title: A second nitrogenase in vegetative cells of a heterocyst-forming cyanobacterium.
abstract: In many filamentous cyanobacteria nitrogen fixation occurs in differentiated cells called heterocysts. Filamentous strains that do not form heterocysts may fix nitrogen in vegetative cells, primarily under anaerobic conditions. We describe here two functional Mo-dependent nitrogenases in a single organism, the cyanobacterium Anabaena variabilis. Using a lacZ reporter with a fluorescent beta-galactoside substrate for in situ localization of gene expression, we have shown that the two clusters of nif genes are expressed independently. One nitrogenase functions only in heterocysts under either aerobic or anaerobic growth conditions, whereas the second nitrogenase functions only under anaerobic conditions in vegetative cells and heterocysts. Differences between the two nif clusters suggest that the nitrogenase that is expressed in heterocysts is developmentally regulated while the other is regulated by environmental factors.
authors.affiliation: Department of Biology, University of Missouri-St. Louis 63121, USA.
authors.forename: T
authors.initials: T
authors.lastname: Thiel
authors.forename: E M
authors.initials: EM
authors.lastname: Lyons
authors.forename: J C
authors.initials: JC
authors.lastname: Erker
authors.forename: A
authors.initials: A
authors.lastname: Ernst
mesh_terms: D000114:Acetylene / Q000378:metabolism; D000595:Amino Acid Sequence; D017033:Anabaena / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D015139:Blotting, Southern; D003001:Cloning, Molecular; D004790:Enzyme Induction; D015870:Gene Expression; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics*; D009591:Nitrogenase / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid; D013559:Symbiosis
chemical_list: D011994:Recombinant Proteins; D009591:Nitrogenase; D000114:Acetylene