(ORDO NEWS) — In 2016, during the expedition “370” in the Nankai Trench, microorganisms were discovered that can exist at a temperature of 120 degrees Celsius. A group of scientists from six countries studied these microorganisms and found that a high metabolic rate helps them withstand such extreme conditions. This is reported in an article published in the journal Nature Communications.
It is believed that sediments located below the level of the ocean floor (ultraabyssal) contain a large biological diversity of microorganisms. The existence of such organisms is limited by the availability of organic matter and the temperature, which rises by 30 degrees Celsius with every kilometer as it approaches the center of the Earth.
High temperatures damage proteins and nucleic acids that are essential for cell function. For a long time it was believed that 80 degrees Celsius is the highest temperature at which microorganisms can exist. But in 2016, Expedition 370, which included scientists from nine countries, explored the Nankai Trench, a deep-water trench in the Pacific Ocean located south of the Japanese island of Honshu.
During the expedition, the researchers extracted rock samples located at different depths. The deepest sample (1,177 meters below the ocean floor) was recovered from site C0023, where temperatures reached 120 degrees Celsius. Despite the abnormally high temperature, microorganisms were found in this sample. Due to the small number, it was not possible to establish the species composition of the population of microorganisms.
A team of scientists from Germany, Denmark, USA, Switzerland, Sweden and Japan, led by Tina Treude of the University of California at Los Angeles, examined microorganisms found in samples from the Nankai Trench, including a sample from site C0023.
Using radioisotope analysis of sulfur-35 and carbon-14, the researchers estimated the rate of sulfate reduction and methanogenesis characteristic of deep-sea microorganisms. Then the theoretical rate of biomass growth was calculated. The growth rate of the biomass of microorganisms extracted from site C0023 was several orders of magnitude higher than the metabolic rate of those that lived at shallower depths and at lower temperatures.
The authors note that the increase in the intensity of the metabolism of deep-sea microorganisms is most likely associated with an increase in energy costs for the elimination of thermal damage. First of all, such damages include racemization of amino acids – the spontaneous conversion of L-amino acids in the protein into D-amino acids.
Racemization can distort the structure of a protein and disrupt its function. Degrading such proteins and replacing them with new ones, including only L-amino acids, is the simplest and most energy-efficient way to solve this problem.
But this is possible only if there is a sufficient amount of amino acids in the external environment, and at temperatures above 45 degrees Celsius, they quickly decompose. Therefore, microorganisms are forced to use a more energy-intensive method and activate enzymes that convert D-amino acids into L.
Something interesting is often found in deep sea trenches. For example, in the Sunda Trench (Indian Ocean), at a record depth for cephalopods – over six thousand meters – an octopus from the genus Grimpoteuthis was discovered. And in the Atakama Trench (Pacific Ocean), at a depth of more than seven thousand meters, three new species of lipard fish were found.
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