Structural stability ofSclerotium rolfsiiATCC 201126 β-glucan with fermentation time: a chemical, infrared spectroscopic and enzymatic approach

Abstract

Aims: Sclerotium rolfsii ATCC 201126 exopolysaccharides (EPSs) recovered at 48 h (EPS I) and 72 h (EPS II) of fermentation, with differences in rheological parameters, hydrogel topography, salt tolerance, antisyneresis, emulsifying and suspending properties, were subjected to a polyphasic characterization in order to detect structural divergences. Methods and Results: Fermenter‐scale production led to productivity (Pr) and yield (YP/C) values higher at 48 h (Pr = 0·542 g l−1 h−1; YP/C = 0·74) than at 72 h (Pr = 0·336 g l−1 h−1; YP/C = 0·50). Both EPSs were neutral glucose‐homopolysaccharides with a β‐(1,3)‐glycosidic backbone and single β‐(1,6)‐glucopyranosyl sidechains regularly attached every three residues in the main chain, as revealed by chemical analyses. The infra‐red diagnostic peak at 890 cm−1 confirmed β‐glycosidic linkages, while gentiobiose released by β‐(1,3)‐glucanases confirmed single β‐1,6‐glycosidic branching for both EPSs. Conclusions: The true modular repeating unit of S. rolfsii ATCC 201126 scleroglucan could be resolved. Structural stability was corroborated and no structural differences could be detected as to account for the variations in EPSs behaviour. Significance and Impact of the Study: Recovery of S. rolfsii ATCC 201126 scleroglucan at 48 h might be considered based on better fermentation kinetic parameters and no detrimental effects on EPS structural features.

Microbial production of scleroglucan and downstream processing

“…When dissolved in water at room temperature and low concentrations of alkali, usually below 0.15 M NaOH, it can be assumed that scleroglucan adopts a highly ordered, rigid, triple helical tertiary structure ( Figure 1 ). Under this macromolecular conformation, protruding (1,6)- β-glycosidic side branching prevents the intermolecular approach by extensive H-bonding, which otherwise would lead to aggregated forms and precipitation (Fariña et al, 2001, 2009; Laroche and Michaud, 2007). Meanwhile, interstrand hydrogen bonding at the center of the triplex stabilizes the macromolecular structure (Atkins and Parker, 1968; Bluhm et al, 1982; Sletmoen et al, 2009).…”

“…Within this range, Sclerotium rolfsii ATCC 201126 scleroglucan exhibits an average MW of about 5.2 × 10 6 Da for the triplex and 1.6–1.7 × 10 6 Da for the random coil, in association to high intrinsic viscosities ([η] = 9510–9610 mL/g, for the triplex in water; Fariña et al, 2001). With reference to the degree of polymerization (DP), the reported values are variable from 110 for Sclerotium glucanicum scleroglucan (Bielecki and Galas, 1991), 800 for a commercial scleroglucan (Bluhm et al, 1982), 500–1600 for related glucans (Sandford, 1979), 2400–2500 for S. rolfsii ATCC 201126 scleroglucan (Fariña et al, 2009) and up to 5600 for another cited scleroglucan (Rice et al, 2004). …”

“…Nevertheless, slight to great variations of these properties may be seen depending on the producing strain, the polymer production process and the downstream processing, facts that might modify the MW, DP, DB, conformational parameters, and/or the polymer purity grade, and so will determine its final potential applications. For instance, we reported that low concentrations (e.g., 2 g/L) of pure (∼90–98% EPS) S. rolfsii ATCC 201126 scleroglucan in water are able to yield highly viscous solutions with non-Newtonian, non-thixotropic and pseudoplastic behavior (Fariña et al, 2001, 2009; Viñarta et al, 2007). …”

Investigation on the film-forming properties of lab fermenter scale produced scleroglucans from Sclerotium rolfsii ATCC 201126

“…Taking into account the advances on the knowledge of the physicochemical properties of S. rolfsii ATCC 201126 scleroglucan (Fariña et al, 2001;Fariña, Viñarta, Cattaneo, & Figueroa, 2009), the film-forming ability of different lab fermenter scale produced polysaccharides was examined based on different roomtemperature and freeze-thawing protocols for preparation.…”

Transcriptome sequencing and comparative transcriptome analysis of the scleroglucan producer Sclerotium rolfsii

“…Scleroglucan shows remarkable rheological properties rendering the substance as a multipurpose compound for many industrial applications, ranging from oil recovery over food industry to cosmetics and medical applications [5-7]. Surprisingly, only very little information is available on the biosynthesis of scleroglucan formation by S. rolfsii [4,7,8] whereas the physicochemical properties of scleroglucan are well explored [7-11]. …”