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ARS Home » Southeast Area » New Orleans, Louisiana » Southern Regional Research Center » Commodity Utilization Research » Research » Publications at this Location » Publication #405652

Research Project: Improved Conversion of Sugar Crops into Food, Biofuels, Biochemicals, and Bioproducts

Location: Commodity Utilization Research

Title: Characterization of levan fructan produced by a Gluconobacter japonicus strain isolated from a sugarcane processing facility

Author
item Bruni, Gillian
item Qi, Yunci
item Terrell, Evan
item DUPRE, REBECCA - OAK RIDGE INSTITUTE FOR SCIENCE AND EDUCATION (ORISE)
item Mattison, Chris

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2024
Publication Date: 1/5/2024
Citation: Bruni, G.O., Qi, Y., Terrell, E., Dupre, R.A., Mattison, C.P. 2024. Characterization of levan fructan produced by a Gluconobacter japonicus strain isolated from a sugarcane processing facility. Microorganisms. 12(1). Article 107. https://doi.org/10.3390/microorganisms12010107.
DOI: https://doi.org/10.3390/microorganisms12010107

Interpretive Summary: Here we report the characterization of exopolysaccharide (EPS) from the bacterium Gluconobacter bacterium strain LASM12 that we previously isolated from a Louisiana sugarcane factory. Bacterial degradation of sucrose and production of problematic EPS have long been recognized at sugarcane factories, but recent research suggests that fructan-type EPS are more abundant than previously thought. Genome sequencing and analysis indicated that G. japonicus LASM12 has two levansucrase genes in its genome which were predicted to function in levan production. Therefore, additional experiments were conducted to further study this levan producer, including proteomics, growth comparison on various sugar substrates for EPS production, and conventional carbohydrate chemical analysis methods that confirm the identity of G. japonicus LASM12 EPS as levan fructan polysaccharide. This is the first in-depth study of a bona fide levan-producing bacterium isolated from Louisiana sugarcane factories.

Technical Abstract: Here we report the characterization of exopolysaccharide (EPS) from a fructan-forming Gluconobacter bacterium that we previously isolated from a Louisiana sugarcane factory. Whole genome sequencing identified the organism as Gluconobacter japonicus as well as the presence of two encoded levansucrase genes. One levansucrase protein was detected in the secreted protein fraction of G. japonicus LASM12 by QTOF LC-MS. Spotting assays on various sugar sources indicates that G. japonicus produces exopolysaccharide using sucrose and raffinose as substrates but not monosaccharides such as glucose or fructose. Spectral analysis of G. japonicus EPS correlated with levan fructan commercial standards by 1H-NMR, and with the characteristic carbohydrate fingerprint region for levan fructan by FTIR indicating that G. japonicus EPS is indeed levan fructan. Furthermore, glycosyl composition and glycosyl linkage analysis revealed a linear beta-2,6-fructofuranosyl polysaccharide with occasional (5.7%) beta-1,6-fructofuranosyl branches. Gel permeation chromatography of the levan fructan EPS showed two peaks at 4.5 kDa and 8 kDa.