Microevolution Rather than Large Genome Divergence Determines the Effectiveness of Legume–Rhizobia Symbiotic Interaction Under Field Conditions

JOZEFKOWICZ, CINTIA; BRAMBILLA, SILVINA; FRARE, ROMINA; STRITZLER, MARGARITA; PUENTE, MARIANA; PICCINETTI, CARLOS; SOTO, GABRIELA; AYUB, NICOLÁS

JOURNAL OF MOLECULAR EVOLUTION

SPRINGER

Lugar: Berlin; Año: 2017

0022-2844

Despite the vast screening for natural nitrogenfixingisolates by public and private consortia, no significantprogresses in the production of improved nitrogenfixinginoculants for alfalfa production have been made inthe last years. Here, we present a comprehensive characterizationof the nitrogen-fixing strain Ensifer melilotiB399 (originally named Rhizobium meliloti 102F34),probably the inoculant most widely used in alfalfa productionsince the 1960s. Complete nucleotide sequence andgenome analysis of strain B399 showed that the threereplicons present in this commercial strain and the modelbacterium Ensifer meliloti 1021 are extremely similar toeach other in terms of nucleotide identity and syntenyconservation. In contrast to that observed in B399-treatedplants, inoculation of plants with strain 1021 did notimprove nitrogen content in different alfalfa cultivars underfield conditions, suggesting that a small genomic divergencecan drastically impact on the symbiotic phenotype.Therefore, in addition to the traditional screening of naturalnitrogen-fixing isolates, the genome engineering of modelstrains could be an attractive strategy to improve nitrogenfixation in legume crops.