Covalently linked hopanoid-lipid A improves outer-membrane resistance of a Bradyrhizobium symbiont of legumes

Alba Silipo (1) , Giuseppe Vitiello (1) , Djamel Gully (2) , Luisa Sturiale (3) , Clémence Chaintreuil (2) , Joel Fardoux (2) , Daniel Gargani (4, 5) , Hae-In Lee (6) , Gargi Kulkarni (7, 8) , Nicolas Busset (2) , Roberta Marchetti (1) , Angelo Palmigiano (3) , Herman Moll (9) , Regina Engel (9) , Rosa Lanzetta (1) , Luigi Paduano (1) , Michelangelo Parrilli (1) , Woo-Suk Chang (10, 6) , Otto Holst (9) , Dianne K. Newman (7, 8) , Domenico Garozzo (3) , Gerardino d'Errico (1) , Eric Giraud (2) , Antonio Molinaro (1)

1 Dipartimento di Scienze Chimiche, Complesso Universitario Monte Sant’Angelo
2 UMR LSTM - Laboratoire des symbioses tropicales et méditerranéennes
3 CNR - National Research Council of Italy | Consiglio Nazionale delle Ricerche
4 Biologie et Génétique des interactions Plantes-parasites pour la Protection Intégrée
5 Cirad - Centre de Coopération Internationale en Recherche Agronomique pour le Développement
6 University of Texas at Arlington
7 Division of Biology and Biological Engineering
8 HHMI - Howard Hughes Medical Institute
9 Leibniz-Center for Medicine and Biosciences
10 Chonbuk National University

Lipopolysaccharides (LPSs) are major components of the outer membrane of Gram-negative bacteria and are essential for their growth and survival. They act as a structural barrier and play an important role in the interaction with eukaryotic hosts. Here we demonstrate that a photosynthetic Bradyrhizobium strain, symbiont of Aeschynomene legumes, synthesizes a unique LPS bearing a hopanoid covalently attached to lipid A. Biophysical analyses of reconstituted liposomes indicate that this hopanoid-lipid A structure reinforces the stability and rigidity of the outer membrane. In addition, the bacterium produces other hopanoid molecules not linked to LPS. A hopanoid-deficient strain, lacking a squalene hopene cyclase, displays increased sensitivity to stressful conditions and reduced ability to survive intra-cellularly in the host plant. This unusual combination of hopanoid and LPS molecules may represent an adaptation to optimize bacterial survival in both free-living and symbiotic states.

Mots clés: identification; mechanism; agrobacterium; bacteria; gene; fatty-acid; mass-spectrometry; photosynthetic bradyrhizobia

Mots clés: lipopolysaccharide; absolute-configuration

Domaines: Biologie végétale; Sciences agricoles

Alba Silipo, Giuseppe Vitiello, Djamel Gully, Luisa Sturiale, Clémence Chaintreuil, et al.. Covalently linked hopanoid-lipid A improves outer-membrane resistance of a Bradyrhizobium symbiont of legumes. Nature Communications, 2014, 5, ⟨10.1038/ncomms6106⟩. ⟨hal-02632287⟩