Real survivors, in few words: Extremophiles

February 13, 2017

For sure, Dear Reader, you know Bear Grylls, one of the most known adventurers that have his own show about survival in extreme conditions. 40 degrees below zero on the Mt Everest, muddy Florida swamps full of mosquitoes or deep Amazon jungle... Do you really think that horrible place to live? Maybe for humans... and I think our hero should take a sit and learn for true professionals – Extremophiles.

Those “tough guys” are organisms that tolerate or require extreme environments to live and grow. The majority of extremophiles is unicellular life forms from an old domain called Archea, however, we can find a wide range of bacteria, multi-cellular forms like insects, fungi and plants. Researchers discovered them in many “hostile” conditions, whether in geysers, nuclear waste, deep-sea vents or in the Alaskan ice. In this article, few types of the extremophiles will be presented with few examples of Archea, bacteria and eventually known Eucariota.

From the beginning of our civilisation as scientists, we tried to classified and put all the life forms to “proper drawers”, to understand better the differences, connections and similarities of organisms around us. Basing on the environments colonised by extremophiles, we can distinguish many of groups (that classification is unnatural and contractual, however, help with summarising the knowledge and examples).

Temperature - limiting for most organisms: from five degrees to forty above zero, however life found a way to explore ice of lakes of Antarctica or geysers and thermal features around the world. Cryophiles (or Psychrophiles) prefer ice cold environments, they are present in Arctic and alpine soils, glaciers, snowfields and high-latitude and deep ocean waters. Most of them ranging -20 degrees to 15 Celsius degrees above zero. For examples, we can take the whole genus of Arthrobacter sp., Psychrobacter sp. and members of Sphingomonas, Pseudomonas or Hyphomonas.

In contrast, Thermophiles prefer temperatures above 41 degrees even up to 122 Celsius. We can distinguish two particular groups of thermophiles. First are the facultative thermophiles that can grow and survive in lower ranges of temperatures, below 50oC, while obligate thermophiles required for growth and survival really high temperatures even above 80oC. Examples are found in Archea: Pyrolobus fumarii, Methanococcus jannaschii or Aeropyrum pernix that can leave and grow in water above the boiling point, and bacteria Geothermobacterium ferrireducens, Aquifex aeolicus and Thermotoga maritima.

Another environmental condition that can be restrictive for many organisms is pH. There are two types of extremophiles on both ends of the pH range: Acidophiles with preferences to the environment below pH 3 and Alkaliphiles living in pH above 9. Acidophiles are found between Archea: Acidianus brierleyi, Acidianus infernus or Halarchaeum acidiphilum, bacteria from Acidobacterium genus or Acetobacter aceti, and also Eucariota like fungus Mucor racemosus or algae Dunaliella acidophila. Alkaliphile are bacteria: Natronomonas pharaonis and Thiohalospira alkaliphila.

There are organisms that are resistant to high temperatures and acidic environments below pH 3 found in sea vents or hot springs. They are called Thermoacidophiles and the most known are the red algae Cyanidiophyceae from hot springs in Yellowstone National Park, but in this group, we can find Archea, bacteria and other eucaryotic organisms.

For human beings and millions of higher organisms, the lack of oxygen itself is an extremal environmental condition. However, there are organisms that don’t need oxygen for energy production in the cells, even the presence of oxygen can be toxic for them. The organisms that not require oxygen for a living are called Anaerobes and there are two types of them, facultative anaerobes, that can survive with or without oxygen and also obligate anaerobes that are killed by the concentration of the atmospheric oxygen. To facultative anaerobes, we can count bacterial genus like Staphylococcus spp. or Streptococcus spp. or well know Escherichia coli. The obligate anaerobes are found in the genus of bacteria like Clostridium, Porphyromonas or Prevotella and fungi genus Neocallimastix and Sphaeromonas.

Another factor that can reduce life in the particular area is a high concentration of the substances like salts or metals. The beings preferring the higher concentrations of the salts (above 0.2M) are Halophiles. They are later divided into smaller groups depending on the tolerance of the salt concentrations, but here they will not be discussed. The represents for this types are found in several groups of living organisms from Archea, bacteria to algae and fungi. The extreme examples are bacterium Salinibacter ruber, Archea family Halobacteriaceae or algae Dunaliella salina. The presence of the heavy metals like iron, copper, arsenic, cadmium or zinc in the environment can be toxic for non-Metaltolerant organisms.

Water is named “source of life” and it is required for every living organism, but some of the organisms are able to survive on the border of dying off without the presence of water and they are called Xerophiles. The examples of xerophile are a fungus Trichosporonoides nigrescens or cacti like Pachycereus pringlei and Blossfeldia liliputana.

Last but not least, the ionizing radiation resistant organisms with the ability to sustain radiation above 1000 Gray, to give a scale human lethal dose is on the level from 4-10 Gy. The insects from the Braconidae genus and bacteria Deinococcus radiodurans or Thermococcus gammatolerans.

The extremophiles as a wide and differential group of organisms that live in the most hostile environments on Earth are the amazing examples of a variety of life and can lead humans to a better understanding of the not only life on our planet but also in the other universe!