A survey of the energy metabolism of nodulating symbionts reveals a new form of respiratory complex I.
A limiting factor in agriculture is the availability of nitrogen in the soil, which may be compensated by biological N2 fixation catalysed by bacteria. Most biological N2 fixation occurs in root nodules of plants that respond to bacterial infection by establishing symbiosis with selected prokaryotes. The plants provide energy metabolites and a microoxic environment to the bacterial symbionts to facilitate their capacity of N2 fixation. Despite enormous advances in the molecular genetics of this symbiosis between plants and nodulating bacteria, we still do not understand fundamental aspects which determine the efficiency of N2 fixation in the nodules, and therefore the capacity to biologically enrich agricultural soils. Here we provide an overview of the central features of the energy metabolism that sustains N2 fixation, with emphasis on the bacterial respiratory chain supplying the electrons and ATP required for the nitrogenase reaction. We discuss common trends and specific variations in the integrated process of respiratory electron transport and N2 fixation. Among such variations we introduce green complex I, an ancient version of NADH:ubiquinone oxidoreductase that is present in several Rhizobiaceae and may facilitate N2 fixation.
['Degli Esposti|Mauro|M|', 'Martinez Romero|Esperanza|E|']
D001419:Bacteria D042967:Electron Transport Complex I D004734:Energy Metabolism D009584:Nitrogen D009586:Nitrogen Fixation D009591:Nitrogenase D010944:Plants D012230:Rhizobiaceae D053204:Root Nodules, Plant D012987:Soil D012988:Soil Microbiology D011795:Surveys and Questionnaires D013559:Symbiosis
nodulating symbionts ubiquinone TCA cycle nitrogen fixation respiratory complex I