Integrative genomic and structural diversity of exopolysaccharides produced by Leuconostoc isolates from sugar beet factories

Authors: JOSHI, SANJAY - Oak Ridge National Laboratory; Bruni, Gillian; Terrell, Evan; HUANG, LEI - University Of Georgia; HEISS, CHRISTIAN - University Of Georgia; AZADI, PARASTOO - University Of Georgia

Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2026
Publication Date: 5/25/2026
Citation: Joshi, S., Bruni, G.O., Terrell, E.C., Huang, L., Heiss, C., Azadi, P. 2026. Integrative genomic and structural diversity of exopolysaccharides produced by Leuconostoc isolates from sugar beet factories.. Carbohydrate Research. 567: Article 109978. https://doi.org/10.1016/j.carres.2026.109978.
DOI: https://doi.org/10.1016/j.carres.2026.109978

Interpretive Summary: In sugar beet factories, certain bacteria, such as Leuconostoc spp., produce sticky substances called exopolysaccharides (EPS) that thicken the sugar beet factory juice, clog filters, and make it more difficult to extract raw sugar. This slows production and raises manufacturing costs. In this study, we examined nine Leuconostoc strains from factories to identify the types of EPS produced and the proteins responsible for making EPS. We found EPS were composed mostly of glucose, forming a type of sugar polymer called dextran. Although all strains produced dextran, the structures varied, with some exhibiting a branching pattern, and one isolate, BSDF62-9, contained a different sugar called fructan. The size of these polymers also ranged from relatively small to extremely large (0.62–21.3 MDa), indicating dramatic differences in viscosity potential. These variations may help to explain differences in operational challenged caused by different bacteria. By comparing bacterial genomes, we discovered that the strains contain various genes encoding carbohydrate-active enzymes that produce these polymers. Some species had very similar sets of enzymes, while others were unique. Linking these genetic differences to the types and sizes of EPS produced provides a clearer understanding of EPS formation by sugar beet factory-derived Leuconostoc spp.

Technical Abstract: Exopolysaccharides (EPS) synthesized by Leuconostoc species are biopolymers that impact sugar beet processing efficiency in factories by causing operational challenges. There is also potential for utilizing these biopolymers in numerous biobased applications. Therefore, nine sugar beet factory-derived Leuconostoc isolates were characterized using integrative phenotypic and genomic analyses to elucidate the structural diversity and biosynthetic basis of EPS formation. Glycosyl composition analysis showed glucose as the predominant sugar residue, confirming all the EPS contain a-glucans. In addition, glycosyl linkage analysis identified a-1,6-linked dextran as the primary structural backbone, with varying degrees of branching and minor fructofuranosyl components in one strain. L. mesenteroides BSDF62-9 EPS contained 9.66% 2,6-linked fructofuranosyl residues, indicating the presence of fructans, while L. citreum BSDF5-1 showed a higher proportion of 3-linked glucopyranosyl residues (12%), linked to the presence of an alternansucrase. Physicochemical characterization revealed considerable variation in EPS molecular weight, ranging from 0.62 to 21.3 MDa, indicating profound size heterogeneity. Comparative genomics of nine sugar beet factory-derived Leuconostoc strains uncovered substantial differences in glucansucrase and fructansucrase gene content, particularly glycoside hydrolase family 70 (GH70) and 68 (GH68) enzymes. Notably, L. citreum BSDF5-1 separated distinctly from other isolates, indicating a unique CAZyme composition, while most L. suionicum isolates clustered tightly together, reflecting a conserved enzymatic toolkit among these strains. Hierarchical clustering of CAZyme profiles corroborated species-specific patterns. Furthermore, L. mesenteroides BSDF62-9 and L. suionicum BSDF2-6 also encode copies of levansucrase and were grouped separately from other strains. Taken together, this integrative analysis links genotype with structural properties of EPS.