FINAL Week 8 Microbial Evolution, Biogeochem and Elemental Cycles

Question 1

Metabolic phenotype of first primitive cells

Answer 1

1. Strictly Anaerobes (fermentation of anaerobic respiration)
2. Chemolithotrophic or methanogenic
3. Inhospitable surface conditions –> may have lived on subsurface habitats

Question 2

Deep Ocean Hydrothermal Vent Hypothesis

Answer 2

1. Supply of reduced inorganic compounds (e- donors)
   > AA, nitrogen bases, sugars react within carbonaceous silicate and clay mound matrix
2. Mineral rich (metals, elements, nutrients)
   > Fe3+, H+, Ni2+, CO2, PO4, Fe2+ and macromolecules&cofactors from prebiotic soup emerge to support DNA/RNA/proteins
3. Minerals, pH and redox –> biological molecule formation
   > Divergence of bacteria and archaea and global dispersal to new habitats/cell wall biochem/lipid biosynthesis
4. Primordial catalytic RNA
   > LUCA: organization into self-inclosed micelle structure

Question 3

Microbial Life on Early Earth

Answer 3

1. Stromatolites from ancient anoxygenic phototrophic microbes (green non-sulfur)
2. Banded iron formation:
   > evidence for atmospheric oxygenation (Cyanobacteria)
   > Dark bands: Fe3+ oxides; O2 is then free to accumulate in air

**Later: Populations –> guilds –> communities
> Species composition of habitat (niche) determined by redox material, nutrient and physical property availability

Question 4

Organo-lithotrophic redox cycling
d = donor
a = acceptor

Answer 4

1. Chemorgano:
   » CH2O (d) –> CO2
   » NO3, Mn(IV), Fe(III) (a) –> NH4, Mn(II), Fe(II) (d)
2. Chemolitho:
   » Opposite for 2nd one
   » O2, NO3, Mn(IV) (a) –> H2O, N2, Mn(I), H+ (d)

Question 5

Global Carbon Cycle

Answer 5

1. Majority CO2 release from microbial decomposition
2. Net CO2 fixation (photosynthesis) and respiration
   > Major sources from Earth’s crust, soils, oceans and fossil fuels
   > Keeling Curve: increase in CO2 proportional to increase in temperature

Question 6

Paper #2: Microbial Nanowires

Answer 6

Electrically conductive bacteria by Shewanella oneidensis strain MR-1
> Less microbial culture formation in excess e- acceptor culture, but more in limited culture
> Nutrients have to be in close proximity for microbes to take in via motility, but nanowires make it easier (usually patchily distributed and soluble)
> Pili-like appendages: proteinaceous EC filament; current ACROSS nanowires (not along) measured via Scanning Tunnel Microscopy (STM) and contacting with nanofabricated Pt electrodes

Question 7

Nanowire: more EC e- transfer

Answer 7

1. Provide Silica Hydrous Ferric oxide (solid Fe3+) as e- acceptor (metal reducing)
   > Reduction produces nanocrystalline magnetite (Fe3O4)
   > Genetic basis: decaheme c-type cytochrome (ETC)