The environments of Earth include conditions in which physical and chemical extremes make it very difficult for organisms to survive. Conditions that can destroy living cells and biomolecules include high and low temperatures; low amounts of oxygen and water; and high levels of salinity, acidity, alkalinity, and radiation. Examples of extreme environments on Earth are hot geysers and oceanic thermal vents, Antarctic sea ice, and oxygen-depleted rivers and lakes. Organisms that have evolved special adaptations that permit them to live in extreme conditions are called "extremophiles."
Photo by: Dmitry Pichugin
"Thermophiles" are microorganisms with optimal growth temperatures between 60 and 108 degrees Celsius, isolated from a number of marine and terrestrial geothermally-heated habitats including shallow terrestrial hot springs, hydrothermal vent systems, sediment from volcanic islands, and deep sea hydrothermal vents. -Encyclopedia of Environmental Microbiology, 2002. vol.3.
Temperature and bacteria
The lowest temperature at which a particular species will grow is the minimum growth temperature, while the maximum growth temperature is the highest temperature at which they will grow. The temperature at which their growth is optimal is called the optimum growth temperature. In general, the maximum and minimum growth temperatures of any particular type of bacteria are about 30°F (-1°C) apart. Most bacteria thrive at temperatures at or around that of the human body 98.6°F (37°C), and some, such as Escherichia coli, are normal parts of the human intestinal flora. These organisms are mesophiles (moderate-temperature-loving), with an optimum growth temperature between 77°F (25°C) and 104°F (40°C). Mesophiles have adapted to thrive in temperatures close to that of their host. Psychrophiles, which prefer cold temperatures, are divided into two groups. One group has an optimal growth temperature of about 59°F (15°C), but can grow at temperatures as low as 32°F (0°C). These organisms live in ocean depths or Arctic regions. Other psychrophiles that can also grow at 32°F (0°C) have an optimal growth temperature between 68°F (20°C) and 86°F (30°C). These organisms, sometimes called psychrotrophs, are often those associated with food spoilage under refrigeration. Thermophiles thrive in very hot environments, many having an optimum growth temperature between 122°F (50°C) and 140°F (60°C), similar to that of hot springs in Yellowstone National Park. Such organisms thrive in compost piles, where temperatures can rise as high as 140°F (60°C). Extreme thermophiles grow at temperatures above 195°F (91°C). Along the sides of hydrothermal vents on the ocean bottom 217 mi (350 km) north of the Galapagos Islands, for example, bacteria grow in temperatures that can reach 662°F (350°C). pH and bacteria
Like temperature, pH also plays a role in determining the ability of bacteria to grow or thrive in particular environments. Most commonly, bacteria grow optimally within a narrow range of pH between 6.7 and 7.5. Acidophiles, however, prefer acidic conditions. For example, Thiobacillus ferrooxidans, which occurs in drainage water from coal mines, can survive at pH 1. Other bacteria, such as Vibrio cholera, the cause of cholera, can thrive at a pH as high as 9.0. Osmotic pressure and bacteria
Osmotic pressure is another limiting factor in the growth of bacteria. Bacteria are about 80-90% water; they require moisture to grow because they obtain most of their nutrients from their aqueous environment. Examples of Extreme Communities
The deep sea environment has high pressure and cold temperatures (1 to 2 degrees Celsius [33.8 to 35.6 degrees Fahrenheit]), except in the vicinity of hydrothermal vents, which are a part of the sea floor that is spreading, creating cracks in the earth's crust that release heat and chemicals into the deep sea environment and create underwater geysers. In these vents, the temperature may...
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