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Biosynthesis and function of extracellular glycans in cyanobacteria.

Kehr JC, Dittmann E - Life (Basel) (2015)

Bottom Line: The complex carbohydrates act as barriers against different types of stress and play a role in intra- as well as inter-species interactions.We discuss similarities with well-studied enterobacterial systems and highlight the unique features of cyanobacteria.We pay special attention to colony formation and EPS biosynthesis in the bloom-forming cyanobacterium, Microcystis aeruginosa.

View Article: PubMed Central - PubMed

Affiliation: University of Potsdam, Institute for Biochemistry and Biology, Department of Microbiology, Karl-Liebknecht-Str. 24/25, 14476 Potsdam-Golm, Germany. jckehr@uni-potsdam.de.

ABSTRACT
The cell surface of cyanobacteria is covered with glycans that confer versatility and adaptability to a multitude of environmental factors. The complex carbohydrates act as barriers against different types of stress and play a role in intra- as well as inter-species interactions. In this review, we summarize the current knowledge of the chemical composition, biosynthesis and biological function of exo- and lipo-polysaccharides from cyanobacteria and give an overview of sugar-binding lectins characterized from cyanobacteria. We discuss similarities with well-studied enterobacterial systems and highlight the unique features of cyanobacteria. We pay special attention to colony formation and EPS biosynthesis in the bloom-forming cyanobacterium, Microcystis aeruginosa.

No MeSH data available.


Related in: MedlinePlus

Genetic organization of EPS gene clusters in E. coli, as well as a representation of the loci harboring homologues of EPS core genes in the complete genome of Microcystis aeruginosa NIES 843 and draft genomes of other Microcystis strains. The typical organization of Group 1 and 4 and Group 2 and 3 capsule biosynthesis clusters is depicted for E. coli (top). Grey boxes highlight the conserved core genes. Genes encoding glycosyltransferases and precursor synthesis vary depending on the serotype. Wzx/Wzy and Wzm/Wzt gene homologues in Microcystis are shown in their genetic background (bottom). Additional genes putatively involved in EPS biosynthesis are shown in dark grey, and genes encoding unrelated functions are shown in light grey. The locus tags of relevant genes are depicted below. Solid black lines indicate similar sequences in Microcystis strains listed on the right end. Dotted lines represent upstream or downstream sequences, which do not show homology to corresponding flanking regions in NIES 843, and no line indicates missing sequence information due to unfinished genome status.
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life-05-00164-f003: Genetic organization of EPS gene clusters in E. coli, as well as a representation of the loci harboring homologues of EPS core genes in the complete genome of Microcystis aeruginosa NIES 843 and draft genomes of other Microcystis strains. The typical organization of Group 1 and 4 and Group 2 and 3 capsule biosynthesis clusters is depicted for E. coli (top). Grey boxes highlight the conserved core genes. Genes encoding glycosyltransferases and precursor synthesis vary depending on the serotype. Wzx/Wzy and Wzm/Wzt gene homologues in Microcystis are shown in their genetic background (bottom). Additional genes putatively involved in EPS biosynthesis are shown in dark grey, and genes encoding unrelated functions are shown in light grey. The locus tags of relevant genes are depicted below. Solid black lines indicate similar sequences in Microcystis strains listed on the right end. Dotted lines represent upstream or downstream sequences, which do not show homology to corresponding flanking regions in NIES 843, and no line indicates missing sequence information due to unfinished genome status.

Mentions: Nevertheless, many cyanobacterial genome sequences were added to the databases in recent years, which offers the opportunity to systematically screen for genes involved in glycan synthesis. We used query sequences for conserved genes, as well as serotype-specific glycosyltransferases from E. coli to identify putative EPS genes in Microcystis aeruginosa NIES 843 (Figure 3). Indeed, the presence of a Wzm/Wzt system could be confirmed with identities of 32% and 41% compared to the E. coli enzymes, although the genes are not embedded in a gene cluster harboring further glycan biosynthesis genes. Putative wzx and wzy genes could be identified, as well, but these showed only partial (~40%) coverage and low (~27%) identity to the E. coli query sequences. However, glycosyltransferases and sugar epimerases were identified in direct or close vicinity, implying that these genes might be involved in the synthesis of exopolysaccharides. In addition, methyltransferases and sulfotransferases were identified, which may facilitate further modifications of the glycans. Furthermore, several glycosyltransferases spread all over the chromosome were found, many of which could not be assigned to EPS synthesis based on their genomic context. Previous studies showed that the sequence identity of Wzx and Wzy orthologues in different microorganisms is very low, and thus, BLAST searches with query sequences from distant species might fail to identify Wzx and Wzy proteins if search parameters are not adjusted properly [34,35]. We also tried to estimate the level of conservation of the putative EPS synthesis loci in other Microcystis genomes [36,37,38,39] by looking for homologues of the conserved pathway enzymes (Figure 3). Apparently, at least one wzm/wzt and wzx/wzy system could be identified in each strain, with some strains possessing multiple wzx/wzy systems. Furthermore, some variations in the genetic neighborhood were observed, although upstream and downstream regions of wzm/t/x/y genes were frequently not assessable due to the unfinished status of most genomes. However, a mosaic-like distribution, rather than a clustered organization, of genes implicated in EPS biosynthesis over the whole chromosome might indicate frequent recombination, which contributes to strain-specific glycan structure diversification.


