title: HesF, an exoprotein required for filament adhesion and aggregation in Anabaena sp. PCC 7120.
abstract: Here, we report on the identification and characterization of a protein (Alr0267) named HesF, found in the extracellular milieu of Anabaena sp. PCC 7120 grown diazotrophically. hesF was found to be highly upregulated upon transition from non-nitrogen-fixing to nitrogen-fixing conditions, and the highest transcript levels were detected towards the end of the heterocyst differentiation process. The hesF promoter drives transcription of the gene in heterocysts only, and both NtcA and HetR are essential for the gene's in vivo activation. An examination of HesF's translocation showed that the secretion system is neither heterocyst-specific nor dependent on nitrogen-fixing conditions. Furthermore, HesF was found to be a type I secretion system substrate, since an HgdD mutant failed to secrete HesF. Several analyses revealed that a HesF minus mutant strain lacks the heterocyst-specific polysaccharide fibrous layer, accumulates high amounts of polysaccharides in the medium and that HesF is essential for the typical aggregation phenotype in diazotrophic conditions. Thus, we propose that HesF is a carbohydrate-binding exoprotein that plays a role in maintaining the heterocyst cell wall structure. A combination of and possibly interaction between HesF and heterocyst-specific polysaccharides seems to be responsible for filament adhesion and culture aggregation in heterocyst-forming cyanobacteria.
authors.affiliation: IBMC - Institute for Molecular and Cell Biology, University of Porto, R. do Campo Alegre, 823, 4150-180, Porto, Portugal.
authors.forename: Paulo
authors.initials: P
authors.lastname: Oliveira
authors.forename: Filipe
authors.initials: F
authors.lastname: Pinto
authors.forename: Catarina C
authors.initials: CC
authors.lastname: Pacheco
authors.forename: Rita
authors.initials: R
authors.lastname: Mota
authors.forename: Paula
authors.initials: P
authors.lastname: Tamagnini
mesh_terms: D017033:Anabaena / Q000235:genetics / Q000502:physiology*; D001422:Bacterial Adhesion / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D058947:Bacterial Secretion Systems / Q000235:genetics*; D002473:Cell Wall / Q000378:metabolism*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D009586:Nitrogen Fixation / Q000235:genetics; D010641:Phenotype; D011134:Polysaccharides / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D020543:Proteome / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics; D015854:Up-Regulation
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D011134:Polysaccharides; D020543:Proteome; D014157:Transcription Factors