Autotrophs, such as plants and algae, get sulfur by transforming sulfate into sulfide, which can be included into biomass. As a result, it was previously thought that microorganisms known as methanogens, which are typically short on energy, would be not able to convert sulfate into sulfide.” Things got actually exciting when we measured the disappearance of sulfate as the organism grew. By characterizing the enzymes one-by-one, the scientists put together the very first sulfate assimilation pathway from a methanogen. “An easy, yet highly efficient strategy and most likely the reason why this methanogen is able to grow on sulfate.
Researchers at limit Planck Institute for Marine Microbiology have actually found that Methanothermococcus thermolithotrophicus, a methanogen previously believed incapable of converting sulfate into sulfide due to the procedures high energy expenses and damaging byproducts, can in truth grow on sulfate. The researchers found five genes encoding sulfate-reduction-associated enzymes in the methanogens genome, and by defining these enzymes, they put together the first sulfate assimilation path from a methanogen.
How a methanogenic microbe reassembles a metabolic pathway piece by piece to transform Sulfate into a cellular structure block.
Researchers have actually discovered that the methanogen Methanothermococcus thermolithotrophicus can convert sulfate into sulfide, defying previous assumptions. By identifying an unique sulfate assimilation path in this methanogen, the findings open up the possibility of much safer and more cost-efficient biogas production through genetic modification.
Sulfur, an essential building block of life
Sulfur is a fundamental aspect of life and all organisms require it to manufacture cellular materials. Autotrophs, such as plants and algae, obtain sulfur by transforming sulfate into sulfide, which can be integrated into biomass. This procedure requires a lot of energy and produces harmful intermediates and byproducts that require to be instantly changed. As an outcome, it was formerly thought that microorganisms referred to as methanogens, which are generally brief on energy, would be unable to transform sulfate into sulfide. It was assumed that these microorganisms, which produce half of the worlds methane, rely on other types of sulfur, such as sulfide.
A methanogen absorbing 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, thinking about the toxic intermediates and energetic expenses? Why is it the only methanogen that seems to be capable of growing on this sulfur types? Does this organism usage chemical techniques or a yet unidentified method to allow sulfate assimilation? Marion Jespersen and Tristan Wagner at the Max Planck Institute for Marine Microbiology have actually now discovered answers to these concerns and published them in the journal Nature Microbiology..
PhD trainee Marion Jespersen works on a fermenter in which M. thermolithotrophicus grows specifically on sulfate as sulfur source. Credit: Tristan Wagner/ Max Planck Institute for Marine Microbiology.
The very first difficulty the researchers satisfied was to get the microorganism to grow on the brand-new sulfur source. “When I began my PhD, I truly needed to persuade M. thermolithotrophicus to eat sulfate instead of sulfide,” says Marion Jespersen. “But after enhancing the medium, Methanothermococcus became a pro at growing on sulfate, with cell densities equivalent to those when growing on sulfide.”.
” Things got truly amazing when we determined the disappearance of sulfate as the organism grew. Now the scientists were all set to dig into the information of the underlying procedures.
The first molecular dissection of the sulfate assimilation path.
They found 5 genes that had the possible to encode sulfate-reduction-associated enzymes. “We managed to identify every one of those enzymes and for that reason explored the total pathway.
The cascade of chain reaction beginning with sulfate (SO42-) to sulfide (H2S). Credit: Marion Jespersen/ Max Planck Institute for Marine Microbiology.
By defining the enzymes one-by-one, the researchers put together the very first sulfate assimilation path from a methanogen. While the first two enzymes of the path are popular and happen in numerous microorganisms and plants, the next enzymes were of a new kind. “We were stunned to see that it appears as if M. thermolithotrophicus has actually hijacked one enzyme from a dissimilatory sulfate-reducing organism and slightly modified it to serve its own requirements,” states Jespersen. While some microbes assimilate sulfate as a cellular structure block, others utilize it to get energy in a dissimilatory procedure– as people do when respiring oxygen. The microorganisms that perform dissimilatory sulfate-reduction use a various set of enzymes to do so. The methanogen studied here transformed among these dissimilatory enzymes into an assimilatory one. “A basic, yet highly reliable strategy and more than likely the reason that this methanogen has the ability to grow on sulfate. So far, this particular enzyme has only been discovered in M. thermolithotrophicus and no other methanogens,” Jespersen explains.
M. thermolithotrophicus likewise needs to cope with two toxins that are created throughout the assimilation of sulfate. That ´ s what the last 2 enzymes of the path are produced: The very first one, once again similar to a dissimilatory enzyme, generates sulfide from sulfite. The second one is a brand-new type of phosphatase with robust effectiveness to hydrolyze the other poison, soon referred to as PAP..
” It seems that M. thermolithotrophicus gathered genetic information from its microbial environment that enabled it to grow on sulfate. By blending and matching dissimilatory and assimilatory enzymes, it developed its own functional sulfate reduction equipment,” states Wagner..
New opportunities for biotechnological application.
To do this, methanogens are grown in large bioreactors. A present bottleneck in the cultivation of methanogens is their requirement for the extremely hazardous and explosive hydrogen sulfide gas as a sulfur source.
” An unsolved burning concern 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 likewise revealed in the natural environment of the microbe”, concludes Wagner.
Recommendation: “Assimilatory sulfate-reduction in the marine methanogen Methanothermococcus thermolithotrophicus” 5 June 2023, Nature Microbiology.DOI: 10.1038/ s41564-023-01398-8.