title: Polyhydroxyalkanoate (PHA) Granules Have no Phospholipids.
abstract: Polyhydroxybutyrate (PHB) granules, also designated as carbonosomes, are supra-molecular complexes in prokaryotes consisting of a PHB polymer core and a surface layer of structural and functional proteins. The presence of suspected phospholipids in the surface layer is based on in vitro data of isolated PHB granules and is often shown in cartoons of the PHB granule structure in reviews on PHB metabolism. However, the in vivo presence of a phospholipid layer has never been demonstrated. We addressed this topic by the expression of fusion proteins of DsRed2EC and other fluorescent proteins with the phospholipid-binding domain (LactC2) of lactadherin in three model organisms. The fusion proteins specifically localized at the cell membrane of Ralstonia eutropha but did not co-localize with PHB granules. The same result was obtained for Pseudomonas putida, a species that accumulates another type of polyhydroxyalkanoate (PHA) granules related to PHB. Notably, DsRed2EC-LactC2 expressed in Magnetospirillum gryphiswaldense was detected at the position of membrane-enclosed magnetosome chains and at the cytoplasmic membrane but not at PHB granules. In conclusion, the carbonosomes of representatives of α-proteobacteria, β-proteobacteria and γ-proteobacteria have no phospholipids in vivo and we postulate that the PHB/PHA granule surface layers in natural producers generally are free of phospholipids and consist of proteins only.
authors.affiliation: Institute of Microbiology, University Stuttgart, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Bresan
authors.affiliation: Institute of Microbiology, University Stuttgart, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Sznajder
authors.affiliation: Department of Organismic Interactions, Eberhard Karls Universität Tübingen, Germany.
authors.forename: Waldemar
authors.initials: W
authors.lastname: Hauf
authors.affiliation: Department of Organismic Interactions, Eberhard Karls Universität Tübingen, Germany.
authors.forename: Karl
authors.initials: K
authors.lastname: Forchhammer
authors.affiliation: Lehrstuhl für Mikrobiologie, Universität Bayreuth, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Pfeiffer
authors.affiliation: Institute of Microbiology, University Stuttgart, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Jendrossek
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000378:metabolism*; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism*; D054813:Polyhydroxyalkanoates / Q000737:chemistry / Q000378:metabolism*
chemical_list: D010743:Phospholipids; D054813:Polyhydroxyalkanoates