Specific hopanoid classes differentially affect free-living and symbiotic states of Bradyrhizobium diazoefficiens

Kulkarni Gargi, Busset Nicolas, Molinaro Antonio, Gargani Daniel, Chaintreuil Clémence, Silipo Alba, Giraud Eric, Newman Dianne K.. 2015. Specific hopanoid classes differentially affect free-living and symbiotic states of Bradyrhizobium diazoefficiens. Mbio, 6 (5):e01251-15, 9 p.

Quartile : Q1, Sujet : MICROBIOLOGY

Résumé : A better understanding of how bacteria resist stresses encountered during the progression of plant-microbe symbioses will advance our ability to stimulate plant growth. Here, we show that the symbiotic system comprising the nitrogen-fixing bacterium Bradyrhizobium diazoefficiens and the legume Aeschynomene afraspera requires hopanoid production for optimal fitness. While methylated (2Me) hopanoids contribute to growth under plant-cell-like microaerobic and acidic conditions in the free-living state, they are dispensable during symbiosis. In contrast, synthesis of extended (C35) hopanoids is required for growth microaerobically and under various stress conditions (high temperature, low pH, high osmolarity, bile salts, oxidative stress, and antimicrobial peptides) in the free-living state and also during symbiosis. These defects might be due to a less rigid membrane resulting from the absence of free or lipidA-bound C35 hopanoids or the accumulation of the C30 hopanoid diploptene. Our results also show that C35 hopanoids are necessary for symbiosis only with the host Aeschynomene afraspera but not with soybean. This difference is likely related to the presence of cysteine-rich antimicrobial peptides in Aeschynomene nodules that induce drastic modification in bacterial morphology and physiology. The study of hopanoid mutants in plant symbionts thus provides an opportunity to gain insight into host-microbe interactions during later stages of symbiotic progression, as well as the microenvironmental conditions for which hopanoids provide a fitness advantage.

Mots-clés Agrovoc : Aeschynomene, symbiose, Bradyrhizobium, Fixation de l'azote, stress

Classification Agris : F62 - Physiologie végétale - Croissance et développement

Champ stratégique Cirad : Axe 1 (2014-2018) - Agriculture écologiquement intensive

Auteurs et affiliations

• Kulkarni Gargi, California Institute of Technology (USA)
• Busset Nicolas, IRD (FRA)
• Molinaro Antonio, Université de Naples 2 (ITA)
• Gargani Daniel, CIRAD-BIOS-UMR BGPI (FRA)
• Chaintreuil Clémence, IRD (FRA)
• Silipo Alba, Université de Naples 2 (ITA)
• Giraud Eric, IRD (FRA)
• Newman Dianne K., California Institute of Technology (USA)

Source : Cirad-Agritrop (https://agritrop.cirad.fr/578957/)

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