Effect of chemical modifications of tannins on their antimicrobial and antibiofilm effect against Gram-negative and Gram-positive bacteria.

Background: Tannins have demonstrated antibacterial and antibiofilm activity, but there are still unknown aspects on how the chemical properties of tannins affect their biological properties. We are interested in understanding how to modulate the antibiofilm activity of tannins and in delineating the relationship between chemical determinants and antibiofilm activity. Materials and methods: The effect of five different naturally acquired tannins and their chemical derivatives on biofilm formation and planktonic growth of Salmonella Typhimurium, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus was determined in the Calgary biofilm device. Results: Most of the unmodified tannins exhibited specific antibiofilm activity against the assayed bacteria. The chemical modifications were found to alter the antibiofilm activity level and spectrum of the tannins. A positive charge introduced by derivatization with higher amounts of ammonium groups shifted the anti-biofilm spectrum toward Gram-negative bacteria, and derivatization with lower amounts of ammonium groups and acidifying derivatization shifted the spectrum toward Gram-positive bacteria. Furthermore, the quantity of phenolic OH-groups per molecule was found to have a weak impact on the anti-biofilm activity of the tannins. Conclusion: We were able to modulate the antibiofilm activity of several tannins by specific chemical modifications, providing a first approach for fine tuning of their activity and antibacterial spectrum.

Chemical Derivatization of Commercially Available Condensed and Hydrolyzable Tannins.

Novel valorization routes for tannins were opened by the development of a simple, straightforward, robust, and flexible approach to the selective functionalization of condensed and hydrolyzable tannins. Irrespective of the different degrees of polymerization, different commercial tannins were efficiently functionalized by the generation of an ether linkage bound to a short linker carrying the desired functional group. Functionalizations could be realized at varying degrees of technical loadings, i.e., amounts of introduced tannin-alien functionalities per number of phenolic hydroxyl groups. The same strategy was found suitable for the synthesis of polyethylene glycol-functionalized tannin copolymers. Condensed tannins functionalized with carboxylic acid moieties could be converted into a tannin-oligopeptide hybrid.

An Analytical Toolbox for Fast and Straightforward Structural Characterisation of Commercially Available Tannins.

Both condensed and hydrolysable tannins represent versatile natural polyphenolic structures exhibiting a broad range of activities that could be exploited in various fields including nutraceutics, cosmesis, consumer care, household and pharmaceutical applications. Various tannins are commercially available nowadays for use in such application fields. We have analysed a representative selection of commercially available condensed and hydrolysable tannins for structural features and purity. Using a combination of quantitative 31P NMR spectroscopy, HSQC measurements, MALDI-ToF analyses, gel permeation chromatography and wet chemical analysis, detailed structural characterisations and descriptions were possible, allowing for verification and falsification of claimed structural features.

The involvement of hexokinase in the coordinated regulation of glucose and gibberellin on cell wall invertase and sucrose synthesis in grape berry.

In plants, hexokinase (HXK, EC 2.7.1.1), an enzyme normally involved in hexose phosphorylation, plays an important role in sugar sensing and signaling. The hexokinase activity of grape HXKs was confirmed by functional complementation of the hexokinase-deficient yeast strain YSH7.4-3C (hxk1, hxk2, glk1). HXK1 and HXK2 were able to complement this mutant. The subcellular localization of HXK1 and HXK2, observed with green fluorescent protein fusion constructs, indicated that HXK1 localized to the cytosol while HXK2 was a nuclear-targeted hexokinase. Gibberellin (GA3) control various processes across plant life and has been involved in sugar accumulation. The coordinated regulation of exogenous GA3 with Glc on CWINV, SuSy1, or SuSy2 expressions indicated that GA3 can relieve the repression of Glc on CWINV or SuSy1 expression, and the repression of GA3 on SuSy2 expression overrides the Glc-inductive effect, resulting in the down-regulation of SuSy2 expression. It was concluded that GA3 negatively interfere with Glc signal transduction depending on hexokinase phosphorylation. GA3 might regulate CWINV, SuSy1 or SuSy2 expression to in order to maintain an intracellular sugar levels and normal cell metabolism. Our results provide new insights into the crosstalk mechanism of GA3 and Glc signaling depending on hexokinase in grape berry sugar accumulation.