Thiomargarita namibiensis: Giant Microbe

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

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 • 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

Thiomargarita namibiensis: Giant Microbe