Characterization of water-soluble exopolysaccharides from Gluconacetobacter xylinus and their impacts on bacterial cellulose crystallization and ribbon assembly
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Gluconacetobacter xylinus has the ability to produce different types of water soluble exopolysaccharides (EPS). Those EPS have different levels of association to bacterial cellulose (BC). At least a portion of the EPS can be released from the BC by 0.1 to 4 M NaOH solution treatments. Hard to extract EPS (HE-EPS) released by 4 M NaOH solutions have been characterized and contain approximately 75 % mannose and 25 % glucose. To study the effect of the EPS on BC synthesis, purified EPS were added to the medium at the start of cultivation and the BC produced was characterized. Results showed that the presence of HE-EPS in the culture medium interfered with the alignment of the BC crystals, but did not reduce crystal size. This is in contrast to similar studies performed using xyloglucan, xylan and glucomannan. The width of the average ribbon increased by 60 % when HE-EPS levels increased in the medium, which indicated that the HE-EPS could also modulate the bundling of cellulose ribbons. Based on the data we propose a mechanism for how HE-EPS alters cellulose formation and assembly. The addition of HE-EPS disturbs the preferential crystal orientation and increases the spacing of cellulose microfibrils without affecting crystallization by associating with ordered cellulose prior to physical aggregation or bundling.
KeywordsExopolysaccharides Bacterial cellulose Ribbon assembly Cellulose crystallization
This material is based upon work supported as part of The Center for LignoCellulose Structure and Formation, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001090. The molecular weight estimation was performed by the Complex Carbohydrate Research Center, The University of Georgia, supported in part by the Department of Energy-funded (DE-FG09-93ER-20097) Center for Plant and Microbial Complex Carbohydrates.
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