They obtain their cellular energy by producing methane and receive sulfur for growth in form of sulfide, that is present in their environments.
While sulfide is a toxin for most organisms, it is important for methanogens and they can endure even high concentrations of it. Their Achilles heel is the harmful and reactive sulfur compound sulfite, which ruins the enzyme required to make methane.
In their environments, both examined organisms are periodically exposed to sulfite, for example, when oxygen goes into and reacts with the reduced sulfide. Its partial oxidation leads to the formation of sulfite, and hence the methanogens require to protect themselves. How can they do this?
Marion Jespersen with the purified F420-dependent sulfite reductase (Fsr). The black color comes from all the iron associated with the response. Experiments are brought out in an anaerobic chamber and under synthetic light to protect the enzyme from oxygen and daytime. Credit: Tristan Wagner/Max Planck Institute for Marine Microbiology
A molecular picture of the process
Marion Jespersen and Tristan Wagner from limit Planck Institute for Marine Microbiology in Bremen, Germany, together with Antonio Pierik from the University of Kaiserslautern, now supply a picture of the enzyme detoxifying the sulfite. This butterfly-shaped enzyme is understood as the F420-dependent sulfite reductase or Fsr. It is capable of turning sulfite into sulfide– a safe source of sulfur that the methanogens require for development.
In the present study, Jespersen and her colleagues explain how the enzyme works. “The enzyme traps the sulfite and straight minimizes it to sulfide, which can be incorporated, for example, into amino acids”, Jespersen describes, “As an outcome, the methanogen does not get poisoned and even uses the product as its sulfur source. They turn toxin into food!”
“There are two ways of sulfite reduction: dissimilatory and assimilatory”, Jespersen explains. “The organism under research study uses an enzyme that is constructed like a dissimilatory one, but it uses an assimilatory system.
It is presumed that the enzymes from both the dissimilatory and the assimilatory paths have actually evolved from one common forefather. “Sulfite reductases are ancient enzymes that have a major effect on the global sulfur and carbon cycles”, adds Tristan Wagner, head of the Max Planck Research Group Microbial Metabolism at the Max Planck Institute in Bremen. “Our enzyme, the Fsr, is probably a picture of this ancient prehistoric enzyme, an exciting look back in evolution.”
Biotechnological applications in view
The Fsr not only opens up evolutionary ramifications however likewise allows us to better understand the interesting world of marine microorganisms. Methanogens that can grow only on sulfite circumvent the need to use the hazardous sulfide, their normal sulfur substrate.
” This opens opportunities for much safer biotechnological applications to study these essential microbes. An optimum service would be to find a methanogen that minimizes sulfate, which is low-cost, plentiful, and a totally safe sulfur source”, says Wagner.
This methanogen already exists, it is Methanothermococcus thermolithotrophicus. The scientists assumed that Fsr manages the last response of this sulfate reduction path because among its intermediates would be sulfite.
” Our next obstacle is to comprehend how it can transform sulfate to sulfite, to get a total image of the capabilities of these wonder microbes.”
Reference: “Structures of the sulfite detoxifying F420-dependent enzyme from Methanococcales” by Marion Jespersen, Antonio J. Pierik and Tristan Wagner, 19 January 2023, Nature Chemical Biology.DOI: 10.1038/ s41589-022-01232-y.
Illustration of Fsrs catalytic site where sulfite gets decreased to sulfide. In their environments, both investigated organisms are occasionally exposed to sulfite, for example, when oxygen responds and enters with the reduced sulfide. It is capable of turning sulfite into sulfide– a safe source of sulfur that the methanogens require for growth.
“The enzyme traps the sulfite and straight reduces it to sulfide, which can be included, for example, into amino acids”, Jespersen discusses, “As an outcome, the methanogen doesnt get poisoned and even uses the product as its sulfur source. “Sulfite reductases are ancient enzymes that have a major effect on the worldwide sulfur and carbon cycles”, includes Tristan Wagner, head of the Max Planck Research Group Microbial Metabolism at the Max Planck Institute in Bremen.
Illustration of Fsrs catalytic website where sulfite gets minimized to sulfide. The siroheme (in pink) that binds and converts the sulfite is embedded in a cavity of the protein (gray surface area) which is solvent available. This method, the sulfite can easily enter the protein and the produced sulfide can leave it. Credit: Max Planck Institute for Marine Microbiology
Researchers at the Max Planck Institute for Marine Microbiology have actually revealed how a methane-producing microorganism prospers on hazardous sulfite without becoming poisoned.
Methanogens are small organisms that generate methane in an oxygen-deprived environment. Their production of methane, such as in the digestive system of ruminants, plays a considerable function in the worldwide carbon cycle as methane is an extremely powerful greenhouse gas. Methane can also serve as an energy source for heating houses.
A harmful base for growth
The object of the research study now released in Nature Chemical Biology are 2 marine heat-loving methanogens: Methanothermococcus thermolithotrophicus ( lives in geothermally heated sediments at around 65 ° C) and Methanocaldococcus jannaschii ( prefers deep-sea volcanos with around 85 ° C).
