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Challenges and perspectives in combinatorial assembly of novel exopolysaccharide biosynthesis pathways.

Becker A - Front Microbiol (2015)

Bottom Line: However, previous manipulations primarily focused on increasing polysaccharide yield, with structural modifications restricted to removal of side chains or non-sugar decorations.This article outlines the biosynthetic pathways of the bacterial heteroexopolysaccharides xanthan and succinoglycan, which are used as thickening and stabilizing agents in food and non-food industries.Challenges and perspectives of combining synthetic biology approaches with directed evolution to overcome obstacles in assembly of novel EPS biosynthesis pathways are discussed.

View Article: PubMed Central - PubMed

Affiliation: LOEWE Center for Synthetic Microbiology and Faculty of Biology, Philipps-University of Marburg , Marburg, Germany.

ABSTRACT
Because of their rheological properties various microbial polysaccharides are applied as thickeners and viscosifiers both in food and non-food industries. A broad variety of microorganisms secrete structurally diverse exopolysaccharides (EPS) that contribute to their surface attachment, protection against abiotic or biotic stress factors, and nutrient gathering. Theoretically, a massive number of EPS structures are possible through variations in monosaccharide sequences, condensation linkages and non-sugar decorations. Given the already-high diversity of EPS structures, taken together with the principal of combinatorial biosynthetic pathways, microbial polysaccharides are an attractive class of macromolecules with which to generate novel structures via synthetic biology approaches. However, previous manipulations primarily focused on increasing polysaccharide yield, with structural modifications restricted to removal of side chains or non-sugar decorations. This article outlines the biosynthetic pathways of the bacterial heteroexopolysaccharides xanthan and succinoglycan, which are used as thickening and stabilizing agents in food and non-food industries. Challenges and perspectives of combining synthetic biology approaches with directed evolution to overcome obstacles in assembly of novel EPS biosynthesis pathways are discussed.

No MeSH data available.


Related in: MedlinePlus

Biosynthetic pathways of xanthan in X. campestris (A) and succinoglycan in S. meliloti (B). Repeat units are synthesized on a C55-undecaprenol phosphate lipid carrier at the inner face of the cytoplasmic membrane. Polymerization occurs by transfer of the lipid carrier-bound growing chain to a monomeric lipid carrier-bound repeat unit in the periplasm at the outer face of the cytoplasmic membrane. Modifications may occur during synthesis of the repeat unit before completion of the oligosaccharide. E.g., acetylated intermediates were detected in succinoglycan biosynthesis (Reuber and Walker, 1993). Ac, acetyl group; Ac-CoA, Acetyl-CoA; Gal, galactosyl group; Glc, glucosyl group; GlcA, glucuronyl group; Man, mannosyl group; PEP, phosphoenolpyruvate; Suc, succinyl group; Suc-CoA, succinyl-CoA.
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Figure 2: Biosynthetic pathways of xanthan in X. campestris (A) and succinoglycan in S. meliloti (B). Repeat units are synthesized on a C55-undecaprenol phosphate lipid carrier at the inner face of the cytoplasmic membrane. Polymerization occurs by transfer of the lipid carrier-bound growing chain to a monomeric lipid carrier-bound repeat unit in the periplasm at the outer face of the cytoplasmic membrane. Modifications may occur during synthesis of the repeat unit before completion of the oligosaccharide. E.g., acetylated intermediates were detected in succinoglycan biosynthesis (Reuber and Walker, 1993). Ac, acetyl group; Ac-CoA, Acetyl-CoA; Gal, galactosyl group; Glc, glucosyl group; GlcA, glucuronyl group; Man, mannosyl group; PEP, phosphoenolpyruvate; Suc, succinyl group; Suc-CoA, succinyl-CoA.

Mentions: Typically, genes directing synthesis, polymerization and export of a specific polysaccharide are clustered in the bacterial genome. In contrast, genes involved in the synthesis of common nucleotide sugar precursors required for the production of more than one oligo- or polysaccharide are frequently uncoupled from the specific biosynthesis gene clusters (Harding et al., 1993). However, many clusters contain additional copies of these genes or genes for the synthesis of nucleotide sugar precursors specific to the polysaccharide. In X. campestris and S. meliloti, the 16 kb gum and the 24 kb exo gene cluster, respectively, encode glycosyltransferases, enzymes catalyzing the addition of non-sugar decorations, and proteins involved in the terminal steps of xanthan and succinoglycan biosynthesis (Becker and Pühler, 1998; Becker et al., 1998; Figure 2). While in the succinoglycan biosynthesis gene cluster, exoB and exoN encode a UDP glucose 4-epimerase and a UDP-glucose pyrophosphorylase, respectively, the xanthan biosynthesis gene region does not encode enzymes involved in synthesis of nucleotide sugar precursors.


