(228dd) Effect of Sucrose Concentration on Levan Molecular Weight from Different Bacteria

Alvaro G. Garcinuño, Antonio Tabernero, Jose M. Sanchez-Álvarez , Miguel A. Galan, Eva M. Martin Del Valle

Department of Chemical Engineering. University of Salamanca. 

Levan is biopolymer formed by furanoses units (fructose) that shows a great potential for different applications such as industry, cosmetics, medicine or nanotechnology.

Levan has been traditionally obtained from Zymomonas mobilis, a gram negative bacterium, by culturing with high sucrose concentration. An enzyme located in its cell wall (Levansucrse) catalyzes the sucrose breakdown and fructose obtained is polymerized in order to build levan polymer. Levan has been proposed as a good polymer for nanoparticle formation. Particularly, due to its ability for nanoparticle formation by self-assembly; because of its hydrophobic and hydrophilic character.

One crucial factor for nanoparticle formation is related with polymer molecular weight. Moreover, it has been reported that molecular weight is also important for its antitumor activity [1]. For that reason, the main objective of this work is controlling levan molecular weight by modifying the culture medium.

Specifically, the effect of sucrose concentration on levan synthesis (and its molecular weight) from two no-studied bacteria (Bacillus atrophaeus and Acinetobacter nectaris, gram positive and gram negative respectively) is studied. It is found that A. nectaris growth and levan production are affected by sucrose concentration; wheras B. atrophaeus growth and levan production are not affected by modifying that parameter.

On the other hand, levan molecular weight from A. nectaris is considerably modified by sucrose concentration in culture medium (from 2000 kDa to 8000 kDa depending on sucrose amount), whereas levan from B. atrophaeus has a constant value around 50 kDa.

Studies with glucose (a by-product from sucrose hydrolysis) were carried out in order to study why that difference happens. It was found that glucose inhibits levansucrase in Gram negative bacteria (A. nectaris) and has no effect on levansucrase from Gram positive bacteria (B. atrophaeus). That inhibition could explain why polymer from Gram negative is longer than the obtained from Gram positive. Bacterial peptidoglycan wall acts as a barrier for starting new polymer chain, so that; polymerization has to continue with the chain that is being synthetized. These results allow controlling levan molecular weight by modifying sugar amount in culture medium.

References:

[1] Calazans G, Lima R, de França FP, Lopes CE. (2000). Molecular weight and antitumour activity of Zymomonas mobilis levans.