title: Dinitrogen fixation is restricted to the terminal heterocysts in the invasive cyanobacterium Cylindrospermopsis raciborskii CS-505.
abstract: The toxin producing nitrogen-fixing heterocystous freshwater cyanobacterium Cylindrospermopsis raciborskii recently radiated from its endemic tropical environment into sub-tropical and temperate regions, a radiation likely to be favored by its ability to fix dinitrogen (diazotrophy). Although most heterocystous cyanobacteria differentiate regularly spaced intercalary heterocysts along their trichomes when combined nitrogen sources are depleted, C. raciborskii differentiates only two terminal heterocysts (one at each trichome end) that can reach >100 vegetative cells each. Here we investigated whether these terminal heterocysts are the exclusive sites for dinitrogen fixation in C. raciborskii. The highest nitrogenase activity and NifH biosynthesis (western-blot) were restricted to the light phase of a 12/12 light/dark cycle. Separation of heterocysts and vegetative cells (sonication and two-phase aqueous polymer partitioning) demonstrated that the terminal heterocysts are the sole sites for nifH expression (RT-PCR) and NifH biosynthesis. The latter finding was verified by the exclusive localization of nitrogenase in the terminal heterocysts of intact trichomes (immunogold-transmission electron microscopy and in situ immunofluorescence-light microscopy). These results suggest that the terminal heterocysts provide the combined nitrogen required by the often long trichomes (>100 vegetative cells). Our data also suggests that the terminal-heterocyst phenotype in C. raciborskii may be explained by the lack of a patL ortholog. These data help identify mechanisms by which C. raciborskii and other terminal heterocyst-forming cyanobacteria successfully inhabit environments depleted in combined nitrogen.
authors: Department of Molecular Genetics and Microbiology, Pontificia Universidad Católica de Chile, Santiago, Chile.
authors: Álvaro M
authors: ÁM
authors: Plominsky
authors: John
authors: J
authors: Larsson
authors: Birgitta
authors: B
authors: Bergman
authors: Nathalie
authors: N
authors: Delherbe
authors: Igor
authors: I
authors: Osses
authors: Mónica
authors: M
authors: Vásquez
mesh_terms: D000458:Cyanobacteria / Q000235:genetics* / Q000378:metabolism*; D046891:Cylindrospermopsis / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008027:Light; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism
chemical_list: D010088:Oxidoreductases; D009591:Nitrogenase; C029130:nitrogenase reductase; D009584:Nitrogen
references: PLoS One. 2010 Feb 16;5(2):e9235
references: 20169071
references: Toxicon. 2004 Oct;44(5):483-9
references: 15450922
references: Mol Cell. 2000 Oct;6(4):961-7
references: 11090634
references: J Cell Sci. 1973 May;12(3):707-23
references: 4198321
references: PLoS Genet. 2007 Dec;3(12):e231
references: 18159947
references: J Bacteriol. 1994 Aug;176(15):4473-82
references: 7913926
references: Curr Protoc Mol Biol. 2001 Nov;Chapter 2:Unit 2.4
references: 18265184
references: Oecologia. 2007 Jun;152(3):473-84
references: 17375336
references: Bioinformatics. 2006 Jun 1;22(11):1297-301
references: 16543275
references: J Bacteriol. 2008 Oct;190(20):6829-36
references: 18723619
references: Nat Rev Microbiol. 2010 Jan;8(1):39-50
references: 19966815
references: J Plant Physiol. 2007 Jan;164(1):11-8
references: 16603273
references: J Bacteriol. 2006 Sep;188(18):6694-9
references: 16952962
references: Curr Opin Microbiol. 2011 Oct;14(5):608-14
references: 21840247
references: Proc Natl Acad Sci U S A. 1992 Jun 15;89(12):5655-9
references: 1608976
references: Microbiology (Reading). 2012 Feb;158(Pt 2):345-352
references: 22053003
references: Proc Natl Acad Sci U S A. 1995 Sep 26;92(20):9358-62
references: 7568132
references: Mol Microbiol. 1998 Mar;27(6):1193-202
references: 9570404
references: J Bacteriol. 2001 Jan;183(1):280-6
references: 11114927
references: Proc Natl Acad Sci U S A. 2001 Feb 27;98(5):2729-34
references: 11226308
references: Environ Microbiol Rep. 2011 Oct;3(5):550-8
references: 23761334
references: ISME J. 2007 Aug;1(4):354-60
references: 18043646
references: J Bacteriol. 2008 Dec;190(23):7645-54
references: 18835986
references: Z Allg Mikrobiol. 1976;16(6):453-63
references: 824870
references: Lett Appl Microbiol. 2009 Sep;49(3):332-7
references: 19627483
references: J Bacteriol. 2011 Nov;193(21):6070-4
references: 21890704
references: J Gen Microbiol. 1984 Apr;130(4):789-96
references: 6204007
references: PLoS One. 2010 Jul 08;5(7):e11486
references: 20628610
references: EMBO J. 1990 Oct;9(10):3379-88
references: 2120040
references: BMC Evol Biol. 2011 Jun 30;11:187
references: 21718514
references: Toxicon. 1999 Oct;37(10):1359-73
references: 10414862
references: Curr Biol. 2010 Sep 14;20(17):1557-61
references: 20705465
references: Ecotoxicol Environ Saf. 2003 Jun;55(2):243-50
references: 12742375
references: Nucleic Acids Res. 1997 Sep 1;25(17):3389-402
references: 9254694
references: PLoS One. 2010 Mar 10;5(3):e9490
references: 20224823
references: Mol Ecol. 2003 Jan;12(1):133-40
references: 12492883
references: Science. 2001 Nov 16;294(5546):1534-7
references: 11711677
references: FEMS Microbiol Ecol. 2012 Mar;79(3):800-11
references: 22126519
references: Bioinformatics. 2005 Mar 1;21(5):676-9
references: 15509596
references: Proteomics. 2011 Feb;11(3):406-19
references: 21268270
references: Mol Microbiol. 2005 Oct;58(1):227-43
references: 16164561
references: Nucleic Acids Res. 2004 Mar 19;32(5):1792-7
references: 15034147