Thiomargarita namibiensis: Giant MicrobeThomas 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 SOURCEDiffusion of H2S and nitrate and Oxygen

nitrate-respiring sulfide-oxidizerschemolithotroph

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 gradientsfrom physiological activity– Exposed to 1 min of pure ethanol

• Cells killed no S inclusion lost

– Addition of methanolIm 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

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 nitrateno 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• 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 284:493-495.

• http://www.accessexcellence.org/WN/SUA12/marg499.html

• 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