When life gave them lemons, they made “extremo-nade”. In the 1970’s, scientists found microorganisms in extreme environments that could digest chemicals from the Earth itself. These microorganisms became known as extremophiles. Extremophiles are microorganisms – whether they are viruses, prokaryotes, or eukaryotes – that thrives under extreme environmental conditions. “Extremophile” is a combination of the suffix phile, meaning “lover of” and a prefix specific to their environment (Extreme environments, 2016). A few examples of the extreme environments these microbes find themselves in include intense heat (thermophile), extreme cold (psychrophile), salinity (halophiles) and high levels of radiation (radioresistant microbes), to name a few. Extremophiles are thought to be some of the earliest life forms on Earth, since such organisms most likely adapted to survive such harsh conditions. Many extremophiles are simple, single-celled life forms, and yet many are not. Extremophiles occur in all three domains of life: Bacteria, Archaea, and Eukarya.
The first extremophile, a thermophile, was found in the late 1960’s. This thermophile, now known as Thermus aquaticus, was found in the hot springs of the Yellowstone National Park in Wyoming, and is capable of growth at temperatures exceeding 70˚C.
Following are some categories into which the extremophiles found on Earth can be divided into:
Psychrophiles are organisms with the ability to survive in extremely cold conditions. They are commonly found in deep ocean water which has a fairly constant temperature of 2˚C, but because of the salt content, in colder areas, ocean water can reach temperatures of -12˚C without freezing. Psychrophiles use a variety of metabolic pathways, including photosynthesis, chemoautotrophy (also sometimes known as lithotrophy), and heterotrophy. They form robust, diverse communities. Their enzymes are structurally unstable and cannot operate at room (or ambient) temperature. The membranes of psychrophilic bacteria are more pliable at colder temperatures, making chemical reactions possible that otherwise would not occur if the membrane was semi-frozen. Some psychrophiles have developed substances, such as glycerol or antifreeze proteins which lowers the freezing point of water by several degrees. Others form symbiotic relationships with other organisms. Lichens are composite organisms that form when fungi form symbiotic partnerships with a photosynthetic partner- either an algae or a cyanobacteria. These lichens live on many rock surfaces in Antarctica. These partnerships allows each species to survive and thrive in these environments. An example of a psychrophile is chryseobacterium greenlandensis which for the last 120, 000 has survived nearly two miles deep within the ice of a Greenland glacier.
Thermophiles reproduce, and grow readily in temperatures above 45˚C, and some of them, referred to as hyperthermophiles favor temperatures above 80˚C. Some hyperthermophiles thrive in temperatures hotter than 100˚C. Thermophiles have various adaptations that allows them to tolerate a broad range of temperatures. Their proteins and nucleic acids are structurally modified to confer greater heat stability so that the cellular machinery is able to function. Thermophiles can be found in hot springs, volcanoes, hydrothermal vents and so forth. Hydrothermal vents, sometimes called smokers, are natural undersea chimneys through which superheated mineral-rich fluid as hot as 350˚C erupts. The most heat-resistant hyperthermophile Pyrolobus fumarii, grows in the walls of hydrothermal vents (http://atropos.as.arizona.edu/aiz/teaching/a204/extremophile.pdf, 2016). It reproduces optimally in an environment with a temperature of about 105˚C and can multiply in temperatures of up to 113˚C. It ceases to grow at temperatures below 90˚C, as it is too cold. Most thermophiles follow a simple diet, living only off the metals, gases, and minerals found in hydrothermal vent fluid. Some thermophiles only require sulfur, hydrogen and carbon dioxide (Divediscover.whoi.edu, 2016).
Organisms that can consistently survive doses of radiation 500 times greater than the lethal dose for humans. They often use the energy from radioactivity to produce food. Some radioresistant microbes evolved DNA repair mechanisms that reverses any genetic damage caused by radiation. One example of a radioresistant microbe is the Deinococcus radiodurans bacterium, which holds the Guinness Book record for being “the world’s toughest bacterium”. It has also been nicknamed “Conan the Bacterium” (HUYGHE, 1998), as a tribute to its toughness.
They are organisms that can survive in very salty environments. They are found in environments with a salt concentration 3 – 5 times higher than that of the ocean, such as the Dead Sea and evaporation ponds. Halophiles are coated with a special protein layer that blocks excessive salt from entering its cells. They prevent dehydration by increasing the internal osmolarity of the cell by accumulating organic compounds– osmoprotectants (protects the organism from osmotic stress e.g. sugars) –in their cytoplasm. Dunaliella salina is a halophilic algae lives in salt ponds and concentrates beta-carotene in its cell walls, resulting in an orange or pinkish colour.
