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Tag: Max Planck Institute for Marine Microbiology

  • Turning a poison into food

    Turning a poison into food

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    Newswise — Methanogens are microorganisms that produce methane when little or no oxygen is present in their surroundings. Their methane production – for example in the digestive tract of ruminants – is relevant for global carbon cycling, as methane is a very potent greenhouse gas, but can also be used as an energy source to heat our houses.

    A toxic base for growth

    The object of the study now published in Nature Chemical Biology are two 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). 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 poison for most organisms, it is essential for methanogens and they can tolerate even high concentrations of it. However, their Achilles’ heel is the toxic and reactive sulfur compound sulfite, which destroys the enzyme needed to make methane. In their environments, both investigated organisms are occasionally exposed to sulfite, for example, when oxygen enters and reacts with the reduced sulfide. Its partial oxidation results in the formation of sulfite, and thus the methanogens need to protect themselves. But how can they do this?

    A molecular snapshot of the process

    Marion Jespersen and Tristan Wagner from the Max Planck Institute for Marine Microbiology in Bremen, Germany, together with Antonio Pierik from the University of Kaiserslautern, now provide a snapshot of the enzyme detoxifying the sulfite. This butterfly-shaped enzyme ist known 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 growth. In the current study, Jespersen and her colleagues describe how the enzyme works. “The enzyme traps the sulfite and directly reduces it to sulfide, which can be incorporated, for example, into amino acids”, Jespersen explains (see figure). “As a result, the methanogen doesn’t get poisoned and even uses the product as its sulfur source. They turn poison into food!”

    It sounds simple. But in fact, Jespersen and her colleagues found that they were dealing with a fascinating and complicated overlap. “There are two ways of sulfite reduction: dissimilatory and assimilatory”, Jespersen explains. “The organism under study uses an enzyme that is built like a dissimilatory one, but it uses an assimilatory mechanism. It combines the best of both worlds, one could say, at least for its living conditions.”

    It is assumed that the enzymes from both the dissimilatory and the assimilatory pathway have evolved from one common ancestor. “Sulfite reductases are ancient enzymes that have a major impact 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 snapshot of this ancient primordial enzyme, an exciting look back in evolution.”

    Biotechnological applications in view

    The Fsr not only opens up evolutionary implications but also allows us to better understand the fascinating world of marine microbes. Methanogens that can grow only on sulfite circumvent the need to use the dangerous sulfide, their usual sulfur substrate. “This opens opportunities for safer biotechnological applications to study these important microorganisms. An optimal solution would be to find a methanogen that reduces sulfate, which is cheap, abundant, and a completely safe sulfur source”, says Wagner. In fact, this methanogen already exists, it is Methanothermococcus thermolithotrophicus. The researchers hypothesized that Fsr orchestrates the last reaction of this sulfate reduction pathway, because one of its intermediates would be sulfite. “Our next challenge is to understand how it can transform sulfate to sulfite, to get a complete picture of the capabilities of these miracle microbes.”

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    Max Planck Institute for Marine Microbiology

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  • Slime for the climate, delivered by brown algae

    Slime for the climate, delivered by brown algae

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    Newswise — Brown algae are true wonder plants when it comes to absorbing carbon dioxide from the air. They even outcompete forests on land in this, and thus play a decisive role for the atmosphere and our climate. But what happens to the carbon dioxide after the algae have absorbed it? Researchers at the Max Planck Institute for Marine Microbiology now report in the Proceedings of the National Academy of Sciences (PNAS) that the brown algae can remove large amounts of carbon dioxide from the global cycle in the long term and thus can counteract global warming.

    Fucoidan: Brown algae slime is not a favourite dish

    Algae take up carbon dioxide from the atmosphere and use the carbon to grow. They release up to a third of the carbon they absorb back into the seawater, for example in the form of sugary excretions. Depending on the structure of these excretions, they are either quickly used by other organisms or sink towards the seafloor.

    “The excretions of brown algae are very complex and therefore incredibly complicated to measure,” says first author Hagen Buck-Wiese from the Max Planck Institute for Marine Microbiology in Bremen. “However, we have managed to develop a method to analyse them in detail.” With this method, the researchers scrutinised a large number of different substances. The so-called fucoidan turned out to be particularly exciting. “Fucoidan made up about half of the excretions of the brown algae species we studied, the so-called bladderwrack,” says Buck-Wiese. Fucoidan is a recalcitrant molecule. “The fucoidan is so complex that it is very hard for other organisms to use it. No one seems to like it.” As a result, the carbon from the fucoidan does not return to the atmosphere quickly. “This makes the brown algae particularly good helpers in removing carbon dioxide from the atmosphere in the long term – for hundreds to thousands of years.”

    Brown algae could bind almost all of Germany’s carbon dioxide emissions

    Brown algae are remarkably productive. It is estimated that they absorb about 1 gigaton (one billion tons) of carbon per year from the air. Using the results of the present study, this would mean that up to 0.15 gigatons of carbon, equivalent to 0.55 gigatons of carbon dioxide, are sequestered by brown algae each year in the long term. For comparison: Germany’s annual greenhouse gas emissions currently amount to about 0.74 gigatons of carbon dioxide, according to the Federal Environment Agency (Umweltbundesamt, estimation for 2020).

    “And even better: The fucoidan does not contain any nutrients such as nitrogen,” Buck-Wiese explains further. Thus, the growth of the brown algae is not affected by the carbon losses.

    More species and sites

    For the current study, Buck-Wiese and his colleagues from the MARUM MPG Bridge Group Marine Glycobiology, which is based at both the Bremen Max Planck Institute and MARUM – Centre for Marine and Environmental Sciences at the University of Bremen, conducted their experiments at the Tvärminne Zoological Station in southern Finland. “Next we want to look into other brown algae species and other locations,” says Buck-Wiese. “The great potential of brown algae for climate protection definitely needs to be further researched and utilised.”

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    Max Planck Institute for Marine Microbiology

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