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Defining Core Genotypes and Phenotypes of the Last Common Ancestors What about Nitrogen

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WHY: Its essential, must be fixed, found only in prokaryotes (diazatrophs) ... Jim Kasting, PSU. Initial interest. Fani group. NASA Exobiology, NSF LExEn ... – PowerPoint PPT presentation

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Title: Defining Core Genotypes and Phenotypes of the Last Common Ancestors What about Nitrogen


1
Defining Core Genotypes and Phenotypes of the
Last Common Ancestor(s)What about Nitrogen?
2
Nitrogen fixation
  • WHY Its essential, must be fixed, found only in
    prokaryotes (diazatrophs), expensive (16 atps).
  • WHERE Been recruited into many pathways,
    bacteriochlorophyll biosynthesis, FeS cluster
    assembly and insertion
  • WHEN Dwindling fixed nitrogen supplies,
    increasing biomass- pressure to find a way to fix
    from the atmosphere?
  • Navarro-Gonzalez, McKay and Mvondo 2001
  • Present in the Last common ancestor?
  • Fani, et al 2000.
  • HOW gene duplication, operon, HGT

3
5 Genes NIF H D K E N NIF H - the e shuttle
Nif D and K- e to N2, contains cofactor,
FeMoCo NIF E and N processing of D
K Alternative nitrogenases AnfK, AnfD for
Fe-only, VnfK, VnfD for V-only less efficient
at reducing N2
NifK
NifD
NifH
4
Nif genes on an organismal phylogeny 16S rDNA
tree for NCBIs 90 complete genomes (and H.
mobilis) Dark blue indicates lineages with nif
operons present light blue indicates partial
operons present Genome sequencing bias towards
pathogens probably underplays the true natural
distribution of nitrogenase
5
Group I cyanobacteria aerobic proteobacter Group
II obligate anaerobes (methanosarcina, sulfate
reducers, clostridia (50 base insertion in NifD)
NifH
Group III alternative nitrogenases Group IV
uncharacterized nitrogenase homologs, many in
organisms which do not fix nitrogen. Group V
Protochlorophyllide and chlorophyllide reductase
6
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7
Unifying the 5 gene and rRNA species trees
8
Most parsimonious pathway reconstruction for
nitrogen fixations
  • Nitrogenases have undergone extensive but
    episodic evolution, probably a direct mirror of
    environmental pressure resulting in distinct
    classes
  • Typical/Mo-based Invented in the methanogens and
    horizontally transferred in 3 events to the
    bacteria.
  • Alternative (Fe/V) Fe-only is least specific for
    N2 and shows simplest operons, probably
    represents first functioning nitrogenase.
  • Atypical Not likely to be fixing nitrogen,
    though perhaps serve as a redox-active shuttle
    for excess reductant (to what? CN?)

9
Thanks
  • Nitrogenase work
  • Jason Raymond, Bob Blankenship, ASU
  • Submitted to Molecular Biology and Evolution
  • Paleo-atmosphere discussions
  • Jim Kasting, PSU
  • Initial interest
  • Fani group
  • NASA Exobiology, NSF LExEn
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