive
exposure to O2 or whether Thiomargarita cells can
use 02 as an e- acceptor in addition to nitrate for
oxidation of sulfide.
• Measurable gradients of 02 and H2S exist around
cells
• The physiological rxns of indiv. cells to changes in
O2 and H2S can be seen by measuring rates of
diffusion across cell membranes.
Experiment Setup
• Chain of T. namibiensis
in-with 250ml of art.
Seawater
– Clamped between 2 wires
• O2 controlled by
bubbling argon/air
• H2S added
• microelectrodes
– Gradient toward cells
– [O2] or H2S in medium
Experimental Fail Safes
• To prove: O2 and H2S gradientsfrom
physiological activity
– Exposed to 1 min of pure ethanol
• Cells killed no S inclusion lost
– Addition of methanolIm disappearance of
H2S and O2 gradients around cells
Experiment Cont:
Addition of Acetate
• Allowed the O2 gradients top remain stable
for about 2 days.
• Acetate may have been used as C s. and not
as a e- donor
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Experiment:O2 results
Presence of sulfide increased O2 uptake
Suggests the cells survive exposure to 02 and use it as an e- donor
Addition of nitrateno effect on O2 uptake
Observed sulfide flux under anoxic cond.
– Result from nitrate in vacuole
Experiment: H2S response under
aerobic conditions
• Decline in O2
– Increased uptake rates of sulfide
• Cells had a ceiling of 20uM of H2S fluxes
– Could tolerate levels-37uM
Experiment: Implications
• T. namibiensis may take up O2 in the
presence/absence of nitrate.
• O2:e- acceptor
• Anoxic times: nitrate is acceptor
– Used to survive hard times
References
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Schulz, H.N. & Bo Barker Jørgensen BIG BACTERIA
Annu. Rev. Micrbiol. 2001, Vol. 55: 105-137.
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Schulz, H. N., de Beer, D. (2002). Uptake Rates of Oxygen and Sulfide Measured with
Individual Thiomargarita namibiensis Cells by Using Microelectrodes. Appl. Environ.
Microbiol. 68: 5746-5749.
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Schulz, H. N., T. Brinkhoff, T. G. Ferdelman, M. Hernéndez Mariné, A. Teske, and B. B.
Jørgensen. 1999. Dense populations of a giant sulfur bacterium in Namibian shelf
sediments. Science 284:493-495.
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http://www.accessexcellence.org/WN/SUA12/marg499.html
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http://www.scienceagogo.com/news/19990318191806data_trunc_sys.shtml
http://www.sciencenews.org/sn_arc99/4_17_99/fob5.htm
http://www.cnn.com/NATURE/9904/15/biggest.bacteria/
http://www.eurekalert.org/pub_releases/1999-04/AAft-BBEF-160499.php
http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/OCDST/sulfur_plume.html
http://www.mpg.de/news99/news17_99.htm
http://www.whoi.edu/media/news_giant.bacterium.html