Microbial exocellular

Microbial, Exocellular Polysaccharides Containing Acidic Sugar Residues... 

Hot water-extractable C accounts for 1-5% of soil organic C (Leinweber et al. 1995 Sparling et al. 1998 Chan and Heenan 1999) and about 50% of this is thought to be present as carbohydrate (Haynes 2005). Because it is usually extracted from air-dried soils much of the pool originates from desiccated microbial cells but it also includes exocellular polysaccharides, root exudates, lysates and humic material (Redl et al. 1990 Leinweber et al. 1995 Sparling et al. 1998). Both hot water extractable C (Sparling et al. 1998 Chan and Heenan 1999) and hot water-extractable carbohydrate (Ball et al. 1996 Haynes and Beare 1997 Debrosz et al. 2002) have been used as indices of soil quality. 

Xanthan is the extracellular (exocellular) polysaccharide produced by Xanthomonas campestris. As with other microbial polysaccharides, the characteristics (polymer structure, molecular weight, solution properties) of xanthan preparations are constant and reproducible when a particular strain of the organism is grown under specified conditions, as is done commercially. The characteristics vary, however, with variations in the strain of the organism, the sources of nitrogen and carbon, degree of medium oxygenation, temperature, pH, and concentrations of various mineral elements. 

Sandford, P. A. (1979). Exocellular microbial polysaccharides. Adv. Carbohydr. Chem. Biochem. 36 265-313. 

Solubility of Exocellular Nickel Complexes in the Soil. To evaluate the effect of microbial metabolites on Ni solubility in soil, the soluble exocellular solution, separated after growth of the 20 selected bacterial isolates and all fungal isolates, was eluted through a column of soil. The concentrations and forms of Ni in the eluates were compared to the concentrations and forms of Ni in water and in the growth medium before and after microbial growth. A column (0.8 x 4 cm) was packed (1.5 g/cc) with sieved (<2 mm), air-dry Ritzville silt loam (1.0 g) and an aliquot of the filtered (<0.4 M<) exocellular medium (2 ml) was eluted through the soil. After 1 ml of eluant was collected, the Ni concentration was determined from the concentration of radio-tracer. Metal form was characterized in soil eluates by TLC and TLE as previously described. 

Modification of Nickel Form by Soil Microbial Isolates. Following isolation from soil and in conjunction with taxonomic characterization, pure cultures of bacteria and fungi were grown to stationary phase in the presence of Ni at several concentration levels. The exocellular solution from each culture was separated by filtration (<0.4 and <0.01 jl) and the Ni-associated components characterized using TLC and TLE. 

Sandford, P. A., "Exocellular microbial polysaccharides". In Advances in Carbohydrate Chemistry and Biochemistry, Vol. Tipson, R. S. and Horton, D., Eds., Academic... 

Sandford P.A. "Exocellular, Microbial Polysaccharides" Adv. Carb. Chem. Biochem., 1979, 36, 297. 

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. 

Stams AIM, de Bok FAM, Plugge CM, van Eekert MHA, Dolling J, Schraa G. Exocellular electron transfer in anaerobic microbial communities. Environ Microbiol 2006 8 371-382. 

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