A survey of the energy metabolism of nodulating symbionts reveals a new form of respiratory complex I
2016
Degli Esposti, Mauro | Martinez Romero, Esperanza
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.
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