Microbial Iron Cycle Quiz

Which oxidation state of iron is predominantly used as an electron donor in microbial iron oxidation?

• Fe³⁺

• Fe²⁺

• Fe⁰

• Fe⁴⁺

Which group of bacteria is primarily responsible for the oxidation of Fe²⁺ under acidic conditions?

• Geobacter

• Acidithiobacillus

• Shewanella

• Nitrosomonas

What is the main product of microbial iron oxidation in neutral pH environments?

• Ferrihydrite

• Magnetite

• Goethite

• Pyrite

Answer explanation

At neutral pH, microbial iron oxidation often leads to the formation of ferrihydrite, an amorphous iron oxide.

Which type of bacteria can reduce Fe³⁺ to Fe²⁺ under anaerobic conditions?

• Nitrifying bacteria

• Sulfate-reducing bacteria

• Iron-reducing bacteria

• Methanogenic bacteria

In the microbial iron cycle, which process is typically coupled with the oxidation of Fe²⁺?

• Nitrate reduction

• Sulfate reduction

• Methane oxidation

• Oxygen reduction

What is the primary electron acceptor used by iron-reducing bacteria in anoxic environments?

• Sulfate (SO₄²⁻)

• Ferric iron (Fe³⁺)

• Oxygen (O₂)

• Nitrate (NO₃⁻)

Which of the following is a key intermediate in dissimilatory iron reduction?

• Ferrihydrite

• Magnetite

• Goethite

• Siderite

Answer explanation

Magnetite (Fe₃O₄) is a common intermediate formed during microbial reduction of Fe³⁺ to Fe²⁺.

What is the ecological significance of microbial iron reduction in sediments?

• Produces methane as a byproduct

• Detoxifies heavy metals

• Facilitates the cycling of organic carbon

• Converts ferric iron into hematite

Answer explanation

Microbial iron reduction plays a critical role in carbon cycling by coupling the oxidation of organic matter with the reduction of ferric iron.

Which metabolic pathway is used by Shewanella species for iron reduction?

• Methanogenesis

• Dissimilatory metal reduction

• Oxidative phosphorylation

• Fermentation

Answer explanation

Shewanella uses dissimilatory metal reduction to reduce Fe³⁺ to Fe²⁺ during anaerobic respiration.

What type of environmental conditions favor microbial iron oxidation by phototrophic bacteria?

• Acidic and aerobic

• Alkaline and anaerobic

• Neutral and anoxic with light

• Acidic and anoxic

Answer explanation

Phototrophic iron-oxidizing bacteria thrive under anoxic conditions in the presence of light, using Fe²⁺ as an electron donor for photosynthesis.