Marine versus Non-Marine Bacterial Exopolysaccharides and Their Skincare Applications

Exopolysaccharide production by salt-tolerant bacteria: Recent advances, current challenges, and future prospects

Natural biopolymers derived from exopolysaccharides (EPSs) are considered eco-friendly and sustainable alternatives to available traditional synthetic counterparts. Salt-tolerant bacteria inhabiting harsh ecological niches have evolved a number of unique adaptation strategies allowing them to maintain cellular integrity and assuring their long-term survival; among these, producing EPSs can be adopted as an effective strategy to thrive under high-salt conditions. A great diversity of EPSs from salt-tolerant bacteria have attracted widespread attention recently. Because of factors such as their unique structural, physicochemical, and functional characteristics, EPSs are commercially valuable for the global market and their application potential in various sectors is promising. However, large-scale production and industrial development of these biopolymers are hindered by their low yields and high costs. Consequently, the research progress and future prospects of salt-tolerant bacterial EPSs must be systematically reviewed to further promote their application and commercialization. In this review, the structure and properties of EPSs produced by a variety of salt-tolerant bacterial strains isolated from different sources are summarized. Further, feasible strategies for solving production bottlenecks are discussed, which provides a scientific basis and direct reference for more scientific and rational EPS development.

Multi-step semi-synthesis, structural characterization and growth factor interaction study of regiochemically sulfated diabolican polysaccharides

Diabolican is an exopolysaccharide (EPS) produced by Vibrio diabolicus HE800, a mesophilic bacterium firstly isolated from a deep-sea hydrothermal field. Its glycosaminoglycan (GAG)-like structure, consisting of a tetrasaccharide repeating unit composed of two aminosugars (N-acetyl-glucosamine and N-acetyl-galactosamine) and two glucuronic acid units, suggested to subject it to regioselective sulfation processes, in order to obtain some sulfated derivatives potentially acting as GAG mimics. To this aim, a multi-step semi-synthetic approach, relying upon tailored sequence of regioselective protection, sulfation and deprotection steps, was employed in this work. The chemical structure of the obtained sulfated diabolican derivatives was characterized by a multi-technique analytic approach, in order to define both degree of sulfation (DS) and sulfation pattern within the polysaccharide repeating unit, above all. Finally, binding affinity for some growth factors relevant for biomedical applications was measured for both starting diabolican and sulfated derivatives thereof. Collected data suggested that sulfation pattern could be a key structural element for the selective interaction with signaling proteins not only in the case of native GAGs, as already known, but also for GAG-like structures obtained by regioselective sulfation of naturally unsulfated polysaccharides.

Exploring the Exopolysaccharide Production Potential of Bacterial Strains Isolated from Tunisian Blue Crab Portunus segnis Microbiota

The blue crab (BC) Portunus segnis is considered an invasive species colonizing Tunisian coasts since 2014. This work aims to explore its associated bacteria potential to produce anionic exopolysaccharides (EPSs) in order to open up new ways of valorization. In this study, different BC samples were collected from the coastal area of Sfax, Tunisia. First, bacterial DNA was extracted from seven different fractions (flesh, gills, viscera, carapace scraping water, and three wastewaters from the production plant) and then sequenced using the metabarcoding approach targeting the V3-V4 region of the 16S rDNA to describe their microbiota composition. Metabarcoding data showed that the dominant bacterial genera were mainly Psychrobacter, Vagococcus, and Vibrio. In parallel, plate counting assays were performed on different culture media, and about 250 bacterial strains were isolated and identified by sequencing the 16S rDNA. EPS production by this new bacterial diversity was assessed to identify new compounds of biotechnological interest. The identification of the bacterial strains in the collection confirmed the dominance of Psychrobacter spp. strains. Among them, 43 were identified as EPS producers, as revealed by Stains-all dye in agarose gel electrophoresis. A Buttiauxella strain produced an EPS rich in both neutral sugars including rare sugars such as rhamnose and fucose and uronic acids. This original composition allows us to assume its potential for biotechnological applications and, more particularly, for developing innovative therapeutics. This study highlights bacterial strains associated with BC; they are a new untapped source for discovering innovative bioactive compounds for health and cosmetic applications, such as anionic EPS.