Although polysaccharides are ubiquitous and the most abundant renewable bio-components, their studies, covered by the glycochemistry and glycobiology fields, remain a challenge due to their high molecular diversity and complexity. Polysaccharides are industrially used in food products; human therapeutics fall into a more recent research field and pharmaceutical industry is looking for more and more molecules with enhanced activities. Glycosaminoglycans (GAGs) found in animal tissues play a critical role in cellular physiological and pathological processes as they bind many cellular components. Therefore, they present a great potential for the design and preparation of therapeutic drugs. On the other hand, microorganisms producing exopolysaccharides (EPS) are renewable resources meeting well the actual industrial demand. In particular, the diversity of marine microorganisms is still largely unexplored offering great opportunities to discover high value products such as new molecules and biocatalysts. EPS-producing bacteria from the marine environment will be reviewed with a focus on marine-derived EPS from bacteria isolated from deep-sea hydrothermal vents. Information on chemical and structural features, putative pathways of biosynthesis, novel strategies for chemical and enzymatic modifications and potentialities in the biomedical field will be provided. An integrated approach should be used to increase the basic knowledge on these compounds and their applications; new clean environmentally friendly processes for the production of carbohydrate bio-active compounds should also be proposed for a sustainable industry.

The transfer of toxic cyanobacterial Microcystis blooms from freshwater to estuaries constitutes a serious environmental problem worldwide that is expected to expand in scale and intensity with anthropogenic and climate change. The formation and maintenance of Microcystis in colonial form is conditioned to the presence of extracellular polymeric substances (EPS). In this study, we attempted to better understand how the mucilaginous colonial form of Microcystis evolves under environmental stress conditions. In particular, we studied and compared the production and the composition of EPS fractions (attached and free) from natural colonies of a Microcystis bloom and from a unicellular M. aeruginosa strain under salinity and nutrient stress (representing a land‐sea continuum). Our results highlighted a greater production of EPS from the natural colonies of Microcystis than the unicellular one under nutrient and combined stress conditions dominated by the attached form. In comparison to the unicellular Microcystis , EPS produced by the colonial form were characterized by high molecular weight polysaccharides which were enriched in uronic acids and hexosamines, notably for the free fraction in response to increased salinities. This complex extracellular matrix gives the cells the ability to aggregate and allows the colonial cyanobacterial population to cope with osmotic shock.

Bacteria are well-known to synthesize high molecular weight polysaccharides excreted in extracellular domain, which constitute their protective microenvironment. Several bacterial exopolysaccharides (EPS) are commercially available for skincare applications in cosmetic products due to their unique structural features, conferring valuable biological and/or textural properties. This review aims to give an overview of bacterial EPS, an important group of macromolecules used in cosmetics as actives and functional ingredients. For this purpose, the main chemical characteristics of EPS are firstly described, followed by the basics of the development of cosmetic ingredients. Then, a focus on EPS production, including upstream and downstream processes, is provided. The diversity of EPS used in the cosmetic industry, and more specifically of marine-derived EPS is highlighted. Marine bacteria isolated from extreme environments are known to produce EPS. However, their production processes are highly challenging due to high or low temperatures; yield must be improved to reach economically viable ingredients. The biological properties of marine-derived EPS are then reviewed, resulting in the highlight of the challenges in this field.