title: Understanding the physiological roles of polyhydroxybutyrate (PHB) in Rhodospirillum rubrum S1 under aerobic chemoheterotrophic conditions.
abstract: Polyhydroxybutyrate (PHB) is an important biopolymer accumulated by bacteria and associated with cell survival and stress response. Here, we make two surprising findings in the PHB-accumulating species Rhodospirillum rubrum S1. We first show that the presence of PHB promotes the increased assimilation of acetate preferentially into biomass rather than PHB. When R. rubrum is supplied with (13)C-acetate as a PHB precursor, 83.5 % of the carbon in PHB comes from acetate. However, only 15 % of the acetate ends up in PHB with the remainder assimilated as bacterial biomass. The PHB-negative mutant of R. rubrum assimilates 2-fold less acetate into biomass compared to the wild-type strain. Acetate assimilation proceeds via the ethylmalonyl-CoA pathway with (R)-3-hydroxybutyrate as a common intermediate with the PHB pathway. Secondly, we show that R. rubrum cells accumulating PHB have reduced ribulose 1,5-bisphosphate carboxylase (RuBisCO) activity. RuBisCO activity reduces 5-fold over a 36-h period after the onset of PHB. In contrast, a PHB-negative mutant maintains the same level of RuBisCO activity over the growth period. Since RuBisCO controls the redox potential in R. rubrum, PHB likely replaces RuBisCO in this role. R. rubrum is the first bacterium found to express RuBisCO under aerobic chemoheterotrophic conditions.
authors.affiliation: UCD Earth Institute, O'Brien Centre for Science, University College Dublin, Belfield, Dublin 4, Ireland.|School of Biomolecular and Biomedical Science, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Tanja
authors.initials: T
authors.lastname: Narancic
authors.affiliation: UCD Earth Institute, O'Brien Centre for Science, University College Dublin, Belfield, Dublin 4, Ireland.|School of Biomolecular and Biomedical Science, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Elisa
authors.initials: E
authors.lastname: Scollica
authors.affiliation: NovaUCD, Belfield Innovation Park, University College Dublin, Bioplastech Ltd., Belfield, Dublin 4, Ireland.
authors.forename: Shane T
authors.initials: ST
authors.lastname: Kenny
authors.affiliation: Institute of Food and Health and Conway Institute, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Helena
authors.initials: H
authors.lastname: Gibbons
authors.affiliation: Institute of Food and Health and Conway Institute, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Eibhlin
authors.initials: E
authors.lastname: Carr
authors.affiliation: Institute of Food and Health and Conway Institute, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Lorraine
authors.initials: L
authors.lastname: Brennan
authors.affiliation: School of Biomolecular and Biomedical Sciences, Conway, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Gerard
authors.initials: G
authors.lastname: Cagney
authors.affiliation: School of Biomolecular and Biomedical Sciences, Conway, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Kieran
authors.initials: K
authors.lastname: Wynne
authors.affiliation: School of Biomolecular and Biomedical Science, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Cormac
authors.initials: C
authors.lastname: Murphy
authors.affiliation: Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms-Universität, Münster, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Raberg
authors.affiliation: Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms-Universität, Münster, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Heinrich
authors.affiliation: Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms-Universität, Münster, Germany.|Environmental Sciences Department, King Abdulaziz University, Jeddah, Saudi Arabia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Steinbüchel
authors.affiliation: UCD Earth Institute, O'Brien Centre for Science, University College Dublin, Belfield, Dublin 4, Ireland. kevin.oconnor@ucd.ie.|School of Biomolecular and Biomedical Science, University College Dublin, Belfield, Dublin 4, Ireland. kevin.oconnor@ucd.ie.
authors.forename: Kevin E
authors.initials: KE
authors.lastname: O'Connor
mesh_terms: D000085:Acetates / Q000378:metabolism; D000332:Aerobiosis; D002247:Carbon Isotopes / Q000378:metabolism; D006885:Hydroxybutyrates / Q000378:metabolism*; D007553:Isotope Labeling; D064688:Metabolic Flux Analysis; D011091:Polyesters / Q000378:metabolism*; D012247:Rhodospirillum rubrum / Q000378:metabolism / Q000502:physiology*; D000094122:Polyhydroxybutyrates
chemical_list: D000085:Acetates; D002247:Carbon Isotopes; D006885:Hydroxybutyrates; D011091:Polyesters; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates
keywords: Aerobic growth; Crotonyl-CoA carboxylase/reductase; Ethylmalonyl-CoA pathway; Polyhydroxybutyrate (PHB); Rhodospirillum rubrum S1; Ribulose 1,5-bisphosphate carboxylase (RuBisCO)