nitrogen fixing ( diazotrophic ) phytoplankton: e.g
DESCRIPTION
Nitrogen fixing ( diazotrophic ) phytoplankton: e.g. Trichodesmium. 1 μm. Croccosphaera watsonii. 1 mm. Image: Annette Hynes. Image: WHOI. Where are diazotrophs? Trichodesmium. LaRoche and Breitbarth (2005) See also Sohm et al (2011), Luo et a (2012). - PowerPoint PPT PresentationTRANSCRIPT
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Nitrogen fixing (diazotrophic) phytoplankton: e.g.
Image: Annette Hynes
1 mm
1 μm
Trichodesmium
Croccosphaerawatsonii
Image: WHOI
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Where are diazotrophs?Trichodesmium
LaRoche and Breitbarth (2005) See also Sohm et al (2011), Luo et a (2012)
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Trade-offs defining diazotrophs
Relative to others, nitrogen fixers havefreedom from limitation by fixed nitrogenhigh cellular iron demand
Nitrogenaselow maximum growth rate
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Slow max growth rate
Breitbarth et al (2005) Temperature dependent growth rate of Trichodesmium
Moore et al (1995)Temperature dependent growth rate of picocyanobacteria
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Trade-offs define biogeography
Observations of Trichodesmium:Breitbarth and LaRoche (2005)
Model, all diazotrophs:Monteiro et al (2010)
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Interpret in terms of resource competition
Monteiro et al (2011) - following Tilman (1977), …
Ambient Fe concentration = minimum subsistence concentration
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Nitrogen fixing photo-autotroph
• Why slow growth rate?• Energetic cost of
breaking triple bond• Intracellular oxygen
management• Intracellular iron
management
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Respiration and growth rate
E. coli
Glycerol limited continuous cultureFarmer and Jones (1976)
Specific respiration rate (mol O
2 (g cell)
-1
s-1)
Dilution rate (= growth rate) (h-1)
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Respiration and growth rate
E. coli
Glycerol limited continuous cultureFarmer and Jones (1976)
Specific respiration (mol O
2 (g cell)
-1
s-1)
Dilution rate (= growth rate) (h-1)
Intercept: maintenance respiration
Slope related to efficiency (1/yield)
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Azotobacter vinelandiiFree living soil bacteriaOccupies aerobic environmentsFixes nitrogen asymbiotically
Post et al, Arch. Microbiol (1982)0.5μm
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Specific substrate consumption and growth rate as function of external
O2
• Azotobacter vinlandii
• Kuhler and Oelze (1988)
Increasing ambient [O2]
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Specific substrate consumption and growth rate as function of external
O2
• For same specific substrate supply, higher growth rate in lower oxygen environment
• Strong impact on maintenance uptake/respiration
• Oxygen management to preserve nitrogenase
• Azotobacter vinlandii
• Kuhler and Oelze (1988)
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Model• Conserve internal
fluxes of mass, electrons and energy• McCarty (1965),
Vallino et al (1996) …
• Biophysical model of substrate and O2 uptake• Pasciak and Gavis
(1974), Staal et al (2003), …
Keisuke Inomura
pyruvate
“biomass”
sucroseNH4+
O2
CO2
O2
CO2
N2
C5H7O2N
Moleculardiffusion
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Keisuke Inomura
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Oxygen management over-rides energetic demandMaintenance (intercept) very sensitive to cell sizeModeled yields too high
“biomass” stoichiometry?exudation of fixed N?
Keisuke Inomura
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SummaryProvided appropriate physiological trade-offs and environment are imposed, diverse system will plausibly self-organizeFor diazotrophs, slow population growth rate is a key traitCartoon “flux balance”/biophysical model captures key aspects of Azotobacter vinelandii growth
Model for e.g. Croccosphaera?Experimental data for marine organismMore general application…