Thiomargarita namibiensis (the sulfur pearl of Namibia) is a Bactérie which was discovered in the sediments of the Namibian coasts , on the level of the continental Shelf. This bacterium is largest never discovered, it indeed has a diameter ranging between 100 and 300 µm, but certain cells can reach 750 µm and can be visible with the naked eye. This bacterium has the effect of surviving under conditions which can be hostile, at the same time rich in nutrient, low in oxygen and rich in sulfide. It presents moreover the characteristic to have at the same time a cycle of sulfur and a cycle of nitrogen at the time of sound Métabolisme.

It is a spherical bacterium, with positive coloring of Gram. Its Cytoplasme is tiny room to a narrow layer surrounding a central Vacuole containing nitrates necessary to oxidation of sulfides.

It is a bacterium chimiolithotrophe able to use nitrate like final acceptor of electrons in the respiratory Chaîne. The concentration nitrates some being fluctuating in its environment, the bacterium is able to store nitrate in its immense vacuole. When the nitrate concentration is weak in the environment, the bacterium uses nitrate contained in its vacuole for its breathing.

During anaerobic breathing, the bacterium oxidizes the Sulfure of hydrogen (H₂S) in element Soufre (S^o). Sulfur is deposited in the form of granules in the cytoplasm, thinking the light of the microscope, giving to the organization the aspect of a pearl.

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