Absence of the nitrous oxide reductase gene cluster in commercial alfalfa inoculants is probably due to the extensive loss of genes during rhizobial domestication

As other legume crops, alfalfa cultivation increases the emission of the greenhouse gas nitrous oxide (N2O). Since legumesymbiotic nitrogen-fixing bacteria play a crucial role in this emission, it is important to understand the possible impacts of rhizobial domestication on the evolution of denitrification genes. In comparison with the genomes of non-commercial strains, those of commercial alfalfa inoculants exhibit low total genome size, low number of ORFs and high numbers of both frameshifted genes and pseudogenes, suggesting a dramatic loss of genes during bacterial domestication. Genomic analysis focused on denitrification genes revealed that commercial strains have perfectly conserved the nitrate (NAP), nitrite (NIR) and nitric (NOR) reductase clusters related to the production of N2O from nitrate but completely lost the nitrous oxide (NOS) reductase cluster (nosRZDFYLX genes) associated with the reduction of N2O to gas nitrogen. Based on these results, we propose future screenings for alfalfa-nodulating isolates containing both nitrogen fixation and N2O reductase genes for environmental sustainability of alfalfa production.

Instituto de Genética

Fil: Brambilla, Silvina Maricel. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Genética "Ewald A. Favret"; Argentina

Fil: Frare, Romina Alejandra. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Genética "Ewald A. Favret"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Fil: Soto, Gabriela Cinthia. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Genética "Ewald A. Favret"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Fil: Jozefkowicz, Cintia. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Genética "Ewald A. Favret"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Fil: Ayub, Nicolás Daniel. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Genética "Ewald A. Favret"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina