Mix and Match: How a Methanogen creates its own sulfate reduction machinery
Discovery opens up exciting opportunities in biofuel production
Tristan Wagner, Max-Planck-Institut für Marine Mikrobiologie
Marion Jespersen, Max-Planck-Institut für Marine Mikrobiologie
Sulfur, an essential building block of life
Sulfur is a fundamental element of life and all organisms need it to synthesize cellular materials. Autotrophs, such as plants and algae, acquire sulfur by converting sulfate into sulfide, which can be incorporated into biomass. However, this process requires a lot of energy and produces harmful intermediates and byproducts that need to be immediately transformed. As a result, it was previously believed that microbes known as methanogens, which are usually short on energy, would be unable to convert sulfate into sulfide. Therefore, it was assumed that these microbes, which produce half of the world's methane, rely on other forms of sulfur, such as sulfide.
A methanogen assimilating sulfate?
This dogma was broken in 1986 with the discovery of the methanogen Methanothermococcus thermolithotrophicus, growing on sulfate as the only sulfur source. How is this possible, considering the energetic costs and toxic intermediates? Why is it the only methanogen that seems to be capable of growing on this sulfur species? Does this organism use chemical tricks or a yet unknown strategy to allow sulfate assimilation? Marion Jespersen and Tristan Wagner at the Max Planck Institute for Marine Microbiology have now found answers to these questions and published them in the journal Nature Microbiology.
The first challenge the researchers met was to get the microbe to grow on the new sulfur source. “When I started my PhD, I really had to convince M. thermolithotrophicus to eat sulfate instead of sulfide,” says Marion Jespersen. “But after optimizing the medium, Methanothermococcus became a pro at growing on sulfate, with cell densities comparable to those when growing on sulfide.”
“Things got really exciting when we measured the disappearance of sulfate as the organism grew. This was when we could really prove that the methanogen converts this substrate.” This allowed the researchers to safely cultivate M. thermolithotrophicus in bioreactors in large scales, as they were no longer dependent on the toxic and explosive hydrogen sulfide gas for growth. “It provided us with enough biomass to study this fascinating organism,” explains Jespersen. Now the researchers were ready to dig into the details of the underlying processes.
The first molecular dissection of the sulfate assimilation pathway
To understand the molecular mechanisms of sulfate assimilation, the scientists analyzed the genome of M. thermolithotrophicus. They found five genes that had the potential to encode sulfate-reduction-associated enzymes. “We managed to characterize every one of those enzymes and therefore explored the complete pathway. A true tour de force when you think about its complexity,” says Tristan Wagner, head of the Max Planck Research Group Microbial Metabolism.
By characterizing the enzymes one-by-one, the scientists assembled the first sulfate assimilation pathway from a methanogen. While the first two enzymes of the pathway are well known and occur in many microbes and plants, the next enzymes were of a new kind. “We were stunned to see that it appears as if M. thermolithotrophicus has hijacked one enzyme from a dissimilatory sulfate-reducing organism and slightly modified it to serve its own needs,” says Jespersen. While some microbes assimilate sulfate as a cellular building block, others use it to obtain energy in a dissimilatory process – as humans do when respiring oxygen. The microbes that perform dissimilatory sulfate-reduction employ a different set of enzymes to do so. The methanogen studied here converted one of these dissimilatory enzymes into an assimilatory one. “A simple, yet highly effective strategy and most likely the reason why this methanogen is able to grow on sulfate. So far, this particular enzyme has only been found in M. thermolithotrophicus and no other methanogens,” Jespersen explains.
However, M. thermolithotrophicus also needs to cope with two poisons that are generated during the assimilation of sulfate. That´s what the last two enzymes of the pathway are made for: The first one, again similar to a dissimilatory enzyme, generates sulfide from sulfite. The second one is a new type of phosphatase with robust efficiency to hydrolyze the other poison, shortly known as PAP.
“It seems that M. thermolithotrophicus collected genetic information from its microbial environment that enabled it to grow on sulfate. By mixing and matching assimilatory and dissimilatory enzymes, it created its own functional sulfate reduction machinery,” says Wagner.
New avenues for biotechnological application
Hydrogenotrophic methanogens, such as M. thermolithotrophicus, have the amazing ability to convert dihydrogen (H2, for example artificially produced from renewable energy) and carbon dioxide (CO2) into methane (CH4). In other words, they can convert the greenhouse gas CO2 into the biofuel CH4, which can be used, for example, to heat our homes. To do this, methanogens are grown in large bioreactors. A current bottleneck in the cultivation of methanogens is their need for the highly hazardous and explosive hydrogen sulfide gas as a sulfur source. With the discovery of the sulfate-assimilation pathway in M. thermolithotrophicus, it is possible to genetically engineer methanogens that are already used in biotechnology to use this pathway instead – leading to safer and more cost-effective biogas production.
“An unresolved burning question is why M. thermolithotrophicus would assimilate sulfate in nature. For this, we will have to go out into the field and see if the enzymes required for this pathway are also expressed in the natural environment of the microbe”, concludes Wagner.
