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Almost 20 years ago, Tom Hanson of the University of Delaware started studying the bacteria Chlorobaculum tepidum (Cba. tépidum), an organism that lives only in volcanic hot springs, to understand how it captures the energy of light and chemicals to grow in that environment. Among the reasons to study the body, Cba. tépidum is one of the microbes that reoxidize sulfide, a compound that is toxic to humans. Because of Cba. tépidum and his relatives, we can live near parts of the earth where sulphide is produced by other forms of life, such as the ocean.
Now, in an article published in mbio, the American Society for Microbiology's open access journal, Hanson and his colleagues have unearthed a model never before seen in life, all trying to understand how a microbe from a hot spring makes a living.
Sulfide as Snickers
Hanson, a microbiologist at the School of Marine Science and Policy at the College of Earth, Ocean and Environment at the University of North Dakota, said it was important to understand microbes because without them, human life does not exist. Would not exist.
"Half of the oxygen we breathe is produced by the microbes of the ocean," Hanson said. "And if we did not have microbes destroying organic matter, we would have an accumulation of dead plant matter on lands that are hundreds of meters high, and these organisms continue to spin the carbon cycle. Rotate the oxygen cycle – in our case, they keep the cycle of sulfur turning. "
Hanson is particularly interested in microbes involved in work on sulfur. He explains that in the same way that humans breathe oxygen and produce harmless water, some organisms breathe sulfur and produce sulphide, which is toxic.
If there were no organisms that reoxidized this sulphide, humans could not live near the oceans. Fortunately for us, organizations like Cba. tépidum find some delicious hydrogen sulphide.
"We think of hydrogen sulphide as a rotten egg, and they think Snickers is banned," said Hanson.
Parents of Cba. tépidum are present in waters as close to Delaware as the Chesapeake Bay. Fortunately for life in the bay, they are there to consume their Snickers sulphide bars, keeping a cork on the sulphide coming out of the anoxic waters of Chesapeake Bay and helping to keep the upper waters of the bay oxygenated.
Thiols of low molecular weight
Cba. tépidum can not grow in the presence of oxygen, and Hanson said that he was interested in the bacteria because, if it acts as a plant, it requires light energy and the carbon dioxide to produce biomass, but in a very different way. A key difference is that even if the plants use water in this process and produce oxygen, Cba. tépidum uses hydrogen sulphide and manufactures sulphate. Hanson's lab has been working to try to find out exactly how Cba. tépidum converted hydrogen sulphide to sulphate.
Other microbiologists have speculated that the process of converting hydrogen sulphide to sulphate would involve an organic chemical compound called low molecular weight thiols, made by all of life. Thiols protect cells against oxidative stress and help them detoxify toxic chemicals in the environment.
Two surprising discoveries
Hanson and his team began investigating the thiols produced by Cba. tépidum and finally made two important discoveries in their search for possible mechanisms for hydrogen sulphide sulphate conversion.
First, they found a new thiol made by Cba. tépidum proves to be one of the most widespread among life on Earth. Second, they showed that, contrary to what they and other researchers thought, this thiol does not directly help Cba. tépidum metabolize hydrogen sulphide to sulphate, refuting the common assumption.
That's Jennifer Hiras, a former doctoral student at Hanson's lab at UD who is now working for Corning Inc., discovered a low molecular weight thiol that science had never seen before. Since it was a thiol novel, she and Hanson did not know exactly what they had found.
By breaking down the molecule and looking at the pieces in a mass spectrometer, they were able to say that the newly discovered thiol shared some parts with a thiol called bacillithiol (BSH), present in soil bacteria. Hanson said that these soil bacteria are also different from Cba. tépidum as humans are oaks. They could say that this new thiol had extra carbon and hydrogen atoms, but did not know exactly where they were on the molecule.
Fortunately for them, Chris Hamilton, a chemist at East Anglia University, had read Hiras' thesis and offered him his help in making versions of bacillithiol with additional carbon and carbon atoms. hydrogen.
"Chris worked on bacillithiol and could create candidate molecules in a test tube," Hanson said. "He proposed two potential candidates for what the new molecule could be.His laboratory made them, and one of them turned out to behave exactly like the molecule we find in Cba. tépidum. "
Because they knew the structure of this molecule made in the laboratory, the group was able to determine that Cba. tépidum Bacillithiol modifies by placing a methyl group on a nitrogen atom to form N-methyl-bacillithiol (N-Me-BSH), which is the name of the newly discovered compound.
Orphan enzymes
Once they discovered the structure of N-Me-BSH, they hypothesized that Cba. tépidum do this by first preparing bacillithiol and then using an enzyme called methyltransferase to add the methyl group. They could show that Cba. tépidum had genes allowing it to make bacillithiol using soil bacterial gene sequences to perform a search in Cba. tépidum genome.
This allowed them to search for genes in Cba. tépidum who code methyltransferases but where they did not know how these enzymes helped Cba. tépidum grow – which are known as orphan enzymes.
"Microbial genomes contain genes that encode many orphan enzymes," said Hanson. "One of my scientific goals is to donate houses to orphan enzymes, and I want to find out how these enzymes help microbes make a living in the world."
Using two candidate orphan methyltransferase candidates, Vidhya Raman, a postdoctoral fellow at Hanson's lab who now works at the Noble Research Institute, was able to produce strains of Cba. tépidum where the genes of these two methyltransferases were deleted. She discovered that an orphan strain no longer produced N-Me-BSH, but only BSH. It also deleted genes for bacillithiol synthesis and showed that these strains were no longer producing N-Me-BSH or BSH.
In analyzing these strains, the Hanson group has shown that the hypothesis that a low molecular weight thiol is used to transport sulfur atoms when sulfur metabolism is false. Instead, strains that could not produce the thiols were still able to completely metabolize the hydrogen sulphide to sulphate.
"Work in Cba. tépidum, an organism that lives only in volcanic hot springs, we have found this new molecule and can say exactly which genes are needed to allow the microbes to make it, "said Hanson.
With the help of this new information, they were able to use gene sequences to predict what different thiols are making. By collaborating with Javiera Norambuena, a PhD student from Rutgers University, they tested these predictions on other bacteria and showed that they were accurate.
Their work suggests that bacillithiol and related molecules such as N-Me-bacillithiol are much more common in all life forms, and appear to be the most common low molecular weight thiols in biology.
"Our human cells use a thiol called glutathione.glutathione has been the object of a lot of attention because it is found in humans and plants, but it turns out that our analysis indicates that glutathione is actually much less common than other thiols, "said Hanson. "This shows how biology and evolution can generate different pathways to the same goal: a thiol that protects cells from oxidative stress and toxic chemicals." In this case, the solution in humans and the plant is not the only nor even the most common. "
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