MSGID: 1:317/3 64acdadf   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Breathing poison: Microbial life on nitric oxide respiration    
    In a long-term culture, scientists find and characterize two new   
   microorganisms growing on the toxic gas nitric oxide, reducing it completely to   
   N2    
      
     Date:   
         July 10, 2023   
     Source:   
         Max Planck Institute for Marine Microbiology   
     Summary:   
         Nitric oxide (NO) is a central molecule in the global cycling   
         of nitrogen, and also toxic. Little is known about if and how   
         microbes can use NO as a substrate for growth. Scientists have   
         now managed to grow a microbial community dominated by two, so-far   
         unknown species on NO for more than four years (and counting) and   
         study their metabolism in great detail. Their research provides   
         insight into the physiology of NO- respiring microorganisms,   
         which have pivotal roles in the control of climate active gases,   
         waste removal, and the evolution of nitrate and oxygen respiration.   
      
      
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   FULL STORY   
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   Nitric oxide (NO) is a fascinating and versatile molecule, important   
   for all living things as well as the environment. It is highly reactive   
   and toxic, organisms use it as a signaling molecule, it depletes the   
   ozone layer in our planet's atmosphere, and it is the precursor of the   
   greenhouse gas nitrous oxide (N2O). Moreover, NO might have played   
   a fundamental role in the emergence and evolution of life on Earth,   
   as it was available as a high-energy oxidant long before there was oxygen.   
      
   Thus, despite its toxicity, it makes perfect sense that microbes use   
   NO to grow. However, research on the topic is scarce and, to date,   
   microbes growing on it have not been cultivated. That has now changed,   
   as reported by scientists around Paloma Garrido Amador and Boran Kartal   
   from the Max Planck Institute for Marine Microbiology in Bremen, Germany,   
   in the journal Nature Microbiology.   
      
   They have managed to enrich two yet unknown species of microorganisms   
   growing on NO in bioreactors and reveal exciting aspects of their   
   lifestyle.   
      
   From the wastewater tank to the bioreactor The study started off with   
   a trip to Bremen's wastewater treatment plant. "We collected sludge   
   from their denitrifying tank," Garrido Amador tells. "Back in our   
   lab, we added the sludge to one of our bioreactors and we started the   
   incubation by feeding it with NO." Bioreactors are designed and optimized   
   to grow microorganisms under controlled conditions, which closely mimic   
   their natural environment. This bioreactor setup was very challenging,   
   though, Garrido Amador reports, "Because NO is toxic, we needed special   
   equipment and had to take great care when handling them for our own   
   safety. Nevertheless, we managed to keep the cultures growing for   
   more than four years now -- and they are still happy and healthy!"   
   Two new microorganisms The living conditions in the bioreactor thus   
   favored microorganisms that could survive and grow anaerobically   
   with NO. "Eventually, two previously unknown species turned out to   
   dominate the culture," says Boran Kartal, group leader of the Microbial   
   Physiology Research Group the Max Planck Institute in Bremen. "We named   
   them Nitricoxidivorans perserverans and Nitricoxidireducens bremensis."   
   Garrido Amador adds, "From just two microorganisms growing on NO,   
   we gained valuable insight into how non-model microorganisms, in   
   particular NO-reducers grow. Some of our observations showed us that   
   these microbes did not conform to how model organisms -- organisms   
   which easily cultivated and thus extensively studied -- behave,   
   and showcased the limitations of metabolic predictions based solely   
   on genome analyses."  Importance in the environment and applications   
   for waste removal "Currently we know little about the contribution of   
   microorganisms growing on NO to nitrogen cycling in natural and engineered   
   environments," explains Kartal. "Nevertheless, we can speculate that these   
   microorganisms could potentially be feeding on NO and N2O released by   
   other microorganisms while removing nitrosative stress and minimizing the   
   emission of these climate active gases to the atmosphere."  The enriched   
   microorganisms converted NO to dinitrogen (N2) very efficiently.   
      
   "There were virtually no emissions of the greenhouse gas nitrous oxide,"   
   Kartal adds. The latter -- the sole production of N2 -- is particularly   
   relevant for application: Many other microorganisms convert NO to   
   nitrous oxide, which is a potent greenhouse gas. N2, in contrast, is   
   harmless. Thus, each molecule of NO that is transformed into N2 instead   
   of nitrous oxide is one less molecule adding to climate change.   
      
   In a next step, the Max Planck researchers are cultivating other   
   NO-respiring microorganisms using samples from natural and engineered   
   environments.   
      
   "Cultivation and enrichment of further NO-respiring microorganisms will   
   help to elucidate the evolution of N-oxide reduction pathways and the   
   enzymes involved.   
      
   It will also allow to decipher the role of NO in known and yet-unknown   
   processes of the nitrogen cycle and its importance in the natural and   
   engineered environments where these processes take place.," Garrido   
   Amador concludes.   
      
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   Story Source: Materials provided by   
   Max_Planck_Institute_for_Marine_Microbiology. Note: Content may be edited   
   for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Paloma Garrido-Amador, Niek Stortenbeker, Hans J. C. T. Wessels,   
      Daan R.   
      
         Speth, Inmaculada Garcia-Heredia, Boran Kartal. Enrichment and   
         characterization of a nitric oxide-reducing microbial community   
         in a continuous bioreactor. Nature Microbiology, 2023; DOI:   
         10.1038/s41564- 023-01425-8   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/07/230710113927.htm   
      
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