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Appendages of the cyanobacterial cell.

Schuergers N, Wilde A - Life (Basel) (2015)

Bottom Line: However, only for a very few cyanobacteria structure and function of these appendages have been analyzed.PCC 6803 and analyze the distribution of type IV pili associated genes in other cyanobacteria.Further, we discuss the role of the RNA-chaperone Hfq in pilus function and the presence of genes for the chaperone-usher pathway of pilus assembly in cyanobacteria.

View Article: PubMed Central - PubMed

Affiliation: University of Freiburg, Institute of Biology III, Schänzlestr. 1, 79104 Freiburg, Germany. Nils.Schuergers@biologie.uni-freiburg.de.

ABSTRACT
Extracellular non-flagellar appendages, called pili or fimbriae, are widespread in gram-negative bacteria. They are involved in many different functions, including motility, adhesion, biofilm formation, and uptake of DNA. Sequencing data for a large number of cyanobacterial genomes revealed that most of them contain genes for pili synthesis. However, only for a very few cyanobacteria structure and function of these appendages have been analyzed. Here, we review the structure and function of type IV pili in Synechocystis sp. PCC 6803 and analyze the distribution of type IV pili associated genes in other cyanobacteria. Further, we discuss the role of the RNA-chaperone Hfq in pilus function and the presence of genes for the chaperone-usher pathway of pilus assembly in cyanobacteria.

No MeSH data available.


Related in: MedlinePlus

Synteny of gene clusters encoding all the major components of putative CU pili in different cyanobacteria compared to Synechocystis 6803 where the usher homolog is located elsewhere in the genome. All putative CU pili related cyanobacterial gene clusters exhibiting a conserved domain structure (putative subunits PFAM05229; chaperone PFAM00345; usher PFAM00577) are shown. Weak homology is indicated by broken lines.
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life-05-00700-f002: Synteny of gene clusters encoding all the major components of putative CU pili in different cyanobacteria compared to Synechocystis 6803 where the usher homolog is located elsewhere in the genome. All putative CU pili related cyanobacterial gene clusters exhibiting a conserved domain structure (putative subunits PFAM05229; chaperone PFAM00345; usher PFAM00577) are shown. Weak homology is indicated by broken lines.

Mentions: Yoshimura et al. [69] suggested that two proteins encoded by the genes slr1667 and slr1668 (named construction of cell surface components—cccS and cccP, respectively) are involved in biogenesis of the thick pili in Synechocystis 6803. Immunocytochemical analysis supported the idea that CccS was localized at the cell surface region and CccP in the cell periplasm. Both cccS and cccP mutants are non-motile and have no or less thick pili on their surface as shown by electron microscopy. Interestingly, cccP and cccS transcripts are the most differentially accumulated mRNAs in sycrp1 as well as hfq mutants, which are also non-motile. In their paper Yoshimura et al. [69] proposed a model, where CccS and/or CccP support targeting or stable assembly of the PilQ channel, thereby affecting assembly of thick pili. In addition, they state, that thin pili are not affected, suggesting that CccP and CccS are not involved in assembly of these structures. However, a different hypothesis can be drawn from the analysis of the amino acid sequences of both proteins. CccS exhibits a spore coat protein U-domain (SCPU, PFAM05229), whereas CccP contains a PapD-N domain (PFAM00345) [69]. These domains are typically found in proteins involved in biogenesis of CU pili in gram-negative bacteria via the chaperon/usher pathway. Usually, the respective genes are organized in operons containing at least one subunit of the fimbriae, a chaperone and a membrane protein for translocation of the subunits, the so called usher [18]. During assembly of the CU pili the signal peptide of a fimbriae subunit is cleaved off during its translocation across the cytoplasmic membrane. Further, the chaperone protein assists the correct folding and stabilization of the subunit. After binding to the usher protein, which forms a pore in the outer membrane, the chaperone is displaced and the fimbriae subunit is integrated into a filament on the cell surface [70]. In accordance with the domain structure, CccS might represent a subunit of the CU pilus and CccP the corresponding chaperone. It was already shown that CccS has a signal peptide, which is cleaved off, and that CccS is transported across the outer membrane in a CccP-dependent way [69]. These authors did not link CccSP with assembly of CU pili-like structures on the surface of Synechocystis 6803, most probably because there is no usher homolog encoded in this operon. However, in a phylogenetic analysis Nuccio and Bäumler [18] identified an usher homolog (slr0019, PFAM00577) in Synechocystis 6803. A search in the JGI IMG database (http://img.jgi.doe.gov) for proteins containing usher domains revealed the existence of further slr0019 homologs in different cyanobacteria. Remarkably, in most cases these genes are located directly downstream of a putative cccSP operon and thus represent the classical chaperone/usher operon structure (Figure 2). Thus, it seems plausible that CccSP together with Slr0019 could form CU-like pilus structures defined as the thin pili in Synechocystis 6803 by electron microscopy analysis. Further, their incorrect assembly may affect biogenesis of thick pili, indirectly. This hypothesis is contradictory to the data shown by Yoshimura et al. [69], which suggest that formation of thin pili was not affected in cccS and cccP mutants. However, in this paper it was also mentioned that, whereas bundles of thin-pili-like structures were clearly visualized by negative straining, this was not possible for thin pili. As the subunit composition of these different structures is not known so far, it is hardly possible to conclude from electron microscopy data about the nature of the various pili structures. Clearly, a comprehensive inspection of surface structures, including analysis of an slr0019 mutant, is needed to link putative CU pili related gene products to the respective surface appendages.


