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In hostile environments such as hot springs, volcanic craters and deep-sea hydrothermal vents – uninhabitable for most life forms – microscopic organisms are in full swing. How? Everything is in the way they wrap themselves.
Researchers at Stanford University have identified a protein that helps these organisms form a lipid-protective protective cell membrane – a key to resisting extremely acidic habitats.
Scientists knew that this group of microbes – called archaea – was surrounded by a membrane composed of chemical components different from those of bacteria, plants or animals. They had long speculated that perhaps this was what offered protection in extreme habitats. The team directly demonstrated this idea by identifying the protein that creates the unusual membrane structure in the species Sulfolobus acidocaldarius.
The membrane structures of some organisms are conserved in the fossil record and can serve as molecular fossils or biomarkers, leaving traces of what was living in the environment a long time ago. The search for preserved membrane lipids, for example, could indicate when an organism has evolved and how that might have been the circumstance of its environment. Being able to show how this protective membrane is created could help researchers understand other molecular fossils in the future, offering new evidence of the evolution of life on Earth. The results are published the week of December 3 in the Proceedings of the National Academy of Sciences.
"Our model is that this organism has developed the ability to make these membranes because it lives in an environment where acidity changes," said co-author Paula Welander, assistant professor of Earth System Science at Stanford School. of Earth, Energy & Environmental Sciences. (Stanford Land). "This is the first time we have been linking part of a lipid to an environmental condition in the archaea."
Rare chemistry
Hot springs in which S. acidocaldarius occurs, such as those in Yellowstone National Park where temperatures are above 200 degrees Fahrenheit, may experience fluctuating acidity. This organism is also present in volcanic craters, deep-sea hydrothermal vents and other acid environments at moderate and cold temperatures.
Welander is interested in studying this microbe because of its rare chemistry, especially its unusual lipid membranes. Unlike plants and fungi, Archean organisms do not produce protective cellulose walls and their membranes do not contain the same chemicals as bacteria. Scientists have explored how the species produced its unusual membrane for about 10 years before the end of experiments in 2006, she said.
"I think we forget that some things are not over yet, and I've seen it since I entered the world of geobiology," Welander said. "There are so many questions that we need only basic knowledge, such as," What is the protein that does this? Does this membrane structure really do what we say? "
Welander and his team already knew that the organisms produced a membrane containing a ringed molecule called calditol. The group thought that this molecule might underlie the ability of the species to withstand environments where other organisms perish.
To find out, they first analyzed the genome of S. acidocaldarius and identified three genes likely to be involved in the manufacture of a calditol. They then mutated these genes one by one, eliminating the proteins that these genes created. The experiments revealed a gene that, once mutated, produced S. acidocaldarius lacking calditol in the membrane. This mutated organism was able to grow at high temperatures but withered in a highly acidic environment, suggesting that protein is needed both to make the unusual membrane and to resist acidity.
The work was particularly difficult because Welander's laboratory had to reproduce these acid and high temperature conditions in which the microbes develop. Most of the incubators in his laboratory only reach body temperature, lead author Zhirui Zeng, a postdoctoral researcher at Welander's lab, discovered how to emulate the body's house with a small special oven. she explained.
"It was really cool," said Welander. "We have a lot of experience trying to understand chemistry."
Third area of life
Graphic illustrating three areas of life. This work goes beyond the discovery of a single protein, Welander said. His research focuses on lipids in current microbes to understand the Earth's history, including ancient climatic phenomena, massive extinctions, and evolutionary transitions. But before scientists can interpret evolutionary characteristics, they must understand the basics, such as the creation of new lipids.
Archaea are sometimes called the "third area of life", one being bacteria and the other, plants and animals, known as eukaryotes. Archaea includes some of the oldest and most abundant forms of life on the planet, without which the ecosystem could not collapse. Archaea are particularly abnormal microbes, confused with bacteria one day and assimilated to plants or animals the next day because of their unique molecular structures.
The research is particularly interesting because the classification of archaea is still debated by taxonomists. They have been separated from the domains of bacteria and eukaryotes in the last two decades as a result of the development of genetic sequencing in the 1970s.
"There are some things about archaea that are different, like lipids," Welander said. "Archaea are an important area of research right now because they are this different area that we want to study and understand – and they are really great."
This article has been republished from documents provided by the School of Earth Sciences, Energy and Environment Stanford. Note: Content may have changed for length and content. For more information, please contact the cited source.
Reference
The membrane lipids bound to Calditol are necessary for acid tolerance in Sulfolobus acidocaldarius. Zhirui Zeng, Liu Xiao-Lei, Jeremy H. Wei, Roger E. Summons and Paula V. Welander. PNAS published before printing on December 5, 2018 https://doi.org/10.1073/pnas.1814048115.
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