Microbial alginate

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. 

A strain of Azotobacter vinelandii was cultured in a 15 m3 stirred fermenter for the production of alginate. Under current conditions the mass transfer coefficient, kLa, is 0.18 s. Oxygen solubility in the fermentation broth is approximately 8 X 10 3 kgm-3.9 The specific oxygen uptake rate is 12.5 mmol g 1 h. What is the maximum cell density in the broth If copper sulphate is accidentally added to the fermentation broth, which may reduce the oxygen uptake rate to 3 mmol g 1 h 1 and inhibit the microbial cell growth, what would be the maximum cell density in this condition ... 

Guo, X.-L., Deng, G., Xu, J. and Wang, M.-X. (2006) Immobilization of Rhodococcus sp. AJ270 in alginate capsules and its application in enantioselective biotransformation of ira/i.s-2-methyl-3- phenyl-oxiranecarbonitrile and amide. Enzyme and Microbial Technology, 39, 1-5. 

Lebeau et al. (2002) investigated the sorption of cadmium by viable microbial cells that were free or immobilized in alginate beads by incubating the bacteria in a liquid soil extract medium at pH 5 7 and Cd concentrations of 1 to 10 mg L-1. The percentage of Cd biosorbed reached a maximum (69%) at low Cd concentrations and neutral pH. Thus, the effectiveness of bacteria, inoculated into metal-contaminated soils, would largely depend on the concentration of the metal and its distribution between the biomass and the medium. 

Adsorption of azo dyes by the biomass is considered as the first step of their biological reduction [39]. Because of adsorption, the dye is concentrated onto the biomass until its saturation the amount of adsorbed dye is then proportional to the amount of biomass [4CM-2]. Steffan et al. [43] observed that 68% Ethyl Orange was rapidly adsorbed on a microbial consortium immobilized in alginate beads, but only after the addition of glucose or starch the dye was effectively degraded. 

Steffan S, Bardi L, Marzona M (2005) Azo dyes biodegradation by microbial cultures immobilized in alginate beads. Environ Int Special Issue Recent Adv Bioremediat 31 (2) 201-205... 

Roy, I. and Gupta, M.N., Hydrolysis of starch by a mixture of glucoamylase and pullulanase entrapped individually in calcium alginate beads, Enzyme Microbial Tech., 34 (2004) 26-32. 

K Nakamura, Y Kawai, S Oka, A Ohno. A new method for stereochemical control of microbial reduction. Reduction of (3-keto esters with baker s yeast immobilized by magnesium alginate. Tetrahedron Lett 2245-2246, 1989. 

The Microbial Production of Alginates, Tate and Lyle Ltd., Reading, England, 1975. 

Addition of microorganisms and enzymes stimulates the biodegradation of xenobiotics in soils. Most efforts have been directed toward the use of bacterial inocula grown in large fermenters for the bioremediation of soils contaminated with PCP. Also, microbial immobilization on bark chips or their encapsulation in polyurethane or alginate, enhances their PCP-degrading ability as well as their resistance to PCP toxicity. 

Alginic acid dispersions are susceptible to microbial spoilage on storage, which may result in some depolymerization and hence a decrease in viscosity. Dispersions should therefore be preserved with an antimicrobial preservative such as benzoic acid potassium sorbate sodium benzoate sorbic acid or paraben. Concentrations of 0.1-0.2% are usually used. 

In the solid state, potassium alginate is a stable material that is not prone to microbial spoilage. Over time, a slow reduction in the degree of polymerization can occur, which may be reflected in a reduction in the viscosity of solutions. As both temperature and moisture can impair the performance of potassium alginate, storage below 25°C is recommended. 

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