Exopolysaccharide biosynthesis

Using the word list below fill in the blanks in the following paragraph concerning exopolysaccharide biosynthesis. 

Keating, D.H. Sinorhizobium meliloti SyrA mediates the transcriptional regulation of genes involved in lipopolysaccharide sulfation and exopolysaccharide biosynthesis. J Bacteriol 189... 

The exact mechanisms involved in further elongation of the chain and in the release of the exopolysaccharides are still unknown, but it is suspected that the site of exopolysaccharide biosynthesis lies in the cytoplasmic membrane,235 where lipopolysaccharide is known to be synthesized. 

Tang, Y.-J. and Zhong, J.-J. Exopolysaccharide biosynthesis and related enzyme activities of the medicinal fungus, Ganoderma lucidum, grown on lactose in a bioreactor. Biotechnol Lett, 24, 1023, 2002. 

Boels, I. C., Ramos, A., Kleerebezem, M., De Vos, W. M. (2001). Functional analysis of the Lactococcus lactis galU and galE genes and their impact on sugar nucleotide and exopolysaccharide biosynthesis. Applied and Environmental Microbiology, 67, 3033—3040. 

Rufling AM, Chen RR. Transcriptome profiling of a curdlan producing Agrobacterium reveals conserved regulatory mechanisms of exopolysaccharide biosynthesis. Microb Cell Factories 2012 11 17. 

Hidalgo-Cantabrana C, Sanchez B, Milani C,Ventura M, MargoUes A, Ruas-Madiedo P. Exopolysaccharide biosynthesis in Bifidobacterium spp. biological functions and a genomic overview. Appl Environ Microbiol 2014 S0 9- S. 

Schematic representation of gene cluster involve in microbial exopolysaccharide biosynthesis, (a) gum gene cluster responsible for xanthan biosynthesis in Xanthomonas campestris and (b) eps gene cluster involve in EPS biosynthesis in Streptococcus thermophilus Sfi6...

Metabolites whose biosynthesis is energy requiring, for example exopolysaccharides using certain substrates. Here, part of the substrate has to be oxidised to provide ATP for biosynthesis and thus the P/O quotient of the producing organism influences the theoretical yield. 

The requirement for oxygen and carbon source for cell biosynthesis are calculated using nitrogen-limited mass balance equations for growth during exopolysaccharide production 01 res (nitrogen-limited cultures). These balances are derived from experimentally determined values of ... 

Figure 7.10 Simplified scheme for the biosynthesis of xanthan. Adapted from Exopolysaccharides in Plant Bacterial Interactions. J A Leight and D L Coplin. Annu Rev Microbial 1992 46 pp 307-46 (see text).

Whereas Escherichia coli O 111 B4 contains only one, cytoplasmi-cally located, CMP-KDO synthetase activity, E. coli LP 1092 appears to contain two, chromatographically distinct, CMP-KDO synthetase activities. One of these is chromatographically similar to the enzyme from E. coli O 111 B4, whereas the other can be eluted from DEAE-cellulose at significantly lower salt concentration.85 The function, if any, of the additional CMP-KDO-synthetase activity is unknown. It has been suggested85 that the enzyme plays a role in the biosynthesis of the KDO-containing exopolysaccharide from E. coli LP 1092. 

In the biosynthesis of the capsular polysaccharide from Xanthomonas campestris, the modification was shown265 to occur at the level of a polyprenyl pentasaccharide diphosphate intermediate prior to polymerization of the repeating units, and enolpyruvate phosphate was a precursor of the pyruvic acid residues. A similar observation was made during a study of the biosynthesis of Rhizobium meliloti exopolysaccharide.266... 

It therefore seems possible that the biosynthesis of plant gums and mucilages follows a mechanism similar to that of bacterial exopolysaccharides. Experimental evidence should be obtained for plant systems in order to test this hypothesis. 

Most microbial exopolysaccharides are apparently synthesized in-tracellularly. However, with various Leuconostoc, Streptococcus, and Bacillus species, such exopolysaccharides as dextran and levan can be formed by adding proper substrates that do not penetrate the cell membrane.216,217 Surprisingly little information is available about the biosynthesis of biopolymers of commercial value. However, as most of them are probably formed intracellularly, the process by which substrates enter microbial cells, where they are modified by various enzymic reactions and finally excreted in polymerized form into the medium, bears attention. Even with a lack of complete biosynthetic information, the results of research on related micro-organisms may be extrapolated to form a reasonable hypothesis for the biosynthesis of polysaccharides. 

Several fundamental features of polysaccharide biosynthesis are apparently present in all microbes. However, the fate of a substrate supplied to an exopolysaccharide-producing, microbial cell depends on the microbial species chosen. Although studies have been made with... 

Figure 1. Transcriptionally regulated network of exopolysaccharide galactoglucan biosynthesis in the Gram-negative soil bacterium S. meliloti that is affected by extracellular phosphate concentration and bacterial population density (AHL, N-acyl homoserine lactone HL, homoserine lactone).

Riiberg, S., Piihler, A. and Becker, A. (1999) Biosynthesis of the exopolysaccharide galactoglucan in Sinorhizobium meliloti is subject to a complex control by the phosphate-dependent regulator PhoB and the proteins ExpG andMucR. Microbiology 145, 603-611. 

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