1. Georgia Tech School of Biology Summer 2012Bio@Tech Microbes in the Biosphere From Whitman et al. 1998 PNAS 95:6578-6583: 4 x 10 30 prokaryotic cells on Earth – Subsurface ~3.8 x 10 30 – Aquatic ~1 x 10 29 – Soils~2.5 x 10 29 – Animals (termites)~5 x 10 24 – Air~ 5 x 10 19 If laid end to end, would span Earth-Sun distance one trillion (10 12 ) times. 350-550 Pg C = 60-100% of C in plants 90% of organic N, P

2. Georgia Tech School of Biology Summer 2012 Microbes R Us 70 x 10 12 prokaryotic cells per person – Mostly in gut: colon has 300 x 10 9 /g – Gut microbiome > 100 x human genome Human microbiome project Bio@Tech

3. Georgia Tech School of Biology 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. BacteriaEukaryaArchaea 4Symbiosis of chloroplast ancestor with ancestor of green plants 3Symbiosis of mitochondrial ancestor with ancestor of eukaryotes 2Possible fusion of bacterium and archaean, yielding ancestor of eukaryotic cells 1Last common ancestor of all living things 4 3 2 1 1 2 3 4 0 Billion years ago Origin of life Campbell & Reece, Fig. 25.18

4. Georgia Tech School of Biology Summer 2012Bio@Tech Evolutionary Time Life originated about 4 billion years ago. Living organisms have fundamentally altered Earth. Campbell & Reece, Fig. 26.10

5. Georgia Tech School of Biology Summer 2012Bio@Tech History of life on Earth

6. Georgia Tech School of Biology 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)

7. Georgia Tech School of Biology Summer 2012 Stromatolites Stromatolite fossils are structurally indistinguishable from living examples Campbell & Reece, Fig. 26.11

8. Georgia Tech School of Biology Summer 2012 Microbes are planetary engineers Invented all metabolism – Catabolism – Anabolism Depleted ocean of dissolved iron (Fe 2+ ) – Anoxygenic photosynthesis 4 Fe 2+ + CO 2 + 4 H +  4 Fe 3+ + CH 2 O + H 2 O – Oxygenic photosynthesis H 2 O + CO 2 +  CH 2 O + O 2 4 Fe 2+ + O 2 + 4 H +  4 Fe 3+ + 2 H 2 O And injected oxygen into atmosphere! Bio@Tech

9. Georgia Tech School of Biology Summer 2012 Banded Iron Formations (Image courtesy of Dr. Pamela Gore, Georgia Perimeter College) (Hayes, 2002, Nature 417: 127-128)

10. Georgia Tech School of Biology Summer 2012 How did bacteria and archaea get energy before oxygen? Bio@Tech

11. Georgia Tech School of Biology Summer 2012 Respiration = oxidation/reduction Higher-energy molecules are oxidized (lose electrons) Lower-energy molecules are reduced (gain electrons)  G = -nF  E (kJ/mol) – n = # e- transferred – F = Faraday constant –  E = redox potential difference

12. Georgia Tech School of Biology Summer 2012 Respiration: electrons from NADH charge a membrane pH gradient NADH Electron donors {[CH 2 O], H 2, H 2 S, CH 4, Fe 2+, etc.} Terminal electron acceptors O 2, NO 3 -, SO 4 2-, Mn 4+, Fe 3+, CO 2, etc. H + electrochemical gradient Electron transport chain NAD+ Plasma membrane H+ See also: http://www.microbelibrary.org/images/Tterry/anim/ ETSbact.html

13. Georgia Tech School of Biology Summer 2012 NAD+/NADH is the cell’s main electron (hydrogen) carrier NAD = nicotinamide adenine dinucleotide. For NADH + H + +1/2 O 2 ↔ NAD+ + H 2 O, ΔG o = -52.4 kcal/mol.

14. Georgia Tech School of Biology Summer 2012 Terminal Electron Acceptors Different e - acceptors are used sequentially in microbial ecosystems, reflecting the energy yields of different pathways. – O 2 ∆G = -479 kJ mol -1 – NO 3 - ∆G = -453 kJ mol -1 – Mn 4+ ∆G = -349 kJ mol -1 – Fe 3+ ∆G = -114 kJ mol -1 – SO 4 2- ∆G = -77 kJ mol -1

15. Georgia Tech School of Biology Summer 2012 Redox Stratification in Marine Sediments (Jorgensen 2000, Fig. 5.11)

16. Georgia Tech School of Biology Summer 2012 Proton gradient across the plasma membrane drives chemiosmotic ATP synthesis and active transport Fenchel, Origin & Early Evolution of Life, Oxford U Press 2002, Fig 6.2

17. Georgia Tech School of Biology Summer 2012 Oxidative phosphorylation F1 ATPase video Periplasmic space Rotor H+H+ Stator Internal rod Cata- lytic knob ADP + P ATP i Cytoplasm F0 portion in membrane -resembles flagellar motor F1 portion (ATP synthase) -resembles DNA helicase See also: http://www.microbelibrary.org/images/Tterry/ani m/ATPsynthbact.html http://www.youtube.com/watch?v=PjdPTY1wHdQ

18. Georgia Tech School of Biology 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

19. Georgia Tech School of Biology Summer 2012 Extraction of electrons from carbohydrates to reduce NAD+ GlycolysisCitric acid cycle NADH Glucose, NAD+, ADP H + electrochemical gradient Pyruvate oxidation ETC ATP NADH + FADH 2 NADH ADP CO 2 NAD+ADPNAD+ FAD

20. Georgia Tech School of Biology Summer 2012 A soil-based microbial fuel cell Bio@Tech