Bacterial nitric oxide metabolism: recent insights in Rhizobia

Ana Salas, Juan J. Cabrera, Andrea Jiménez-Leiva, Socorro Mesa, Eulogio J. Bedmar, David J. Richardson, Andrew J. Gates, María J. Delgado (Lead Author)

Research output: Chapter in Book/Report/Conference proceedingChapter (peer-reviewed)peer-review

11 Citations (Scopus)
16 Downloads (Pure)


Nitric oxide (NO) is a reactive gaseous molecule that has several functions in biological systems depending on its concentration. At low concentrations, NO acts as a signaling molecule, while at high concentrations, it becomes very toxic due to its ability to react with multiple cellular targets. Soil bacteria, commonly known as rhizobia, have the capacity to establish a N2-fixing symbiosis with legumes inducing the formation of nodules in their roots. Several reports have shown NO production in the nodules where this gas acts either as a signaling molecule which regulates gene expression, or as a potent inhibitor of nitrogenase and other plant and bacteria enzymes. A better understanding of the sinks and sources of NO in rhizobia is essential to protect symbiotic nitrogen fixation from nitrosative stress. In nodules, both the plant and the microsymbiont contribute to the production of NO. From the bacterial perspective, the main source of NO reported in rhizobia is the denitrification pathway that varies significantly depending on the species. In addition to denitrification, nitrate assimilation is emerging as a new source of NO in rhizobia. To control NO accumulation in the nodules, in addition to plant haemoglobins, bacteroids also contribute to NO detoxification through the expression of a NorBC-type nitric oxide reductase as well as rhizobial haemoglobins. In the present review, updated knowledge about the NO metabolism in legume-associated endosymbiotic bacteria is summarized.
Original languageEnglish
Title of host publicationAdvances in Microbial Physiology
EditorsRobert K. Poole, David J. Kelly
Number of pages57
ISBN (Print)9780128246016
Publication statusPublished - 2021

Publication series

NameAdvances in Microbial Physiology
PublisherAcademic Press Inc.
ISSN (Print)0065-2911


  • Bacteroids
  • Denitrification
  • Hemoglobins
  • Nitrate assimilation
  • Nitrate reductase
  • Nitric oxide reductase
  • Regulation
  • Rhizobia-legume symbiosis
  • Root nodules

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