Alginate exopolysaccharide

Commercial applications for polysaccharides include their use as food additives, medicines and industrial products. Although plant polysaccharides (such as starch, agar and alginate) have been exploited commercially for many years, microbial exopolysaccharides have only become widely used over the past few decades. The diversity of polysaccharide structure is far greater in micro-organisms compared to plants and around 20 microbial polysaccharides with market potential have been described. However, microorganisms are still considered to be a rich and as yet underexploited source of exopolysaccharides. 

Davies, D. G., A. M. Chakrabarty, and G. G. Geesey. 1993. Exopolysaccharide production in biofilms substratum activation of alginate gene expression by Pseudomonas aeruginosa. Applied and Environmental Microbiology 59 1181-1186. 

Alginates were first described by Standford in 1881 [1]. They were originally discovered thanks to industrial developments related to iodine production. Alginates are quite widespread in Nature. They can be found as major cell-wall components (up to 45% of the dry matter) in marine brown algae (Phaeophyceae). They also occur in acetylated form as exopolysaccharides produced by bacteria belonging to Pseudomonas and Azotobacter genders. 

The biosynthesis of alginic acid [69, 243, 244] has been investigated in both seaweeds and bacteria. Azotobacter vinelandii produces exopolysaccharide in a high carbon-low nitrogen environment and hexoses, disaccharides and D-mannitol can all provide a carbon source. This bacterium contains enzymes that convert hexose phosphates into GDPMan (reactions A to D and J) which then undergoes oxidation and polymerisation... 

Leid, J. G., Willson, C. J., Shirtliff, M. E., Hassett, D. J., Parsek, M. R., and Jeffers, A. K. (2005). The exopolysaccharide alginate protects Pseudomonas aeruginosa biofilm bacteria from IFN-gamma mediated macrophage killing. J. Immunol. 175, 7512-7518. 

Most studies on microbial exopolysaccharides production have been performed so far using batch fermentation conditions and polymer macromolecules are recovered from fermentation broths by simple chemical and physical techniques, e.g. precipitation and centrifugation. In Scheme 7.2 the route of production of alginate is presented [8]. Some attempts have been made to apply immobilized-cell cultures to the production of alginate and other bacterial polysaccharides. Immobilization techniques are likely to allow the permanent separation of microbial cells from the incubation broth. In the last few years, however, membrane processes have been increasingly used to separate microbial cells from the production medium. A number of studies have therefore focused on the microfiltration of fermentation broths after batch incubation and the mechanisms of membrane fouling by cells, debris, colloidal particles and macromolecules, e.g. for recovery of polysaccharides from fermentation broths [2]. 

Neiss and Cheng have studied the microstructure of alginates and related it to the action of enzymes (69). Baianu and Ozu have examined the gelling mechanism of konjac gum and its interactions with proteins (63). Other studies include bacterial exopolysaccharides (86) and oligosaccharides (83,87),... 

The microbial EPSs are a class of high-value polymers that have many industrial applications. Research in this area has led to the production of several microbial polysaccharides on an industrial scale like xanthan, dextran, alginate, geUan, curdlan. Xanthan and gellan are commercially most appreciated on the global market for hydrocolloids with xanthan gum being the only significant bacterial exopolysaccharide, which accounted for 6% of the total market value. ... 

Fungi and bacteria are sources of polysaccharides and especially of exopolysaccharides which can be produced in culture media on an industrial scale. They are a source of new additives for cosmetic or food applications but also for biological activity. Many of them are now in development a review will be published in the second edition of Reference 12. Many of these polysaccharides are water soluble and able to compete with natural polysaccharides as described before (alginates, carrageenans, galacto- and glucomannans, chitosans, pectins, etc) especially in the domain of food additives. Many books discuss their applications (183-187). 

Microbial Polysaccharides Bacterial polysaccharide bacterial cellulose, dextran, bacterial hyaluronic acid, xanthan, emulsan, p-d glucans, curdlan, alginate, gellan and pullulan, scleroglucan and schizophyllan. bacterial hyaluronic acid, kefiran, exopolysaccharide, xanthan gum, dextran, welan gum, gellan gum, diutan gum and pullulan... 

The exopolysaccharides produced by Pseudomonas aeruginosa and Azoto-bacter vinelandii, differ from those produced by other Gram-negative bacteria, in that the heterosaccharide appears to lack a repeating unit. These polymers consist of mannuronic acid and guluronic acid and closely resemble the alginates produced by marine algae. 

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