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Structural characterization of extracellular polysaccharides of Azorhizobium caulinodans and importance for nodule initiation on Sesbania rostrata
Author(s) -
D’Haeze Wim,
Glushka John,
De Rycke Riet,
Holsters Marcelle,
Carlson Russell W.
Publication year - 2004
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2004.03989.x
Subject(s) - biology , extracellular polysaccharide , nodule (geology) , microbiology and biotechnology , polysaccharide , symbiosis , sesbania , botany , biochemistry , bacteria , genetics , paleontology
Summary During lateral root base nodulation, the microsymbiont Azorhizobium caulinodans enters its host plant, Sesbania rostrata , via the formation of outer cortical infection pockets, a process that is characterized by a massive production of H 2 O 2 . Infection threads guide bacteria from infection pockets towards nodule primordia. Previously, two mutants were constructed that produce lipopolysaccharides (LPSs) similar to one another but different from the wild‐type LPS, and that are affected in extracellular polysaccharide (EPS) production. Mutant ORS571‐X15 was blocked at the infection pocket stage and unable to produce EPS. The other mutant, ORS571‐oac2, was impaired in the release from infection threads and was surrounded by a thin layer of EPS in comparison to the wild‐type strain that produced massive amounts of EPS. Structural characterization revealed that EPS purified from cultured and nodule bacteria was a linear homopolysaccharide of α‐1,3‐linked 4,6‐O‐(1‐carboxyethylidene)‐ d ‐galactosyl residues. In situ H 2 O 2 localization demonstrated that increased EPS production during early stages of invasion prevented the incorporation of H 2 O 2 inside the bacteria, suggesting a role for EPS in protecting the microsymbiont against H 2 O 2 . In addition, ex planta assays confirmed a positive correlation between increased EPS production and enhanced protection against H 2 O 2 .