Microbial biopolymers

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. 

The formation of humus in most soils is likely the result of a combination of several processes, which Kogel-Knabner (1993) has summarized as selective preservation of recalcitrant plant and microbial biopolymers, direct transformation and microbial resynthesis (Figure 23). The relative... 

Dextran is a microbial biopolymer [58] whose molecular structure is composed exclusively of monomeric 2-D-glucopyranosil units, linked mainly by (P-1,6) glucosidic bonds (Fig. 13.11). Its applications depend on its molecular mass [59]. Two dextran products are available in most countries for clinical purposes dextran 70, with a molecular mass of about 70 000 and dextran 40 with a molecular mass 40 000. Dextran fractions are readily soluble in water and electrolyte media to form clear, stable solutions significantly insensitive to pH. They are also soluble in some solvents such as methyl sulphide, formamide and ethylene glycol [60]. 

F. Freitas, V.D. Alves, I. Coelhoso, M.A.M. Reis, Production and food apphcations of microbial biopolymers, in J.A. Teixeira and A.A. Vicente, eds.. Engineering Aspects of Food Biotechnology. Parti Use of Biotechnology in the Development of Food Processes and Products, CRC Press/Taylor Francis Croup, US, 2013. 

Sebastian Munoz-Guerra completed his Ph.D in Organic Chemistry in 1974 at the University of Seville. After postdoctoral work on crystal structure and morphology of non-conventional nylons, he initiated research on synthesis and characterization of bio-based polymers and copolymers. Since 1987, he is full Professor in Chemical Engineering at the Technical University of Catalonia in Barcelona. His current research is focussed on the development of polyesters, polyamides and polyurethanes derived from carbohydrates with special attention paid to industrial aromatic polyesters, as well as on modification of microbial biopolymers with therapeutic interest. He has authored more than 200 peer reviewed papers and several book chapters, and has been granted more than 15 patents on these issues. 

Xanthan gum, usually shortened to Xanthan, is another widely used polymer in oil fields. Xanthan is a microbial biopolymer, produced by the fermentation of glucose, sucrose, or lactose by the Xanthomonas campestris bacterium that are present in Xanthan in D-glucose, D-mannose, and D-glucuronic acid, as shown in Figure 3. 

A microbial biopolymer can become a protein look-alike in terms of surface properties if the polysaccharide structure has a large number of hydrophobic side chains attached to the sugar backbone. 

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... 

Biopolymers are the naturally occurring macromolecular materials that are the components of all living systems. There are three principal categories of biopolymers, each of which is the topic of a separate article in the Eniyclopedia proteins (qv) nucleic acids (qv) and polysaccharides (see Carbohydrates Microbial polysaccharides). Biopolymers are formed through condensation of monomeric units ie, the corresponding monomers are amino acids (qv), nucleotides, and monosaccharides, for proteins, nucleic acids, and polysaccharides, respectively. The term biopolymers is also used to describe synthetic polymers prepared from the same or similar monomer units as are the natural molecules. 

A process using a microbially gelled biopolymer was developed and used to modify the permeability in coreflood experiments [128]. Curdlan is a microbial carbohydrate with 1,3-P-linkages. Alkaline-soluble curdlan biopolymer was... 

There are also structural differences between humic substances or UDOM collected from rivers and oceans (Table I). Humic substances and UDOM from rivers are enriched in aromatic components compared with their counterparts from the ocean. Terrestrial vegetation is relatively rich in aromatic components, such as lignins and tannins, and this is reflected in the greater aromatic nature of DOM in rivers. These biopolymers are relatively resistant to microbial degradation and are important components of river DOM. Humic substances and UDOM from the ocean are enriched in carbohydrates compared with their counterparts from rivers. This is consistent with observations of higher C-normalized yields of neutral sugars in bulk DOM from the ocean compared with rivers (Table I). 

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