Description of the Wild Strain Rhizobium rosettiformans DSM26376, Reclassified under Peteryoungia rosettiformans comb.nov., for Producing Glucuronan

Abstract

Glucuronan is a polysaccharide composed of β-(1,4)-linked d-glucuronic acids having intrinsic properties and biological activities recoverable in many fields of application. Currently, the description of Sinorhyzobium meliloti M5N1CS mutant bacterial strain as the sole source of glucuronan makes it relevant to the exploration of new microorganisms producing glucuronan. In this study, the Peteryoungia rosettifformans strain (Rhizobia), was identified as a wild producer of an exopolysaccharide (RhrBR46) related to glucuronan. Structural and biochemical features, using colorimetric assays, Fourier infrared spectroscopy, nuclear magnetic resonance, high pressure size exclusion chromatography coupled to multi-angle light laser scattering, and enzymatic assays allowed the characterization of a polyglucuronic acid, having a molecular mass (Mw¯) of 1.85 × 10⁵ Da, and being partially O-acetylated at C-2 and/or C-3 positions. The concentration of Mg²⁺ ions in the cultivation medium has been shown to impact the structure of RhrBR46, by reducing drastically its Mw¯ (73%) and increasing its DA (10%). Comparative structural analyses between RhrBR46 and the glucuronan from Sinorhyzobium meliloti M5N1CS strain revealed differences in terms of molecular weight, degree of acetylation (DA), and the distribution of acetylation pattern. These structural divergences of RhrBR46 might contribute to singular properties or biological activities of RhrBR46, offering new perspectives of application.

Keywords: Peteryoungia rosettiformans; exopolysaccharide; glucuronan; glucuronan lyase; rhizobium.

Figure 1

Biomass production (OD₆₀₀ (●) and dry weights (○)) and EPS production (▲) during cultivation of Peteryoungia rosettiformans DSM26376.

Figure 2

FTIR footprint spectra of RhrBR46 (black line) and RhrBR46-Mg (dark red dotted line). The wavenumbers of peaks are indicated.

Figure 3

Analysis of the TrGL glucuronan lyase activity (from Trichoderma reesei) on RhrBR46, RhrBR46-Mg and SmPGU (reference) substrates and their deacetylated forms. All assays were carried out in triplicate (n = 3).