Other news from the department science
Start-up Colossal Biosciences Joins Biorescue In Its Mission To Save The Northern White Rhino From Extinction
Colossal will assist the rescue mission by leveraging genome sequencing and gene editing methods to save the endangered species
"For the first time, we have systematically measured the size and abundance of cells across all major tissues and organs"
What's that smell? New gut microbe produces smelly toxic gas but protects against pathogens
Taurine-degrading bacteria influence intestinal microbiome
Wastewater treatment plants as drivers for the energy transition
Technical add-on module can, in principle, turn any wastewater treatment plant into a CO2 sink and decentralized methane production plant
At which age we are at our happiest
An evaluation of over 400 samples shows how subjective well-being develops over the course of a lifespan
New approach to testing for long Covid
Blood vessels in the eye altered with persistent coronavirus symptoms
Researchers create pioneering approaches for the detection of viral antigens
Sybodies: a revolution in biological recognition
New SARS-CoV-2 variant Eris on the rise
SARS-CoV-2 lineage EG.5.1 has an advantage at evading neutralizing antibodies
Does the human brain have an Achilles heel that ultimately leads to Autism?
CHOOSEn fate: one brain organoid’s tale on Autism
Co-crystal improves the water-solubility of ASA
This could benefit patients diagnosed with suspected acute myocardial infarction
Observing nanoparticles with unprecedented precision
Illuminated: Researchers investigate new physical phenomena on the nanoscale with microstructured fibers
Falling Walls announces Science Breakthrough of the Year 2023 laureates
“These outstanding breakthroughs will change the face of the world and impressively prove what ingenuity, curiosity and courage can achieve”
Most read news
Cells with an ear for music release insulin
For the first time, researchers are using music, including Queen's global hit "We will rock you," to stimulate insulin release from cells
"Anti-obesity drugs" normalises brain in obesity
Anti-obesity drug improves associative learning in people with obesity
Microbe of the Year 2023: Bacillus subtilis – for health and technology
Already, Bacillus subtilis is indispensable in many industries, and many more innovations are expected
Younger generation gets sick earlier and more often than older generation
In spite of their advanced age, they are in the middle of life, healthy, active and mentally alert – they are referred to as the “young old”
How sleep deprivation can harm the brain
Sleep deprivation decreases the amount of a factor that protects neurons
A whole new order of bacteria could hold the key to improving biogas production
The discovery was made by researchers from Germany, Spain and the Netherlands
How to inactivate common cold viruses
In the cold season, cold viruses are everywhere. But we can do something about it
New approach to testing for long Covid
Blood vessels in the eye altered with persistent coronavirus symptoms
How minimal genetic differences can turn healthy food into a deadly danger
You are what you eat - this old saying could take on a new dimension according to latest research results
More news from our other portals
Major breakthrough in the development of electric vehicle batteries
New study finds ways to suppress lithium plating in automotive batteries for faster charging electric vehicles
Blender Bites launches at Walmart USA
The products are to be introduced in about 1,600 stores across the country
Benchtop NMR spectroscopy can accurately analyse pyrolysis oils
More accessible analysis could help develop the potential of bio-oils as an alternative to fossil fuels
Clean water from fog
A property known as photocatalytic memory ensures that this also functions when skies are overcast and at night
Research shows table salt could be the secret ingredient for better chemical recycling
Table salt as the key to the plastics recycling revolution?
Green, sweet and crisp - New apple variety Pia41 approved
The apple bred at the Julius Kühn Institute receives variety protection
Graphene discovery could help generate hydrogen cheaply and sustainably
Microscopic insights into electrochemical interfaces
Sugar: Small increase in production despite record prices
EU sugar market more than in need of reform to keep medium-sized processing companies competitive
Scientists use quantum device to slow down simulated chemical reaction 100 billion times
What happens in femtoseconds in nature can now be observed in milliseconds in the lab
Green methanol for shipping and industry: € 10.4 Mio. for the "Leuna100" project
A consortium of two Fraunhofer institutes, DBI-Gastechnologisches Institut Freiberg, Technical University of Berlin and C1 makes industrial history at the Leuna site
Stanford study shows how the meat and dairy sector resists competition from alternative animal products
New battery holds promise for green energy
Redox-flow battery eliminates costly and inefficient membrane
Fondant under the magnifying glass
New insights into the properties of sweet coating: The results could be used to optimize the industrial production process in the future
Leipzig-based start-up converts CO₂ into green chemicals with patented plasma catalysis
CO₂ recycling as a useful complement to carbon capture and storage
A microchip for Parmigiano Reggiano cheese
Consorzio del Parmigiano Reggiano, p-Chip Corporation, and Kaasmerk Matec Partner to Launch Breakthrough in Food-Safe Digital Tracking Technology
Cleaning water with ‘smart rust’ and magnets
New method for pollutants such as crude oil, glyphosate, microplastics and hormones
A Second Life for Electric Car Batteries
Scientists develop a decision model for retired lithium-ion batteries