Appendages of the cyanobacterial cell.

Schuergers N, Wilde A - Life (Basel) (2015)

Synteny of gene clusters encoding all the major components of putative CU pili in different cyanobacteria compared to Synechocystis 6803 where the usher homolog is located elsewhere in the genome. All putative CU pili related cyanobacterial gene clusters exhibiting a conserved domain structure (putative subunits PFAM05229; chaperone PFAM00345; usher PFAM00577) are shown. Weak homology is indicated by broken lines.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390875&req=5

life-05-00700-f002: Synteny of gene clusters encoding all the major components of putative CU pili in different cyanobacteria compared to Synechocystis 6803 where the usher homolog is located elsewhere in the genome. All putative CU pili related cyanobacterial gene clusters exhibiting a conserved domain structure (putative subunits PFAM05229; chaperone PFAM00345; usher PFAM00577) are shown. Weak homology is indicated by broken lines.
Mentions: Yoshimura et al. [69] suggested that two proteins encoded by the genes slr1667 and slr1668 (named construction of cell surface components—cccS and cccP, respectively) are involved in biogenesis of the thick pili in Synechocystis 6803. Immunocytochemical analysis supported the idea that CccS was localized at the cell surface region and CccP in the cell periplasm. Both cccS and cccP mutants are non-motile and have no or less thick pili on their surface as shown by electron microscopy. Interestingly, cccP and cccS transcripts are the most differentially accumulated mRNAs in sycrp1 as well as hfq mutants, which are also non-motile. In their paper Yoshimura et al. [69] proposed a model, where CccS and/or CccP support targeting or stable assembly of the PilQ channel, thereby affecting assembly of thick pili. In addition, they state, that thin pili are not affected, suggesting that CccP and CccS are not involved in assembly of these structures. However, a different hypothesis can be drawn from the analysis of the amino acid sequences of both proteins. CccS exhibits a spore coat protein U-domain (SCPU, PFAM05229), whereas CccP contains a PapD-N domain (PFAM00345) [69]. These domains are typically found in proteins involved in biogenesis of CU pili in gram-negative bacteria via the chaperon/usher pathway. Usually, the respective genes are organized in operons containing at least one subunit of the fimbriae, a chaperone and a membrane protein for translocation of the subunits, the so called usher [18]. During assembly of the CU pili the signal peptide of a fimbriae subunit is cleaved off during its translocation across the cytoplasmic membrane. Further, the chaperone protein assists the correct folding and stabilization of the subunit. After binding to the usher protein, which forms a pore in the outer membrane, the chaperone is displaced and the fimbriae subunit is integrated into a filament on the cell surface [70]. In accordance with the domain structure, CccS might represent a subunit of the CU pilus and CccP the corresponding chaperone. It was already shown that CccS has a signal peptide, which is cleaved off, and that CccS is transported across the outer membrane in a CccP-dependent way [69]. These authors did not link CccSP with assembly of CU pili-like structures on the surface of Synechocystis 6803, most probably because there is no usher homolog encoded in this operon. However, in a phylogenetic analysis Nuccio and Bäumler [18] identified an usher homolog (slr0019, PFAM00577) in Synechocystis 6803. A search in the JGI IMG database (http://img.jgi.doe.gov) for proteins containing usher domains revealed the existence of further slr0019 homologs in different cyanobacteria. Remarkably, in most cases these genes are located directly downstream of a putative cccSP operon and thus represent the classical chaperone/usher operon structure (Figure 2). Thus, it seems plausible that CccSP together with Slr0019 could form CU-like pilus structures defined as the thin pili in Synechocystis 6803 by electron microscopy analysis. Further, their incorrect assembly may affect biogenesis of thick pili, indirectly. This hypothesis is contradictory to the data shown by Yoshimura et al. [69], which suggest that formation of thin pili was not affected in cccS and cccP mutants. However, in this paper it was also mentioned that, whereas bundles of thin-pili-like structures were clearly visualized by negative straining, this was not possible for thin pili. As the subunit composition of these different structures is not known so far, it is hardly possible to conclude from electron microscopy data about the nature of the various pili structures. Clearly, a comprehensive inspection of surface structures, including analysis of an slr0019 mutant, is needed to link putative CU pili related gene products to the respective surface appendages.

Bottom Line: However, only for a very few cyanobacteria structure and function of these appendages have been analyzed.PCC 6803 and analyze the distribution of type IV pili associated genes in other cyanobacteria.Further, we discuss the role of the RNA-chaperone Hfq in pilus function and the presence of genes for the chaperone-usher pathway of pilus assembly in cyanobacteria.

View Article: PubMed Central - PubMed

Affiliation: University of Freiburg, Institute of Biology III, Schänzlestr. 1, 79104 Freiburg, Germany. Nils.Schuergers@biologie.uni-freiburg.de.

ABSTRACT
Extracellular non-flagellar appendages, called pili or fimbriae, are widespread in gram-negative bacteria. They are involved in many different functions, including motility, adhesion, biofilm formation, and uptake of DNA. Sequencing data for a large number of cyanobacterial genomes revealed that most of them contain genes for pili synthesis. However, only for a very few cyanobacteria structure and function of these appendages have been analyzed. Here, we review the structure and function of type IV pili in Synechocystis sp. PCC 6803 and analyze the distribution of type IV pili associated genes in other cyanobacteria. Further, we discuss the role of the RNA-chaperone Hfq in pilus function and the presence of genes for the chaperone-usher pathway of pilus assembly in cyanobacteria.

No MeSH data available.


Related in: MedlinePlus