In class, we often learn about the conditions necessary for life to exist – temperature, pressure, pH, and many other variables make an impact on the possibility of it. However, there exist certain cells that survive and even thrive in normally inhospitable environments, habitats with conditions that no complex organism would have a chance of enduring. These cells, called extremophiles, are found in many locations all over the world, and are being discovered even today due to the extreme nature of their habitats. Extremophiles are classified into different categories based on the type of extreme conditions they can survive in; below is information on some of the more interesting groups.
Anaerobe – An organism that can survive in an environment without oxygen. Spinoloricus cinzia is an anaerobe – it was discovered, along with two other anaerobic cells, in the sediment of a basin in the Mediterranean Sea. Electron microscope images reveal that the cell appears to lack mitochondria, possessing hydrogenosomes instead. The microbe is an obligate anaerobe, meaning that it cannot survive in aerobic conditions.
Hyperthermophile – An organism that can survive at extremely high temperatures (>60°C). Hyperthermophiles were first discovered in 1969 in the hot springs of Yellowstone National park; over 70 species of hyperthermophiles have now been discovered. The record temperature for survival and reproduction is 122°C (251.6°F) by Methanopyrus kandleri, found on the wall of a hydrothermal vent in the Gulf of California. Hyperthermophiles can survive at such high temperatures because their cell membranes have high levels of saturated fatty acids, allowing them to retain their shape at high temperatures.
Piezophile – An organism that thrives at high pressures. Piezophiles are most commonly found on ocean floors, where the pressure oftentimes exceeds 380 atm. One group of piezophiles are the xenophyophores, which have been found in the deepest ocean trench at 6.6 miles below the surface (Fun Fact: Xenophyophores are also the world’s largest unicellular organisms, with some species reaching 20 cm (7.87402 in) in diameter.
Radioresistant – An organism that is capable of living in an environment with high levels of ionizing radiation. The most radioresistant organism that has been discovered thus far is Thermococcus gammatolerans of the Archaea domain, which survives because it can rebuild its radiation-damaged chromosomes without a loss of their viability. This organism can survive 30,000 Gy of gamma radiation, whereas 4-10 Gy is a lethal dose for humans.
Polyextremophile – An organism that fits into more than one extremophile category; most extremophiles fit under this classification. An excellent example of a polyextremophile can be found in Lake Vostok, the largest of the subglacial Antarctic lakes located almost four kilometers under the ice. A Russian research team drilled out ice near the top of the lake in 2012 and discovered more than 3,500 species of microbes that had been living in the lake.
Microbes living in this environment can be classified as both piezophiles for thriving at a high pressure (created by the weight of the ice on the lake), and psychrophiles for being able to survive and reproduce at extremely low temperatures (Fun Fact: The temperature at the surface of the Lake Vostok drill was once recorded at -89.2°C (-128.56F), making it the coldest place on Earth).
(All images from Wikimedia Commons)