Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

17
Nitrogen fixing (diazotrophic) phytoplankton: e.g. mage: Annette Hynes 1 mm 1 μm Trichodesmium Croccosphaera watsonii Image: WHOI

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 Presentation

Transcript of Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Page 1: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Nitrogen fixing (diazotrophic) phytoplankton: e.g.

Image: Annette Hynes

1 mm

1 μm

Trichodesmium

Croccosphaerawatsonii

Image: WHOI

Page 2: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Where are diazotrophs?Trichodesmium

LaRoche and Breitbarth (2005) See also Sohm et al (2011), Luo et a (2012)

Page 3: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Trade-offs defining diazotrophs

Relative to others, nitrogen fixers havefreedom from limitation by fixed nitrogenhigh cellular iron demand

Nitrogenaselow maximum growth rate

Page 4: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Slow max growth rate

Breitbarth et al (2005) Temperature dependent growth rate of Trichodesmium

Moore et al (1995)Temperature dependent growth rate of picocyanobacteria

Page 5: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Trade-offs define biogeography

Observations of Trichodesmium:Breitbarth and LaRoche (2005)

Model, all diazotrophs:Monteiro et al (2010)

Page 6: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Interpret in terms of resource competition

Monteiro et al (2011) - following Tilman (1977), …

Ambient Fe concentration = minimum subsistence concentration

Page 7: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Nitrogen fixing photo-autotroph

• Why slow growth rate?• Energetic cost of

breaking triple bond• Intracellular oxygen

management• Intracellular iron

management

Page 8: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

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)

Page 9: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

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)

Page 10: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Azotobacter vinelandiiFree living soil bacteriaOccupies aerobic environmentsFixes nitrogen asymbiotically

Post et al, Arch. Microbiol (1982)0.5μm

Page 11: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Specific substrate consumption and growth rate as function of external

O2

• Azotobacter vinlandii

• Kuhler and Oelze (1988)

Increasing ambient [O2]

Page 12: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

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)

Page 13: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

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

Page 14: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Keisuke Inomura

Page 15: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

Oxygen management over-rides energetic demandMaintenance (intercept) very sensitive to cell sizeModeled yields too high

“biomass” stoichiometry?exudation of fixed N?

Keisuke Inomura

Page 16: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.
Page 17: Nitrogen fixing ( diazotrophic ) phytoplankton: e.g.

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…