Exopolysaccharide production in Ensifer meliloti laboratory and native strains and their effects on alfalfa inoculation


Bacterial surface molecules have an important role in the rhizobia-legume symbiosis. Ensifer meliloti (previously, Sinorhizobium meliloti), a symbiotic Gram-negative rhizobacterium, produces two different exopolysaccharides (EPSs), termed EPS I (succinoglycan) and EPS II (galactoglucan), with different functions in the symbiotic process. Accordingly, we undertook a study comparing the potential differences in alfalfa nodulation by E. meliloti strains with differences in their EPSs production. Strains recommended for inoculation as well as laboratory strains and native strains isolated from alfalfa fields were investigated. This study concentrated on EPS-II production, which results in mucoid colonies that are dependent on the presence of an intact expR gene. The results revealed that although the studied strains exhibited different phenotypes, the differences did not affect alfalfa nodulation itself. However, subtle changes in timing and efficacy to the effects of inoculation with the different strains may result because of other as-yet unknown factors. Thus, additional research is needed to determine the most effective inoculant strains and the best conditions for improving alfalfa production under agricultural conditions.

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Grants from the Secretaría de Ciencia y Técnica de la UNRC, Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT) and Consejo Nacional de Investigaciones Científicas y Técnicas of the República Argentina (CONICET) supported this work. EP and SC have a fellowship from the CONICET. FN, PB, and WG are Career Members of CONICET. Our thanks are due to Dr. Nicolás Ayub for helpful suggestions and useful discussions. Support from a Shanbrom Family Fund grant supported research on symbioses in arid environments in the Hirsch laboratory. This research was funded by FONCyT Grant number [PICT 1528/15].

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Primo, E.D., Cossovich, S., Nievas, F. et al. Exopolysaccharide production in Ensifer meliloti laboratory and native strains and their effects on alfalfa inoculation. Arch Microbiol (2019).

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  • Alfalfa
  • Sinorhizobium meliloti
  • Ensifer meliloti
  • Exopolysaccharides
  • Symbiosis
  • Biofertilization