Production of Microbial Polysaccharides

Searching existing culture collections is frequently quicker, cheaper, and easier than isolation from Nature. Two guides to collections of industrially useful microbes have been published.203,204 

Microbial, Exocellular Polysaccharides Containing Acidic Sugar Residues 

Micro-organism CIcA ManA Other Gal GIc Man Other acetal groups References 

Bacterial, Exocellular Polysaccharides Containing Neutral Sugar Residues 

Corynebacterium insidiosum Corynebacterium sepedonicum Rhizobium meliloti Rhizobium japonicum 

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At present, the discovery of new polysaccharides relies on screening of the extracellular polysaccharides produced by microorganisms. Fungi and yeasts are also potential sources of new polysaccharides. The production of microbial polysaccharide has the advantages of controlled cost, abundant supply and ease of modification of the chemical structure. These new polysaccharides with new properties may generate new market opportunities. Microbial polysaccharides can be classified as extracellular structural or intercellular storage forms. Extracellular polysaccharide can be either exocellular capsules of the cell wall or loose slime components that accumulate outside the cell wall and then diffuse into the medium. 

It is sometimes claimed that mucilage and similar gels may help to maintain hydraulic conductivity between root and. soil (52). However, the hydraulic conductivity of soils is often substantially decreased when soils are irrigated with waste water. Apart from the inducement of sodicity, which is real in many cases, the decreases in hydraulic conductivity are attributed largely to the production of microbial biomass, particularly extracellular polysaccharides (e.g.. Ref. 53). These extracellular polysaccharides form gels that may store large quantities of water and allow water and ions to diffu.se through them at rates not much less than those of free water, but they could be expected to restrict mass flow of water and thus nutrients, to roots (54). 

As with higher organisms, a common feature of bacteria is the production of extracellular polysaccharides, during growth. Within the last 20 years, the large-scale production of microbial biopolymers has become feasible, and mainly two microbial products, i.e., xanthan and dextran are widely used in the pharmaceutical industry today. 

Toksoy Oner E. Microbial production of extracellular polysaccharides from biomass. In Feng Z, editor. 

Personal Care Products Council. Concentration of use by FDA product category microbial polysaccharides 2011.10 pages. 

Xanthan Gum. As a result of a project to transform agriculturally derived products into industrially usefiil products by microbial action, the Northern Regional Research Laboratories of the USDA showed that the bacterium TCanthomonas campestris - noduces a polysaccharide with industrially usefiil properties (77). Extensive research was carried out on this interesting polysaccharide in several industrial laboratories during the eady 1960s, culminating in commercial production in 1964. 

Xanthan gum [11138-66-2] is an anionic heteropolysaccharide produced by several species of bacteria in the genus Aanthomonas A. campestris NRRL B-1459 produces the biopolymer with the most desirable physical properties and is used for commercial production of xanthan gum (see Gums). This strain was identified in the 1950s as part of a program to develop microbial polysaccharides derived from fermentations utilizing com sugar (333,334). The primary... 

Polarimetric determination of the sucrose concentration of a solution is vaUd when sucrose is the only optically active constituent of the sample. In practice, sugar solutions are almost never pure, but contain other optically active substances, most notably the products of sucrose inversion, fmctose and glucose, and sometimes also the microbial polysaccharide dextran, which is dextrorotatory. Corrections can be made for the presence of impurities, such as invert, moisture, and ash. The advantage of polarization is that it is rapid, easy, and very reproducible, having a precision of 0.001°. 

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. 

Dextran is the first microbial polysaccharide produced and utilized on an industrial scale. The potential importance of dextran as a structually (and property) controlled feedstock is clearly seen in light of the recent emphasis of molecular biologists and molecular engineers in the generation of microbes for feedstock production. Dextran is employed as pharmaceuticals (additives and coatings of medications), within cosmetics, as food extenders, as water-loss inhibitors in oilwell drilling muds and as the basis for a number of synthetic resins. 

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