This discovery is the result of close collaboration between several research groups at Max Planck Institute for Marine Microbiology. Cedric Hahn, Gunter Wegener and a team discovered that ethane-degrading microbes were present at the Guaymas Basin's hydrothermal vents. They are located at a depth of 2,000m in the Gulf of California. It was named Ethanoperedens thermophilum, which is a heat-loving ethane-eater. Cedric Hahn, a PhD student in the research group Molecular Ecology, cultured the ethane degrading microbes at the laboratory. These microorganisms were examined closely by Hahn, Wegener, and fellow researchers from the Microbial Metabolism research group, Tristan Wagner, and Olivier Lemaire. The secrets of ethane fixation were revealed by this collaborative effort. We were amazed at what we discovered. Gunter Wegener, scientist at the Research Group for Deep-Sea Ecology and Technology, says that there is a general similarity but some aspects of the enzyme are fundamentally different from their counterpart, the enzyme responsible for methane degradation.Ethane-eaters rely on the same enzyme that Methane-eatersGeothermal heat is responsible for the degrading of organic matter in deep-sea sediments to oil and natural gases like ethane. Different microorganisms consume the ethane. These include archaea which degrade the natural gas and bacteria which combine the electrons to reduce sulfate (a common compound in the ocean). Research has been reenergized by the discovery of ethane-eating microbes. The ethane specialists grow faster than microbes that eat methane, which takes a long time to grow. They also grow twice as fast every week. This reduces the time required to produce biomass, which allows for the purification and characterisation of key enzymes that catalyze the oxidation natural gas.Cedric Hahn used a molecular inhibitor to methane oxidation in his culture to test for similarities between the enzymes that catalyze the activation of methane and ethane. The treatment also stopped ethane oxygenation. Cedric Hahn says that this suggests that the ethane oxidizing archaea activates ethane in the same enzymatic reactions like those involved in methane generation/degradation. Tristan Wagner, who has been studying them for many years, is a specialist in these enzymes.Imagine a structure that is visualized with astonishing precisionOlivier Lemaire and Cedric Hahn, who were the first to publish the Science paper, tried to purify an enzyme that is responsible for ethane fixing. Olivier Lemaire says that the project was extremely challenging. "Usually, we extract the enzymes from much greater amounts of biomass in cultures containing only one microorganism. We were able to obtain sufficient quantities of enzymes to allow us to conduct structural analyses.Next, it was necessary to obtain crystals from the enzyme in order to determine its tri-dimensional structure. Tristan Wagner, head and expert in X-ray crystallography, says that X-ray crystallography has previously given excellent results for this group of enzymes. "We analyzed these crystals using X-ray diffraction, and solved the enzyme structure with unprecedented atomic resolution. This allows us to determine the positions of individual atoms, and thus obtain a very precise picture of the structure.This structure has many unique features. Olivier Lemaire says that the size of the catalytic chamber where the chemical reaction occurs is twice that in enzymes that capture methane. This makes sense, as ethane is larger than methane. Two additional methyl groups are contained in the cofactor, which is the catalyst for this reaction. Jrg Kahnt, an international expert on the cofactor, confirmed these methyl groups at the Max Planck Institute for Terrestrial Microbiology. Cedric Hahn says, "We discovered a protein that could cause these methylations and it is only present in ethane consumers." Because the chamber is larger, a regular cofactor would not work well and could cause the reaction to be impeded. The cofactor is held in place by the methylations.The tunnel connects the exterior and the catalytic chamber of the enzyme. The tunnel is not found in any other enzyme with similar properties. Researchers experimentally confirmed the existence of the tunnel in collaboration with Sylvain Engelberge, a scientist at the Paul Scherrer Institute (Switzerland), where protein crystals were gassed using xenon. Xenon was detected both in the catalytic chamber as well as the predicted tunnel, proving its existence. Modified amino acids and extensions have helped stabilize the tunnel.The spotlight now turns to butane and propaneThis enzyme structure shows how microbes from geothermally active sites became experts in ethane trapping. This research allows us to gain a better understanding of the first step of ethane degrading, which is the only energy source for these archaea. Tristan Wagner concludes that while it is important to understand the mechanism of ethane degradation, the discovery that an enzyme is capable of recognizing ethane over other alkanes was a significant step forward.How do we proceed with the research? Gunter Wegener says that previous research has shown that activation of longer alkanes is possible using similar enzymes. "We want to find out what the unique features of enzymes that activate propane and butane as a next step."