Challenges and perspectives in combinatorial assembly of novel exopolysaccharide biosynthesis pathways.

Becker A - Front Microbiol (2015)

Biosynthetic pathways of xanthan in X. campestris (A) and succinoglycan in S. meliloti (B). Repeat units are synthesized on a C55-undecaprenol phosphate lipid carrier at the inner face of the cytoplasmic membrane. Polymerization occurs by transfer of the lipid carrier-bound growing chain to a monomeric lipid carrier-bound repeat unit in the periplasm at the outer face of the cytoplasmic membrane. Modifications may occur during synthesis of the repeat unit before completion of the oligosaccharide. E.g., acetylated intermediates were detected in succinoglycan biosynthesis (Reuber and Walker, 1993). Ac, acetyl group; Ac-CoA, Acetyl-CoA; Gal, galactosyl group; Glc, glucosyl group; GlcA, glucuronyl group; Man, mannosyl group; PEP, phosphoenolpyruvate; Suc, succinyl group; Suc-CoA, succinyl-CoA.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4496566&req=5

Figure 2: Biosynthetic pathways of xanthan in X. campestris (A) and succinoglycan in S. meliloti (B). Repeat units are synthesized on a C55-undecaprenol phosphate lipid carrier at the inner face of the cytoplasmic membrane. Polymerization occurs by transfer of the lipid carrier-bound growing chain to a monomeric lipid carrier-bound repeat unit in the periplasm at the outer face of the cytoplasmic membrane. Modifications may occur during synthesis of the repeat unit before completion of the oligosaccharide. E.g., acetylated intermediates were detected in succinoglycan biosynthesis (Reuber and Walker, 1993). Ac, acetyl group; Ac-CoA, Acetyl-CoA; Gal, galactosyl group; Glc, glucosyl group; GlcA, glucuronyl group; Man, mannosyl group; PEP, phosphoenolpyruvate; Suc, succinyl group; Suc-CoA, succinyl-CoA.
Mentions: Typically, genes directing synthesis, polymerization and export of a specific polysaccharide are clustered in the bacterial genome. In contrast, genes involved in the synthesis of common nucleotide sugar precursors required for the production of more than one oligo- or polysaccharide are frequently uncoupled from the specific biosynthesis gene clusters (Harding et al., 1993). However, many clusters contain additional copies of these genes or genes for the synthesis of nucleotide sugar precursors specific to the polysaccharide. In X. campestris and S. meliloti, the 16 kb gum and the 24 kb exo gene cluster, respectively, encode glycosyltransferases, enzymes catalyzing the addition of non-sugar decorations, and proteins involved in the terminal steps of xanthan and succinoglycan biosynthesis (Becker and Pühler, 1998; Becker et al., 1998; Figure 2). While in the succinoglycan biosynthesis gene cluster, exoB and exoN encode a UDP glucose 4-epimerase and a UDP-glucose pyrophosphorylase, respectively, the xanthan biosynthesis gene region does not encode enzymes involved in synthesis of nucleotide sugar precursors.

Bottom Line: However, previous manipulations primarily focused on increasing polysaccharide yield, with structural modifications restricted to removal of side chains or non-sugar decorations.This article outlines the biosynthetic pathways of the bacterial heteroexopolysaccharides xanthan and succinoglycan, which are used as thickening and stabilizing agents in food and non-food industries.Challenges and perspectives of combining synthetic biology approaches with directed evolution to overcome obstacles in assembly of novel EPS biosynthesis pathways are discussed.

View Article: PubMed Central - PubMed

Affiliation: LOEWE Center for Synthetic Microbiology and Faculty of Biology, Philipps-University of Marburg , Marburg, Germany.

ABSTRACT
Because of their rheological properties various microbial polysaccharides are applied as thickeners and viscosifiers both in food and non-food industries. A broad variety of microorganisms secrete structurally diverse exopolysaccharides (EPS) that contribute to their surface attachment, protection against abiotic or biotic stress factors, and nutrient gathering. Theoretically, a massive number of EPS structures are possible through variations in monosaccharide sequences, condensation linkages and non-sugar decorations. Given the already-high diversity of EPS structures, taken together with the principal of combinatorial biosynthetic pathways, microbial polysaccharides are an attractive class of macromolecules with which to generate novel structures via synthetic biology approaches. However, previous manipulations primarily focused on increasing polysaccharide yield, with structural modifications restricted to removal of side chains or non-sugar decorations. This article outlines the biosynthetic pathways of the bacterial heteroexopolysaccharides xanthan and succinoglycan, which are used as thickening and stabilizing agents in food and non-food industries. Challenges and perspectives of combining synthetic biology approaches with directed evolution to overcome obstacles in assembly of novel EPS biosynthesis pathways are discussed.

No MeSH data available.


Related in: MedlinePlus