Cyclolaminarinose. A new biologically active beta-(1-->3) cyclic glucan

Area of Science:

• Microbiology
• Carbohydrate Chemistry
• Molecular Biology

Background:

• Cyclic beta-glucans are important bacterial polysaccharides involved in various cellular functions.
• Previous studies on Rhizobium and Bradyrhizobium cyclic glucans identified specific structures and substituents.
• Mutants in Rhizobium meliloti's ndvB gene exhibit defects in symbiotic and osmotic adaptation.

Purpose of the Study:

• To isolate and characterize a unique cyclic beta-glucan from a recombinant Rhizobium meliloti strain.
• To elucidate the structure and properties of this novel glucan.
• To investigate the functional restoration of symbiotic and osmotic adaptation in a Rhizobium meliloti mutant by this glucan.

Main Methods:

• Isolation of the glucan from a perchloric acid cell extract using C-18 silica column chromatography.
• Structural elucidation using 2D NMR, FAB mass spectrometry, and high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD).
• Confirmation of structure through Smith degradation followed by NMR and mass spectrometry.

Main Results:

• A unique cyclic decasaccharide (cyclolaminarinose) was isolated, lacking phosphoglycerol or phosphocholine substituents.
• The glucan structure was confirmed as a cyclic beta-glucan with a specific substitution pattern.
• Synthesis of this glucan in the R. meliloti ndvB mutant restored wild-type symbiotic and hypoosmotic adaptation characteristics.

Conclusions:

• A novel cyclic beta-glucan with distinct structural features has been identified.
• This unique glucan plays a crucial role in restoring symbiotic and osmotic adaptation in Rhizobium meliloti.
• The findings contribute to understanding the diversity and function of bacterial cyclic beta-glucans.