| This bacterium was discovered in 1997 by Heide Schulz of the Max Planck Institute, in sediment off the coast of Namibia. It is generally between .1 and .8 millimeters in diameter, and is an opalescent white in color due to the sulfur reserve granules stored on its cellular periphery. In Latin, the organism is called Thiomargarita namibiensis, which is translated literally as this node's title, for easier reference.
If you're paying attention, you may have noticed in the last paragraph that the figure given for the organism's diameter was a few orders of magnitude larger than most prokaryotes. Its size is what allows it to be seen as being white with slight magnification and reflected light, as opposed to other bacteria which must be stained and viewed with a microscope. In fact, the recently newly discovered organism is the largest bacterium known to science, and is one-hundred times larger than its nearest competitor. As a point of interest, the Sulfur Pearl is not the largest monocellular organism overall, a title which belongs to the siphonous green algae.
The environment where this bacterium grows is not exactly conducive to life, at least by most organisms' standards. For one, the oxygen levels in the coastal area and depth at which the Sulfur Pearl lives are near zero, and accordingly its metabolism is anaerobic. Also, the sediment is actually toxic to even other anaerobic bacteria because of its high concentrations of hydrogen sulfide.
Curiously, it is actually this chemical that allows the Sulfur Pearl to survive, by being utilized for energy by its unique metabolism. Hydrogen sulfide can oxidize with nitrite, a reaction which produces energy for the organism and gives off a byproduct of oxygen. Unfortunately, seawater levels of nitrite are not always high enough for this reaction to take place easily, and can be low for months at a time between storms that bring fresh water. Put that all together, and you find the reason for the bacterium's size -- it has a central aqueous vacuole which makes up 98% of its volume, and stores enough nitrite to survive for two or three months. Taking the aforementioned sulfur storage on its surface into account, you end up with a creature hardy enough to survive such harsh conditions.
Because of its oxygen output and nitrate processing abilities, this prokaryote is an important player in the coastal ecosystem it inhabits, which makes it even more curious that it wasn't discovered earlier. These properties have also put it into consideration for introduction to coastal waters polluted by excess nitrates from fertilizer and other agricultural runoff. This sounds like a terrifically bad idea to me (see also: Caulerpa taxifolia), but what do I know.... | 
