Thiomargarita namibiensis: Giant Microbe

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Thiomargarita namibiensis Giant Microbe

• Thomas Aukland
• 5-29-03

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Distance Tree

• Determined by FISH 16S rRNA sequencing
• Identified as a gamma proteobacterium

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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--gtwait for the nutrients to come

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Size Comparison
.1-.75 mm in size Largest bacterium 100-200 times
larger than average bacterium
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Community characteristics

• Grow in long, loosely connected strands,
  reminiscent of a strand of pearls.
• Held in line by a common mucous sheath

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Location

• Fluid sediments and turbulent waters off Namibia
• Strong ocean currents ll to a N-S continental
  shelf
• E motion of the turning Earth --gtcurrents 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

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OVERHEAD PICTURE
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FOOD SOURCE
Diffusion of H2S and nitrate and
Oxygen nitrate-respiring sulfide-oxidizers?chemoli
thotroph
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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.

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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

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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

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Experiment ContAddition 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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ExperimentO2 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

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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

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Experiment Implications

• T. namibiensis may take up O2 in the
  presence/absence of nitrate.
• O2e- acceptor
• Anoxic times nitrate is acceptor
• Used to survive hard times

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References

• Schulz, H.N. Bo Barker Jørgensen BIG BACTERIA 
• Annu. Rev. Micrbiol. 2001, Vol. 55 105-137.
• 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.
• 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
  284493-495.
• http//www.accessexcellence.org/WN/SUA12/marg499.h
  tml
• http//www.scienceagogo.com/news/19990318191806dat
  a_trunc_sys.shtml
• http//www.sciencenews.org/sn_arc99/4_17_99/fob5.h
  tm
• http//www.cnn.com/NATURE/9904/15/biggest.bacteria
  /
• http//www.eurekalert.org/pub_releases/1999-04/AAf
  t-BBEF-160499.php
• http//daac.gsfc.nasa.gov/CAMPAIGN_DOCS/OCDST/sulf
  ur_plume.html
• http//www.mpg.de/news99/news17_99.htm
• http//www.whoi.edu/media/news_giant.bacterium.htm
  l