A Hot Affair

Hot water deep-sea clefts are a phenomenon that is very difficult to study. They were discovered in 1977 and today it is known that they occur in many places on the bottom of the sea. A cleft opens where the earth crust is unstable. As soon as cracks are formed, seawater seeps into depths, where hot rocks are and is expelled when the temperature inside the crack has brought it to a boil. In the vicinity of such clefts, the temperature may reach up to 420°C. Small particles and hot water, which is enriched with rock material, are catapulted out of the cleft and cause extreme poisoning of the surrounding water.

Life Under Hostile Conditions

Therefore, scientists all over the world were surprised to find out that these hot and toxic environments were swarming with – very unusual - life. Since 1977, 300 new species have been discovered in hydrothermal clefts. The eco-systems are based on bacteria, which utilise hydrogen sulphide and the heat of the crack to build complex food molecules. These bacteria serve as a source of food for all other creatures that live in these cracks. For some, the bacteria are the source of energy, but others use the bacteria in a different way. There are certain worms, which posses neither bowels nor a digestive system. They consist of living bacteria instead, which form their tissue (each gram of the worm is made of millions of bacteria) and provide everything the worms need. In exchange, the blood stream of the worm supplies the huge bacteria stock with hydrogen sulphide.

	The biggest bacterium of the world is as big as the head of a fruit fly. It is called Thiomargarita namibiensis.
Thiomargerita with drops of sulphur (light)

Thiomargarita belongs to the Beggiatoales. These giant bacteria live on the bottom of the sea in filaceous colonies and grow to a diameter of up to 0.75 mm. They are able to accumulate sulphide and nitrate. Most of the cell (98%) is filled by a liquid-filled vacuole, which contains nitrate in a 10 000 times higher concentration than the surrounding seawater. Nitrate is required to oxidise the sulphide. No other bacterium is able to do this anaerobically.

The smallest cells, by the way, are bacteria as well: Mycoplasms (approx. 50 nm).