Biological nitrogen fixation by alternative nitrogenases in boreal cyanolichens importance of molybdenum availability and implications for current biological nitrogen fixation estimates

• Published in: The New phytologist Vol. 213; no. 2; pp. 680 - 689
• Main Authors: Darnajoux, Romain, Zhang, Xinning, McRose, Darcy L., Miadlikowska, Jolanta, Lutzoni, François, Kraepiel, Anne M. L., Bellenger, Jean‐Philippe
• Format: Journal Article
• Language: English
• Published: England New Phytologist Trust 01-01-2017; Wiley Subscription Services, Inc
• Subjects: alternative nitrogenases; Availability; biological nitrogen fixation; boreal forest; Cyanobacteria; Cyanobacteria - drug effects; Cyanobacteria - metabolism; cyanolichens; Discriminant Analysis; Ecosystems; Environmental Pollution; Forest ecosystems; Lichens; Lichens - drug effects; Lichens - enzymology; Lichens - microbiology; Limiting factors; Linear Models; Molybdenum; molybdenum (Mo); Molybdenum - pharmacology; Nitrogen; Nitrogen cycle; Nitrogen fixation; Nitrogen Fixation - drug effects; Nitrogen Isotopes; Nitrogenase; Nitrogenase - metabolism; Nitrogenation; Nostoc; Peltigera aphthosa; Peltigera aphthosa s.l; Sweden; Symbionts; Symbiosis - drug effects; Temperate forests; Tropical climate; Tropical forests; Vanadium; vanadium (V); Vanadium - pharmacology; boreal forest; vanadium (V); cyanolichens; Peltigera aphthosa s.l; biological nitrogen fixation; alternative nitrogenases; molybdenum (Mo)
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.14166

Cryptogamic species and their associated cyanobacteria have attracted the attention of bio-geochemists because of their critical roles in the nitrogen cycle through symbiotic and asymbiotic biological fixation of nitrogen (BNF). BNF is mediated by the nitrogenase enzyme, which, in its most common form, requires molybdenum at its active site. Molybdenum has been reported as a limiting nutrient for BNF in many ecosystems, including tropical and temperate forests. Recent studies have suggested that alternative nitrogenases, which use vanadium or iron in place of molybdenum at their active site, might play a more prominent role in natural ecosystems than previously recognized.
Here, we studied the occurrence of vanadium, the role of molybdenum availability on vanadium acquisition and the contribution of alternative nitrogenases to BNF in the ubiquitous cyanolichen Peltigera aphthosa s.l.
We confirmed the use of the alternative vanadium-based nitrogenase in the Nostoc cyanobiont of these lichens and its substantial contribution to BNF in this organism. We also showed that the acquisition of vanadium is strongly regulated by the abundance of molybdenum.
These findings show that alternative nitrogenase can no longer be neglected in natural ecosystems, particularly in molybdenum-limited habitats.