Alkaliphiles have the ability to survive in alkaline environments (pH values from 8 – 11). They have unique enzymes, specialized cytoplasm and efficient cell membranes to protect their cells from damage. These microbes, in order to survive, maintain a relatively low alkaline level of 8 pH inside their cells by constantly pumping hydrogen ions (H+) in in the form of hydronium ions (H3O+) across their cell membranes and into their cytoplasm (Boundless.com, 2016). Alkaphiles can be further categorized at obligate alkaphiles (they require a high pH to survive), facultative alkaliphiles (they can survive under high pH conditions, but also grow under normal conditions) and haloalkaliphiles (they require high salt contents to survive). Alkaliphiles have the ability to change the pH of their environment to suit their growth. The colonies of the Microcystis bacterium flourishes in the extremely alkaline Mono Lake in California.
Acidophiles survive in extremely acidic environments, usually at pH 2 or below. Ferroplasma acicdiphilum (found in mine drainage, waste treatment plants and acidic caves) extracts energy from iron, “eating” the metal and leaving rust behind. Acidophiles have adapted a variety of mechanisms to maintain a neutral internal pH through passive and active regulation. Passive regulation does not expand energy and focuses on enforcing the cell membrane against the unfavorable environment. Passive regulation also includes biofilm secretion, incorporation of protective molecules into the cell membrane or the production of buffer molecules to raise the pH of the organism’s environment. Some acidophiles evolved active pH regulation methods that require energy and give the cell the ability to pump hydrogen ions out of the cell. This Extremophiles are very useful in the microbiology and biotechnology industry. They have unique enzymes, called “extremozymes” that enable them to function in harsh environments.Taq polymerase, isolated from Thermus aquaticus, is used in the polymerase chain reaction (PCR), due to their high thermostability. Polymerase chain reaction, or PCR, is a technique used in the laboratory to make multiple copies of a segment of DNA. It is very precise and can be used to amplify, or copy, a specific DNA target from a mixture of DNA molecules. Psychrophiles are used in the detergent industry, food industry and special applications like contact lens cleaning (http://biomikro.vscht.cz/vyuka/psychro/Prague_Biotech_Extremo.pdf, 2016). Deinococcus radiodurans (radioresistant microbe) can be used to clean up radioactive waste, solvents and heavy metals that contaminate soils.Extremophiles can thrive in conditions that would terminate humans in seconds. Extremophiles can survive in environments where no other life forms can, they are the Chuck Norris of organisms maintains the internal pH at around 6.7-7.0 (Everyday Life – Global Post, 2016).
2023 Update
Since this essay was written in 2016, there have been several significant discoveries and advancements in the field of extremophiles. Here are a few updates that could be added to bring the essay up-to-date:
- New extremophile species discovered: Several new extremophile species have been discovered since 2016, including a bacterium found in the Mariana Trench that can break down plastic and a bacterium found in a hot spring in Yellowstone National Park that can survive in extreme temperatures and high levels of acidity.
- Applications in biotechnology: Extremophiles are increasingly being used in biotechnology, particularly in the production of enzymes and other biomolecules that have industrial and medical applications. For example, enzymes from extremophiles have been used to develop detergents that work at low temperatures, reducing energy consumption.
- Origins of life: The study of extremophiles has provided insights into the origins of life on Earth and the possibility of life on other planets. For example, the discovery of extremophiles in extreme environments such as hydrothermal vents has led to the hypothesis that life on Earth may have originated in similar environments.
- Climate change: There is growing interest in the role of extremophiles in climate change, particularly in relation to the carbon cycle. Some extremophiles, such as methanogenic archaea, produce methane, a potent greenhouse gas. Understanding the role of extremophiles in the carbon cycle could help inform efforts to mitigate climate change.
- Space exploration: Extremophiles are also being studied in the context of space exploration, as they may provide insights into the possibility of life on other planets. For example, extremophiles found in ice on Earth are being studied as potential analogs for life on icy moons such as Europa and Enceladus.
- Ethics and conservation: The study of extremophiles raises ethical and conservation concerns, particularly in relation to the impact of human activities on extreme environments. Some extremophile species are endangered due to pollution and habitat destruction, highlighting the need for conservation efforts. Additionally, the commercialization of extremophile-derived products raises questions about the ownership and sharing of genetic resources.