Georgia Tech School of Biology Summer 2012Bio@Tech Microbes in the Biosphere From Whitman et al....

Georgia Tech School of Biology

Summer 2012Bio@Tech

Microbes in the BiosphereFrom Whitman et al. 1998 PNAS

95:6578-6583:• 4 x 1030 prokaryotic cells on Earth

– Subsurface ~3.8 x 1030

– Aquatic ~1 x 1029

– Soils ~2.5 x 1029

– Animals (termites) ~5 x 1024

– Air ~ 5 x 1019

• If laid end to end, would span Earth-Sun distance one trillion (1012) times.

• 350-550 Pg C = 60-100% of C in plants• 90% of organic N, P


Summer 2012

Microbes R Us• 70 x 1012 prokaryotic cells per

person– Mostly in gut: colon has 300 x 109/g– Gut microbiome > 100 x human

genome

• Human microbiome project

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Summer 2012Bio@Tech

“Tree of Life”

• All organisms we know of on Earth today are descended from a common ancestor that lived about 4 billion years ago.

Bacteria Eukarya Archaea

4 Symbiosis of chloroplast ancestor with ancestor of green plants

3 Symbiosis of mitochondrial ancestor with ancestor of eukaryotes

2 Possible fusion of bacterium and archaean, yielding ancestor of eukaryotic cells

1 Last common ancestor of all living things

4

3

2

1

1

2

3

4

0

Billio

n years ag

o

Origin of life

Campbell & Reece, Fig. 25.18


Summer 2012Bio@Tech

Evolutionary Time

• Life originated about 4 billion years ago.

• Living organisms have fundamentally altered Earth.



Summer 2012Bio@Tech

History of life on Earth


Summer 2012

Microfossils

Cyanobacteria (Nostocales) from the Bitter Springs Chert, Central Oz, 850 Ma(J.W. Schopf, UCLA http://www.cushmanfoundation.orgt/slides/stromato.html)

2.5-2.7 Ga microfossils (Schopf, 2006. Phil. Trans. R. Soc. B 361: 869-885)


Summer 2012

Stromatolites

• Stromatolite fossils are structurally indistinguishable from living examples



Summer 2012

Microbes are planetary engineers• Invented all metabolism

– Catabolism– Anabolism

• Depleted ocean of dissolved iron (Fe2+)– Anoxygenic photosynthesis

• 4 Fe2+ + CO2 + 4 H+ 4 Fe3+ + CH2O + H2O

– Oxygenic photosynthesis• H2O + CO2 + CH2O + O2

• 4 Fe2+ + O2 + 4 H+ 4 Fe3+ + 2 H2O

• And injected oxygen into atmosphere!

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Summer 2012

Banded Iron Formations

(Image courtesy of Dr. Pamela Gore,Georgia Perimeter College)(Hayes, 2002, Nature 417: 127-128)


Summer 2012

How did bacteria and archaea get energy before oxygen?

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Summer 2012

Respiration = oxidation/reduction

• Higher-energy molecules are oxidized (lose electrons)

• Lower-energy molecules are reduced (gain electrons)

• G = -nFE (kJ/mol)– n = # e- transferred– F = Faraday constant– E = redox potential difference


Summer 2012

Respiration: electrons from NADHcharge a membrane pH gradient

NADH

Electron donors {[CH2O], H2, H2S, CH4, Fe2+, etc.}

Terminal electron acceptorsO2, NO3

-, SO42-, Mn4+, Fe3+,

CO2, etc.

H+ electrochemical gradient

Electron transport chain

NAD+

Plasma membrane

H+

See also:http://www.microbelibrary.org/images/Tterry/anim/ETSbact.html


Summer 2012

NAD+/NADH is the cell’s main electron (hydrogen) carrier

NAD = nicotinamide adenine dinucleotide.For NADH + H+ +1/2 O2 ↔ NAD+ + H2O, ΔGo = -52.4 kcal/mol.


Summer 2012

Terminal Electron Acceptors• Different e- acceptors are used sequentially

in microbial ecosystems, reflecting the energy yields of different pathways.

– O2 ∆G = -479 kJ mol-1

– NO3- ∆G = -453 kJ mol-1

– Mn4+ ∆G = -349 kJ mol-1

– Fe3+∆G = -114 kJ mol-1

– SO42- ∆G = -77 kJ mol-1


Summer 2012

Redox Stratification in Marine Sediments

(Jorgensen 2000, Fig. 5.11)


Summer 2012

Proton gradient across the plasma membrane drives chemiosmotic ATP synthesis and active

transport

Fenchel, Origin & Early Evolutionof Life, Oxford U Press 2002, Fig 6.2


Summer 2012

Oxidative phosphorylationF1 ATPase video

Periplasmic space

Rotor

H+

Stator

Internalrod

Cata-lyticknob

ADP+P ATP

i

Cytoplasm

F0 portion in membrane-resembles flagellar motorF1 portion (ATP synthase)-resembles DNA helicase

See also:http://www.microbelibrary.org/images/Tterry/anim/ATPsynthbact.html

http://www.youtube.com/watch?v=PjdPTY1wHdQ


Summer 2012

Q: If the proton concentration outside the cell is low, then

A. The rate of ATP synthesis will decrease

B. The rate of ATP synthesis will increase

C. ATP synthase will hydrolyze ATP and pump protons out of the cell

D. ATP synthase will hydrolyze ATP and pump protons into the cell


Summer 2012

Extraction of electrons from carbohydrates to reduce NAD+

Glycolysis Citric acid cycle

NADH

Glucose, NAD+, ADP

H+ electrochemical gradient

Pyruvate oxidation

ETC

ATPATP NADH + FADH2NADH

ADP

CO2 CO2NAD+ ADPNAD+FAD


Summer 2012

A soil-based microbial fuel cell

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