Fenton reaction facilitates organic nitrogen acquisition by an ectomycorrhizal fungus

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Abstract

Boreal trees rely on their ectomycorrhizal fungal symbionts to acquire growth-limiting nutrients, such as nitrogen (N), which mainly occurs as proteins complexed in soil organic matter (SOM). The mechanisms for liberating this N are unclear as ectomycorrhizal fungi have lost many genes encoding lignocellulose-degrading enzymes present in their saprotrophic ancestors. We hypothesized that hydroxyl radicals (bullOH), produced by the ectomycorrhizal fungus Paxillus involutus during growth on SOM, are involved in liberating organic N. Paxillus involutus was grown for 7 d on N-containing or N-free substrates that represent major organic compounds of SOM. bullOH production, ammonium assimilation, and proteolytic activity were measured daily. bullOH production was strongly induced when P. involutus switched from ammonium to protein as the main N source. Extracellular proteolytic activity was initiated shortly after the oxidation. Oxidized protein substrates induced higher proteolytic activity than unmodified proteins. Dynamic modeling predicted that bullOH production occurs in a burst, regulated mainly by ammonium and ferric iron concentrations. We propose that the production of bullOH and extracellular proteolytic enzymes are regulated by similar nutritional signals. Oxidation works in concert with proteolysis, improving N liberation from proteins in SOM. Organic N mining by ectomycorrhizal fungi has, until now, only been attributed to proteolysis.

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Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Microbiology
  • Botany

Keywords

  • Fenton reaction, Nitrogen (N), Paxillus involutus, Proteolysis, Soil organic matter (SOM)
Original languageEnglish
Pages (from-to)335-343
JournalNew Phytologist
Volume218
Issue number1
Early online date2018 Jan 3
Publication statusPublished - 2018
Publication categoryResearch
Peer-reviewedYes