BigMoney Inc. has also had a major spill of inorganic NO2- that contaminated the

Question

BigMoney Inc. has also had a major spill of inorganic NO2- that contaminated the soil around their plant. Scientists at BigMoney have developed mechanisms for removing NO3- from soil, but have not found one for NO2-. They want to know, on a strictly theoretical basis (regardless of whether bacteria exist in nature that actually do these specific reactions), if there are any types of bacteria that could metabolize NO2- to give rise to NO3-. (6 points total) NO2- ? NO3- (0.421)

a) is this an oxidation or reduction?

b) is NO2- serving as an electron acceptor or donor?

c) Which of the following metabolisms (aerobic respiration, anaerobic respiration, aerobic chemolithotrophy and anaerobic chemolithotrophy) could be used to carry out this reaction? You can assume the reaction given above is either the initial oxidation reaction or the final reduction reaction. You must think about whether each of these metabolisms can oxidize or reduce inorganic materials. Remember, think strictly theoretically. Note, you must indicate ALL metabolisms that could be used. (1 point)

d) For each of the metabolisms that could be used, describe exactly how NO3- will be formed providing the following information: (5 points)

Is the initial electron donor (from where are the electrons being taken) organic or inorganic?

Which of the pathways discussed in class (glycolysis, TCA, electron transport chain, chemolithotrophy, photosynthesis, and fermentation) will be used to get the electrons?

Is the final electron acceptor oxygen or not oxygen, and is it organic or inorganic?

Please provide a specific example of a half reaction (either initial oxidation or final reduction) that would work with the half reaction provided in this scenario, and briefly describe why it was chosen. Hint: your answer must consider the reduction potential of the electron acceptor compared to that of the electron donor and the half equation given must be either the donating or accepting reaction. Note: you may assume other molecules, both organic and inorganic, are present in the soil.

Explanation / Answer

Nitrifying bacteria are chemolithotrophic organisms that include species of the genera Nitrosomonas, Nitrosococcus, Nitrobacter and Nitrococcus. These bacteria get their energy by the oxidation of inorganic nitrogen compounds.They convert the most reduced form of soil nitrogen, ammonia, into its most oxidized form, nitrate. In itself, this is important for soil ecosystem function, in controlling losses of soil nitrogen through leaching and denitrification of nitrate. Nitrifiers also contribute to other important processes, including nitrous oxide production, methane oxidation, degradation of organic compounds, and carbon monoxide oxidation.

Nitrifying bacteria that oxidize nitrite are:

GENUS

PHYLOGENETIC GROUP

HABITATS

CHARACTERISTICS

Nitrobacter

Alpha

Soil, Freshwater, Marine

Short rods, reproduce by budding, occasionally motile (single subterminal flagella) or non-motile; membrane system arranged as a polar cap

Nitrospina

Delta

Marine

Long, slender rods, nonmotile, no obvious membrane system

Nitrococcus

Gamma

Marine

Large Cocci, motile (one or two subterminal flagellum) membrane system randomly arranged in tubes.

Nitrospira

Nitrospirae

Soil, Marine

Helical to vibroid-shaped cells; nonmotile; no internal membranes.

Thus, we can say that this is an oxidation reaction.

Nitric Oxide as an Electron Donor.

Chemolithotrophy is the oxidation of inorganic chemicals for the generation of energy. The process can use oxidative phosphorylation, just like aerobic and anaerobic respiration, but now the substance being oxidized (the electron donor) is an inorganic compound. The electrons are passed off to carriers within the electron transport chain, generating a proton motive force that is used to generate ATP with the help of ATP synthase.

Anaerobic chemolithotrophyis used to carry out this reaction.

GENUS

PHYLOGENETIC GROUP

HABITATS

CHARACTERISTICS

Nitrobacter

Alpha

Soil, Freshwater, Marine

Short rods, reproduce by budding, occasionally motile (single subterminal flagella) or non-motile; membrane system arranged as a polar cap

Nitrospina

Delta

Marine

Long, slender rods, nonmotile, no obvious membrane system

Nitrococcus

Gamma

Marine

Large Cocci, motile (one or two subterminal flagellum) membrane system randomly arranged in tubes.

Nitrospira

Nitrospirae

Soil, Marine

Helical to vibroid-shaped cells; nonmotile; no internal membranes.

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