This article is edited from material prepared for an exhibit at the California Academy of Sciences called “Extreme Life”.
Deep–Sea Hydrothermal Vents
Discovered in 1977, hydrothermal vents, also known as "black smokers", revolutionized our understanding of life. Until the discovery of these vent systems, all known ecosystems on Earth had photosynthetic organisms at the base of their food chain. This vent ecosystem, however, is dependent on chemosynthetic bacteria that generate energy from hydrogen sulfide, the chemical responsible for the smell of rotten eggs.
The chemotrophic (chemical eating) bacteria exist in symbiotic relationships with other members of the ecosystem, including mussels and 8-foot long tubeworms. These tubeworms have no mouth, gut or anus. Instead, they have a giant organ in the center of their body called a "trophosome." It is filled with symbiotic bacteria that take on all the digestive and excretory functions of the worms.
Pompeii worms, like the one pictured below, are also found close to these vents. These worms are the most heat-tolerant among the complex life forms on Earth. They are able to thrive in 176°F water, whereas the Sahara Desert ant, the next most heat-tolerant complex organism, can only survive in temperatures up to 136°F.
The bluish "hair" covering Pompeii worms is actually made up of bacteria that produce heat-resistant enzymes. Researchers believe these enzymes could have a variety of applications, including pharmaceutical production and food processing. In addition to supporting a variety of worms, hydrothermal vents also support organisms such as crabs, shrimp and fish.
Methane seep ecosystems on the ocean floor are based on methane hydrate, a crystallized form of methane. Although it looks remarkably similar to ice, if you hold a match to methane hydrate, it will burn—thus its nickname "fire ice". It has a much higher melting point than water and it is a poor conductor of heat. Even though it is frozen, it doesn't feel cold when you touch it.
In 1997, ice worms (see below) were discovered living on the surface of methane hydrate, and their principle source of food was methane-eating bacteria. Other organisms have also been found subsisting on the methane, including mussels, clams and 100-year-old tubeworms. The mussels and clams have developed a symbiotic relationship with methane-eating bacteria. Without these bacteria to turn the methane hydrate into usable energy for them, the mussels and clams would not survive.
Ocean Floor Brine Pools
Underground salt deposits fill depressions in the ocean floor. These deep ocean brine pools are five times saltier than the surrounding ocean water and can kill creatures that accidentally swim into them.
Not only do these pools have highly concentrated salt solutions, they also have methane. This methane supports methane-eating bacteria, which work in a symbiotic relationship (in this case, mutually beneficial, or mutualism) with mussels that gather on the "shores" of these pools.
In the photo below, a submarine floats above a brine pool. Mussels line the dark brine pool to the left.
And as seen in the photo below, tube worms and pink polychaete worms also line the brine pool's edge, and they in turn lure other organisms such as eels and fish. These pools are oases of life on the otherwise less-populated ocean floor.
Hot springs are often surrounded by a wide variety of rocks that influence the water chemistry. Because of this, they can support large numbers of poly-extremophiles. These organisms are adapted to living under multiple combinations of hostile conditions, including hot and acidic, hot and sulfidic, hot and alkaline, or hot and filled with toxic heavy metals.
Yellowstone's Grand Prismatic Basin is a beautiful example of a hot spring. It is 300 feet across and its blue center is the product of uncommonly pure water bubbling up into the pool's center. All of the other colors are the product of photosynthetic, thermophilic (heat loving) bacteria flourishing in the boiling water. These bacteria survive temperatures ranging from 147°F (64°C) to 225°F (107°C).
To provide a sense of scale, the grey line on the left hand side of the picture above is a walkway, with the people appearing on the path as tiny dots that are barely visible.
Vast bacterial mats are found in regions around hot springs such as the Grand Prismatic Springs. There are more bacteria alive in 6 square centimeters (about 1 square inch) of this bacterial mat than there are humans in existence.
Microbes at the top of the mat use sunlight to produce chemical byproducts. Microbes below the upper layer use these chemicals for energy, then recycle nutrients back to the top.
The thin pink strands in the picture above are linked, chain-like colonies of chemotrophic bacteria that derive their energy from the chemicals they eat. These bacteria feed on sulfides in the hot spring water in much the same way as the bacteria that thrive near deep–sea hydrothermal vents.
Sub Sea Floor
In 1991, the species of Arcobacter shown below was discovered in the underwater dust plume that resulted from a volcanic explosion on the Earth's floor. These strange bacteria, which live in warm sediments well below the ocean floor, were stirred up by the huge volcanic explosion. They use the energy of the Earth’s core to flourish and are probably very similar to the first life forms that evolved on this planet.
Bacteria are happy to exploit the crooks and crevasses of rocks. However, some bacteria don't just live inside these cracks, they live inside the actual rocks. They exist as the only organisms on the planet that are completely independent of any oxygen produced by photosynthesis.
Basalt eaters, like those pictured above, are evidenced by the tunnels they create in rock. Although they exist independently of oxygen produced by photosynthesis, they do use oxidation as their source of energy -- performing any needed oxidation from the rocks themselves.
Lakes Mono Lake is three times saltier than the ocean. Because of the high density of Mono Lake's briny water, swimmers can float in it with little or no effort. It is also highly alkaline, with a pH of 10. This is comparable in strength to a strong detergent. The bacteria that thrive in this environment are poly-extremophiles, because they overcome at least two factors that can be barriers to life at extreme levels, salinity and pH.
The strange structures pictured above, called "tufa," were only revealed a few decades ago when tributaries to Mono Lake were diverted to supply water to Los Angeles, and the water level in Mono Lake dropped. These delicate structures were formed by the interaction of underwater springs with calcium carbonate (the main component of seashells). They are now eroding away because of exposure to the elements.
Snottites win the prize for the microbe with the coolest name. These colonies of single-celled bacteria hang from the walls and ceilings of caves. They are similar to small stalactites, but have the consistency of "snot," or mucus. sulfur-rich water that seeps into caves, and they live ensconced in a biofilm (a layer of viscous liquid or gel produced through biological activity) that protects them from the sulfuric acid in their environment. This acid is as strong as the acid found in car batteries!