Thiomargarita namibiensis is the largest bacterium ever discovered, with a diameter of around 0.3 mm, making it easily visible to the naked eye. It was found by Heide N. Shulz and others in 1999, on the continental shelf off of Namibia. There are no other species in the genus.
By studying Thiomargaritanamibiensis' genes, scientists were able to pinpoint the bacterium's placement in the phylogenetic tree, as close relations to the bacterial genera Triploca and Beggiatoa, which have to contend with similar environmental challenges.
Thiomargaritanamibiensis' environment poses the necessity for a unique adaptation: they have to be able to oxidize nitrate into sulfide in the low-nitrate conditions of their oxygen-poor habitat.
Thiomargaritanamibiensis is found in the sulfur-rich sediments of the ocean floor, where they play an important ecological role.
Thiomargaritanamibiensis has its ecological niche in the oxygen-poor but nutrient-rich sediment and can survive in this environment which is toxic for most animal life due to high levels of hydrogen sulfide.
They live in vertical sheaths in the sediment and shuttle up and down between the surface of the sediment, where they stretch up into the water to take up nitrate for respiration, and deeper parts of the sediment, where they find their energy source, sulfide, that can be stored effectively as sulfur.
Thiomargarita is a close relative of these bacteria, but unlike their smaller cousins they are unable to and do not need to move constantly up and down to get nitrate or sulfide.
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