Chemoheterotrophy

Question 1

Order of thermodynamic favourability for chemoheterotrophic respiration?

Answer 1

Aerobic chemoheterotrophy

Anaerobic chemoheterotrophy

• Dissimilatory Nitrate Reduction
• Dissimilatory Manganese Reduction
• Dissimilatory Iron Reduction
• Dissimilatory reduction of other metals/metalloids
• Dissimilatory Sulphate Reduction
• Methanogenesis

Question 2

Equation for aerobic chemoheterotrophic respiration?

Answer 2

Glucose + 6O2 –> 6CO2 + 6H2O

Question 3

TEA and PED for aerobic chemoheterotrophic respiration?

Answer 3

TEA = O2
PED = Organic Carbon e.g., glucose

Question 4

TEA and PED for anaerobic chemoheterotrophic respiration?

Answer 4

TEA = X (O2 is not available)
PED = Organic Carbon

Question 5

Is anaerobic chemoheterotrophic respiration reduction or oxidation?

Answer 5

Reduction

• E.g. Dissimilatory X reduction
• Where X has to be in the oxidised form, can accept e- and become reduced.

Question 6

Dissimilatory Nitrate Reduction reaction?

Answer 6

NO3- > NO2- > NO > N2O > N2

From +5 oxidation state to 0 (being reduced).

Question 7

Describe Dissimilatory Manganese Reduction

Answer 7

Mn-reducers are facultative anaerobes (can use O2 if available).

Usually Mn(VI)-oxides:

• Ubiquitous in soil (appear black)
• Cant cross cell membranes. Cells attach to mineral surfaces or use electron shuttle molecules.

E.g. Geobacter and Shewanella

Question 8

Describe Dissimilatory Iron Reduction

Answer 8

Fe-oxides:

• ubiquitous in soil/sediment (orange)
• Cant cross cell membranes. Cells attach to mineral surfaces or use electron shuttle molecules.

E.g., Geobacter and Shewanella

Question 9

What are electron shuttles?

Answer 9

Organic compounds either produced by the organism or already in the environment.

Question 10

Explain the example of uranium reduction in Dissimilatory reduction of metals/metalloids

Answer 10

U(VI) - oxidised form of uranium, soluble + mobile.

U(IV) - reduced form of uranium, insoluble, contained

Abiotic reduction of uranium is slow, bacteria speed up the process.
E.g., Geobacter and Shewanella (derive energy from reaction)

Form UO2 in reduction reaction.

Question 11

Describe Dissimilatory Sulphate Reduction

Answer 11

TEA = SO42-

• Often obligate anaerobes (die in oxic conditions)
• Found in anoxic environments with enough OM and sulphate
• SRB can grow chemolithoautotrophically if not enough organic C
• Can switch to Fe or Mn reduction as more favourable

Question 12

Describe Methanogenesis

Answer 12

• Anaerobic Archea
• Produces very little energy, easily outcompeted
• Not true respiration
• Anoxic, sulphate deficient environments

Question 13

Chemoheterotrophic methanogenesis reaction?

Answer 13

CH3COOH –> CH4 + CO2

Question 14

Chemolithoautotrophic methanogenesis reaction?

Answer 14

CO2 + 4H2 –> CH4 + 2H2O