Biogeochemical cycling and redox reactions

Question 1

What is biogeochemical cycling?

Answer 1

microbial transformations of elements8 and compounds in the environment.

Question 2

Implications for the environment:

Answer 2

• primary production eg photosynthesis
• Organic matter degradation
• oxygen depletion -> anoxia
• Ocean acidification
• Toxic sulfide production
• Climate change (greenhouse gas production or removal)
• Contaminant removal ( petroleum hydrocarbon breakdown)

Question 3

What is reductive immobilization of Uranium by Geobacter sulfurreducens?

Answer 3

Uranium (6) is soluble in water, the bacterium can reduce that and gain energy from the reaction. From uranium 6 to uranium 4. The black spots are uranium for precipitate. So when it transforms to uranium 4, its drop out the solution. This can help to take uranium out from the groundwater

Question 4

Why microorganisms perform a different transformation in the environment?

Answer 4

• energy gain for the cell
• Carbon and nutrient assimilation( 同化）
• Resistance via detoxification - remove/ transform toxic substances, eg. heavy metal and metalloids like arsenic.

Question 5

what is arsenic resistance?

Answer 5

The organisms take in solid arsenate (As5+) which is insoluble. It reduces it to aqueous arsenate (As3+) and pumps back out. The As3+ is soluble and toxic to other organisms. This can cause a problem to drink water.

Question 6

What is dissimilatory?

Answer 6

Energy generation through electron transfer (REDOX)

Question 7

What is redox potential?

Answer 7

The tendency of molecules in a system to accept or donate an electron.

Question 8

what is organic carbon (OC) oxidation?

Answer 8

OC + O2 -> CO2 + H2O

Question 9

What is aerobic acetate oxidation?

Answer 9

CH3COO- + O2 -> CO2 + H2O

Question 10

What is a good donor (poor electron acceptor)?

Answer 10

Hydrogen

Question 11

What is a poor donor (good electron acceptor)?

Answer 11

Oxygen

Question 12

What are the major microbially influenced biogeochemical cycles?

Answer 12

Carbon, Nitrogen, sulfur

Question 13

What is eutrophication?

Answer 13

When the water becomes overly enriched with minerals and nutrients which induce excessive growth of algae

Question 14

What is intertidal Ulva intestinalis?

Answer 14

Grass-green seaweed that can’t fic N2, it needs agricultural ammonium/Nitrate promotes growth.

Question 15

What are the consequences of nitrogen excess?

Answer 15

causing carbon excess-> primary producer excess and high biomass

• heterotrophs (consumers): aerobic oxidation of organic carbon.
• Anoxia (lack of oxygen) and acidification
• use alternative electron acceptor (sulfate), resulting in toxic sulfide production.

Question 16

what is oxygen minimum zones (OMZs)?

Answer 16

• Water column depth of ~200 to 1000m
• Formation at the interface of:
  coastal upwelling of nutrient- and oxygen-rich water and falling organic matter.
• Oxygen-depleted due to aerobic microbial organic carbon respiration -> anaerobic N and S metabolism.
• Typical nitrite (NO2-) rich with some sulfidic zone (H2S/HS-)