Lecture 6&7

Question 1

The higher the E’o (volts) of electron acceptors the more energy the organism can gain from the reaction. List the Redox pair and give their E’o.

Answer 1

REDOX PAIR E’o (VOLTS)
O2/ H2O +0.82
NO 3-/ NO 2- +0.75
Fe 3+/ Fe 2+ +0.22
SO4 2-/ HS- -0.22

Question 2

What are Assimilatory & Dissimilatory processes?

Answer 2

Assimilatory (anabolism) incorporating S, N, Fe and other metals into biomolecules like proteins and nucleic acids.
Dissimilatory (catabolism) S, N, Fe and other metals are reduced to produce energy.

Question 3

What kind of iron do Fe 3+ reducers prefer, Hematite or Ferric oxyhydroxide?

Answer 3

Ferric oxyhydroxide which is amorphous.

Question 4

What are the only 2 Geobacter strains that been shown to biodegrade hydrocarbons using Fe 3+ reduction, and what hydrocarbons were degraded?

Answer 4

1) G. metallireducens (toluene and benzene)
2) G. toluenoxydans (toluene)

Question 5

What is a genetic marker for sulfur dissimilators?

Answer 5

dsrAB gene

Question 6

What are some key methanogenic environments?

Answer 6

contaminated aquifers
petroleum reservoirs
marine sediments
sewage digesters

Question 7

What two methoxylated aromatic compounds can be directly used by methanogens?

Answer 7

H2 + CO2 and Acetate (CH3OO-)

Question 8

What is a gene that encodes for methylreductase and is thus an indication of methanogenesis?

Answer 8

mcrA gene

Question 9

What is Syntrophy in anaerobic metabolism?

Answer 9

An interdependent lifestyle where degradation of a compound like a fatty acid or hydrocarbon by organism 1 is only thermodynamically favorable if the end product is kept at low concentrations by organism 2 metabolizing it.

Hydrocarbon ———-> Acetate ———–> Methane

Question 10

List 4 ways a syntroph and methanogen exchange H2/ acetate/ formate

Answer 10

1) Reverse electron transfer/ complexes (formate)
2) Flagella and chemotaxis
3) Cell-to-cell contact (nanowires/pili and direct electron exchange)
4) Cell signaling/ Biofilm (quorum sensing)