Title: Defining Core Genotypes and Phenotypes of the Last Common Ancestors What about Nitrogen
1Defining Core Genotypes and Phenotypes of the
Last Common Ancestor(s)What about Nitrogen?
2Nitrogen 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
35 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
4Nif 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
5Group 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(No Transcript)
7Unifying the 5 gene and rRNA species trees
8Most 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?)
9Thanks
- 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