Biosynthesis and function of extracellular glycans in cyanobacteria.

Kehr JC, Dittmann E - Life (Basel) (2015)

Genetic organization of EPS gene clusters in E. coli, as well as a representation of the loci harboring homologues of EPS core genes in the complete genome of Microcystis aeruginosa NIES 843 and draft genomes of other Microcystis strains. The typical organization of Group 1 and 4 and Group 2 and 3 capsule biosynthesis clusters is depicted for E. coli (top). Grey boxes highlight the conserved core genes. Genes encoding glycosyltransferases and precursor synthesis vary depending on the serotype. Wzx/Wzy and Wzm/Wzt gene homologues in Microcystis are shown in their genetic background (bottom). Additional genes putatively involved in EPS biosynthesis are shown in dark grey, and genes encoding unrelated functions are shown in light grey. The locus tags of relevant genes are depicted below. Solid black lines indicate similar sequences in Microcystis strains listed on the right end. Dotted lines represent upstream or downstream sequences, which do not show homology to corresponding flanking regions in NIES 843, and no line indicates missing sequence information due to unfinished genome status.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390846&req=5

life-05-00164-f003: Genetic organization of EPS gene clusters in E. coli, as well as a representation of the loci harboring homologues of EPS core genes in the complete genome of Microcystis aeruginosa NIES 843 and draft genomes of other Microcystis strains. The typical organization of Group 1 and 4 and Group 2 and 3 capsule biosynthesis clusters is depicted for E. coli (top). Grey boxes highlight the conserved core genes. Genes encoding glycosyltransferases and precursor synthesis vary depending on the serotype. Wzx/Wzy and Wzm/Wzt gene homologues in Microcystis are shown in their genetic background (bottom). Additional genes putatively involved in EPS biosynthesis are shown in dark grey, and genes encoding unrelated functions are shown in light grey. The locus tags of relevant genes are depicted below. Solid black lines indicate similar sequences in Microcystis strains listed on the right end. Dotted lines represent upstream or downstream sequences, which do not show homology to corresponding flanking regions in NIES 843, and no line indicates missing sequence information due to unfinished genome status.
Mentions: Nevertheless, many cyanobacterial genome sequences were added to the databases in recent years, which offers the opportunity to systematically screen for genes involved in glycan synthesis. We used query sequences for conserved genes, as well as serotype-specific glycosyltransferases from E. coli to identify putative EPS genes in Microcystis aeruginosa NIES 843 (Figure 3). Indeed, the presence of a Wzm/Wzt system could be confirmed with identities of 32% and 41% compared to the E. coli enzymes, although the genes are not embedded in a gene cluster harboring further glycan biosynthesis genes. Putative wzx and wzy genes could be identified, as well, but these showed only partial (~40%) coverage and low (~27%) identity to the E. coli query sequences. However, glycosyltransferases and sugar epimerases were identified in direct or close vicinity, implying that these genes might be involved in the synthesis of exopolysaccharides. In addition, methyltransferases and sulfotransferases were identified, which may facilitate further modifications of the glycans. Furthermore, several glycosyltransferases spread all over the chromosome were found, many of which could not be assigned to EPS synthesis based on their genomic context. Previous studies showed that the sequence identity of Wzx and Wzy orthologues in different microorganisms is very low, and thus, BLAST searches with query sequences from distant species might fail to identify Wzx and Wzy proteins if search parameters are not adjusted properly [34,35]. We also tried to estimate the level of conservation of the putative EPS synthesis loci in other Microcystis genomes [36,37,38,39] by looking for homologues of the conserved pathway enzymes (Figure 3). Apparently, at least one wzm/wzt and wzx/wzy system could be identified in each strain, with some strains possessing multiple wzx/wzy systems. Furthermore, some variations in the genetic neighborhood were observed, although upstream and downstream regions of wzm/t/x/y genes were frequently not assessable due to the unfinished status of most genomes. However, a mosaic-like distribution, rather than a clustered organization, of genes implicated in EPS biosynthesis over the whole chromosome might indicate frequent recombination, which contributes to strain-specific glycan structure diversification.

Bottom Line: The complex carbohydrates act as barriers against different types of stress and play a role in intra- as well as inter-species interactions.We discuss similarities with well-studied enterobacterial systems and highlight the unique features of cyanobacteria.We pay special attention to colony formation and EPS biosynthesis in the bloom-forming cyanobacterium, Microcystis aeruginosa.

View Article: PubMed Central - PubMed

Affiliation: University of Potsdam, Institute for Biochemistry and Biology, Department of Microbiology, Karl-Liebknecht-Str. 24/25, 14476 Potsdam-Golm, Germany. jckehr@uni-potsdam.de.

ABSTRACT
The cell surface of cyanobacteria is covered with glycans that confer versatility and adaptability to a multitude of environmental factors. The complex carbohydrates act as barriers against different types of stress and play a role in intra- as well as inter-species interactions. In this review, we summarize the current knowledge of the chemical composition, biosynthesis and biological function of exo- and lipo-polysaccharides from cyanobacteria and give an overview of sugar-binding lectins characterized from cyanobacteria. We discuss similarities with well-studied enterobacterial systems and highlight the unique features of cyanobacteria. We pay special attention to colony formation and EPS biosynthesis in the bloom-forming cyanobacterium, Microcystis aeruginosa.

No MeSH data available.


Related in: MedlinePlus