title: Heterocyst development and diazotrophic metabolism in terminal respiratory oxidase mutants of the cyanobacterium Anabaena sp. strain PCC 7120.
abstract: Heterocyst development was analyzed in mutants of the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 bearing inactivated cox2 and/or cox3 genes, encoding heterocyst-specific terminal respiratory oxidases. At the morphological level, the cox2 cox3 double mutant (strain CSAV141) was impaired in membrane reorganization involving the so-called honeycomb system that in the wild-type strain is largely or exclusively devoted to respiration, accumulated glycogen granules at conspicuously higher levels than the wild type (in both vegetative cells and heterocysts), and showed a delay in carboxysome degradation upon combined nitrogen deprivation. Consistently, chemical analysis confirmed higher accumulation of glycogen in strain CSAV141 than in the wild type. No impairment was observed in the formation of the glycolipid or polysaccharide layers of the heterocyst envelope, consistent with the chemical detection of heterocyst-specific glycolipids, or in the expression of the heterocyst-specific genes nifHDK and fdxH. However, nitrogenase activity under oxic conditions was impaired in strain CSAV135 (cox3) and undetectable in strain CSAV141 (cox2 cox3). These results show that these dedicated oxidases are required for normal development and performance of the heterocysts and indicate a central role of Cox2 and, especially, of Cox3 in the respiratory activity of the heterocysts, decisively contributing to protection of the N(2) fixation machinery against oxygen. However, in contrast to the case for other diazotrophic bacteria, expression of nif genes in Anabaena seems not to be affected by oxygen.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Centro de Investigaciones Científicas Isla de la Cartuja, Américo Vespucio 49, E-41092 Seville, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Valladares
authors.forename: Iris
authors.initials: I
authors.lastname: Maldener
authors.forename: Alicia M
authors.initials: AM
authors.lastname: Muro-Pastor
authors.forename: Enrique
authors.initials: E
authors.lastname: Flores
authors.forename: Antonia
authors.initials: A
authors.lastname: Herrero
mesh_terms: D017033:Anabaena / Q000201:enzymology* / Q000254:growth & development* / Q000648:ultrastructure; D016667:Bacterial Capsules / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D002462:Cell Membrane / Q000648:ultrastructure; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000648:ultrastructure; D003576:Electron Transport Complex IV / Q000235:genetics / Q000502:physiology*; D006003:Glycogen / Q000032:analysis; D006017:Glycolipids / Q000032:analysis; D002479:Inclusion Bodies / Q000378:metabolism / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D009024:Morphogenesis / Q000502:physiology; D009154:Mutation; D009586:Nitrogen Fixation / Q000502:physiology*; D009591:Nitrogenase / Q000378:metabolism; D010088:Oxidoreductases / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis
chemical_list: D001426:Bacterial Proteins; D006017:Glycolipids; D012333:RNA, Messenger; D006003:Glycogen; D010088:Oxidoreductases; D009591:Nitrogenase; C029130:nitrogenase reductase; D003576:Electron Transport Complex IV