Exocellular polysaccharides from cyanobacteria and their possible applications

Abstract

Cyanobacteria are photoautotrophic prokaryotes which include a large variety of species of widespread occurrence and with diverse morphological, physiological and biochemical properties. Many cyanobacteria are known to be able to synthesise outermost slimy investments and to release polysaccharidic material into the culture medium during cell growth. These released polysaccharides (RPSs), being easily recoverable from the culture medium, are attracting much interest in view of their possible uses in several industrial applications. In this paper, an overview of the current knowledge on both RPS‐producing cyanobacterial strains (including the possible roles of the exopolysaccharides) and chemical characteristics of the cyanobacterial RPSs is given, with particular emphasis on RPS properties and possible industrial applications. On the whole, cyanobacterial RPSs are characterised by a great variety in both number (from two to 10) and type of constitutive monosaccharides (various arrangements of acidic and neutral sugars). Most polymers show an anionic nature due to the presence of uronic acids and/or other charged groups such as pyruvyl or sulfate. Polypeptide moieties as well as acetyl substituents have also sometimes been found, causing additional structural complexity. All the cyanobacterial RPSs so far tested showed a pseudoplastic behaviour, but with marked differences in both viscosity values and shear thinning. In terms of RPS production, the responses of cyanobacteria to changes of culture conditions appear strain‐dependent. RPS productivities shown by some cyanobacteria are well comparable with those reported for other photosynthetic microorganisms proposed for polysaccharide production, but very low in comparison with those of heterotrophic microorganisms. Nevertheless, cyanobacteria may be regarded as a very abundant source of structurally diverse polysaccharides, some of which may possess unique properties for special applications, not fulfilled by the polymers currently available. However, much work has still to be done to bridge the wide gap existing between data on the biology of the RPS‐producer strains and information concerning technological and other useful properties of the cyanobacterial RPS.

Activity of glycosidases from freshwater heterotrophic microorganisms on the degradation of extracellular polysaccharide produced by Anabaena spiroides (Cyanobacteria)

“…The highest glucosidase activity measured with 4-MUF-α-Dglucoside was about 44 nmol l -1 min -1 . This reflects the large glucose percentage in the EPS from A. spiroides, characteristic of Cyanobacteria exudates, (6). Indeed, the putative enzyme presenting the second highest activity was the one that cleaved 4-MUF-α-D-mannopyranoside and 4-MUF-β-D-mannopyranoside linkages (mannose was the second monosaccharide present in higher concentration in the EPS).…”

Macromolecular and chemical features of the excreted extracellular polysaccharides in induced biological soil crusts of different ages

“…The overall level of complexity of the secreted molecules can be considered as an indicator of the good capability of the inoculated cyanobacteria to adapt to the environmental conditions. Indeed, the presence of uronic acids, known to provide an anionic character to the polysaccharidic exudates (De Philippis and Vincenzini, 1998), increases the water absorption properties and the capability to bind soil particles of the EPSs (Decho, 1990;Nichols and Mancuso Nichols, 2008), thus favoring the formation of soil aggregates and the metabolic activities of the cyanobacteria residing in the IBSCs. On the other side, the presence of hydrophobic monosaccharides, such as the deoxysugars fucose and rhamnose, is known to increase the gluing properties of the EPSs, making easier their adhesion to solid substrates such as soil particles (Rossi et al, 2012a).…”

“…pH, available counter-ions, water availability etc.). While harder and more condensed fractions may constitute stable layers surrounding microbial cells (named sheaths or capsules), less condensed and loosely bound fractions, encompassed under the name of slime, may be massively released in the surrounding environment (De Philippis and Vincenzini, 1998;Nielsen and Jahn, 1999).…”

Effects of light intensity on components and topographical structures of extracellular polysaccharides from the cyanobacteria Nostoc sp.

“…In the carbohydrate part of RPS or CPS, glucose and galactose were the most abundant, rhamnose, xylose, mannose, galacturonic acid, and glucuronic acid were present as minor components. Different light regimens did not affect the monosaccharidic composition of EPS (Vincenzini et al, 1993;De Philippis and Vincenzini, 1998). We found that light intensity also did not significantly affect the quality of the polymer described above.…”

“…Several recent studies on the influence of light intensity (Friedman et al, 1991;Moreno et al, 1998;Otero and Vincenzini, 2003;Trabelsi et al, 2009;Yu et al, 2010;Mota et al, 2013) and wavelengths (Ehling-Schulz et al, 1997;Chen et al, 2009) on EPS yield have been reported. Different light regimens (continuous light and light-dark cycles) do not significantly affect the monosaccharidic composition of EPS (Vincenzini et al, 1993;De Philippis and Vincenzini, 1998). However, little information is available about the effects of light intensity on the monosaccharidic composition of EPS.…”