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Marine-Derived Bioactive Polysaccharides from Microorganisms
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Edité par CCSD -
In the search of novel fine chemicals and biopharmaceuticals, bacterial polysaccharides offer a source of safe, biocompatible, biodegradable and renewable products with specific biological functions. The bacteria that produce polysaccharides are also a source of key enzymes for the production of tailor-made polysaccharides in the high-value medical field. In the biotechnological challenge for the discovery of original biomolecules and biocatalysts, the bacteria from marine extreme ecosystems contribute to increase chances of success. Since 1989, Ifremer has been involved in the discovery and the description of biotechnologically important microorganisms from hydrothermal deep-sea origin and other marine extreme ecosystems. Microorganisms have been recovered from samples collected all over the world. Screenings performed on these samples led to the discovery of several polysaccharide-producing bacteria. Up to now, more than 15 bacterial strains, belonging to four main marine genera, have been described to produce exopolysaccharides (EPS) with both unusual structural features and innovative properties. These EPS present original structure that can be modified to design compounds and improve their specificity. Different processes have been developed to perform chemical depolymerisation and substitution (sulphation) of EPS with the purpose to obtain bioactive derivatives possessing glycosaminoglycan-like (GAG-like) biological properties. The low-molecular-weight oversulphated derivatives can act synergistically with specific growth factors to induce the cell differentiation and present a real potential in cell therapy and tissue engineering. The actions of biologically active polysaccharides are largely dependent on their molecular structure, in particular the composition of the repeating unit, molecular size and sulphation degree. The current processes to modify the EPSs, resulting in GAG-like molecules, are performed by chemical methods. But the need for environmentally friendly processes, in particular those derived from the white biotechnology, is important. Enzymes are indeed ideal biocatalysts due to their stereo- and regio-selectivity, and their activity in mild conditions. Enzymes capable of generating targeted modifications are thus looked for (glycoside hydrolases or polysaccharide lyases, carbohydrate sulphotransferases). In this context, the identification and the characterisation of enzymes for the bioprocessing of the bacterial polysaccharides may be carried out by a large screening work of diverse samples. However, these techniques of functional screening are not suitable for certain enzymes such as sulphotransferases because of the high cost of the sulphate donor. With the increasing number of microbial genomes sequenced, numerous enzyme genes related to polysaccharide biosynthesis and biotransformations are identified and molecular mechanisms of the biosynthesis of the polysaccharides are better understood. Future applications will involve traditional and molecular approaches to achieve integrated bioengineering approach for the production of tailor-made polysaccharides suitable for industrial and medical applications.
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