The discovery of a bacteria that thrives on nitrogen while also creating methane
Researchers at the Max Planck Institute for Marine Microbiology have improved cultivation of a microbe that fixes nitrogen while creating methane and ammonia, and they have uncovered intriguing features of the organism’s biochemistry.
Carbon and nitrogen are the building blocks of all living things. Methanothermococcus thermolithotrophicus is one of the organisms that play a crucial role in the recycling of both of these elements. An equally convoluted microorganism bears this name. The methanogen M. thermolithotrophicus thrives in warm maritime environments.
It prefers temperatures of roughly 65 °C and can be found in the sediments of the ocean everywhere from the shallows to the deep sea. By combining hydrogen with nitrogen and carbon dioxide, it produces ammonia and methane. Both ammonia and methane have promising biotechnological uses in the production of fertilizers and alternative fuels.
At the Max Planck Institute for Marine Microbiology, researchers Tristan Wagner and Nevena Masla have accomplished the difficult task of cultivating this bacteria in a fermenter.
The research was conducted by Masla as part of her Ph.D. thesis; she explains that it is quite complicated to produce the optimal conditions for this bacterium to survive while fixing N2, including high temperatures, no oxygen, and careful monitoring of hydrogen and carbon dioxide levels. However, with some creativity and hard work, they were able to get them to flourish in their lab, producing the highest cell densities ever reported.
Once the cultures were established, the researchers could explore further into the organism by examining its physiology and, later, its metabolism as it adapted to N2-fixation. Masla explains that they were able to better understand M. thermolithotrophicus’s metabolism by working closely with their colleagues Chandni Sidhu and Hanno Teeling to conduct a range of physiological tests in conjunction with differential transcriptomics.
Some of M. thermolithotrophicus’ metabolic traits are intriguing. Methanogenesis, a process with its roots in the early anoxic Earth, is how these microorganisms obtain their cellular energy. When compared to humans, who use oxygen to convert glucose into carbon dioxide, methanogens get only a tiny bit of their energy via methanogenesis. Ironically, they would wear themselves out trying to fix nitrogen because it takes so much energy.
Tristan Wagner, head of the Max Planck Research Group Microbial Metabolism, and the study’s senior author, compares them to bumblebees, which are theoretically too heavy to fly yet clearly able to do so, nonetheless. However, despite their energy constraints, these interesting bacteria have been discovered to be the primary nitrogen fixers in several ecosystems.
Nitrogenase is the name for the enzyme that helps living things fix nitrogen. Molybdenum is a necessary cofactor for the reaction of the majority of nitrogenases. Bacteria that operate as symbionts in plant roots have been investigated extensively for their molybdenum nitrogenase. Whilst tungstate is effective in inhibiting their nitrogenase, it also has a number of other effects.
Scientists from Bremen discovered, somewhat unexpectedly, that tungstate does not inhibit the growth of M. thermolithotrophicus when it is fed nitrogen. Their microbe required only molybdenum to fix nitrogen and was unaffected by tungstate, so its metal-acquisition machinery must have evolved to make it more versatile, as Masla puts it.
The primary mechanism by which nitrogen is introduced into the biochemical cycle is known as nitrogen fixation. This is accomplished by the Haber-Bosch process, which artificially fixes nitrogen to make ammonia with hydrogen at very high temperatures and pressures for use in industrial fertilizer manufacturing. Most of the ammonia used as a fertilizer worldwide is produced from this material.
Using the Haber-Bosch method requires a great deal of power: It uses 2% of worldwide energy production while contributing to up to 1.4% of global carbon emissions. Because of this, people are trying to find greener ways to create ammonia.
Wagner believes that the technique utilized by M. thermolithotrophicus demonstrates that there are still options in the microbial world that can allow for more effective synthesis of ammonia, and that they might even be integrated with biofuel generation through methane.
Wagner said they understood that under nitrogen-fixing conditions, the methanogen reduces its production of proteins to promote nitrogen capture, a particularly smart technique of energy reallocation. Researchers will investigate the enzymes and molecular mechanisms of this process, in addition to expanding their investigation to other metabolic pathways in the organism.
Keywords: bacteria that thrives on nitrogen while also creating methane
Nevena Maslać et al. (2022). Comparative Transcriptomics Sheds Light on Remodeling of Gene Expression during Diazotrophy in the Thermophilic Methanogen Methanothermococcus thermolithotrophicus, mBio (2022). DOI: 10.1128/mbio.02443-22
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