In biogeochemical cycling, distinct microenvironments within soil ecosystems determine the… — JAMB UTME

In biogeochemical cycling, distinct microenvironments within soil ecosystems determine the specific microbial metabolic pathways that take place. Match each biochemical nitrogen transformation listed on the left with the exact bacterial genus and metabolic condition responsible for it on the right.

Direct reduction of nitrate ( $NO_3^-$ ) into gaseous dinitrogen ( $N_2$ )Pseudomonas operating under anoxic/waterlogged soil conditions
Chemoautotrophic oxidation of nitrite ( $NO_2^-$ ) into nitrate ( $NO_3^-$ )Nitrobacter operating under well-oxygenated soil conditions
Free-living aerobic conversion of atmospheric dinitrogen ( $N_2$ ) into ammonia ( $NH_3$ )Azotobacter operating independently in aerobic terrestrial environments
Free-living anaerobic reduction of atmospheric dinitrogen ( $N_2$ ) in saprophytic soilsClostridium operating in oxygen-depleted saprophytic habitats

Answer

The biochemical nitrogen transformations match their respective microbial genera and environmental conditions as follows: Reduction of nitrate to gaseous dinitrogen pairs with Pseudomonas operating under anoxic conditions; Oxidation of nitrite to nitrate pairs with Nitrobacter operating under well-oxygenated conditions; Free-living aerobic nitrogen fixation pairs with Azotobacter operating in aerobic environments; Free-living anaerobic nitrogen fixation pairs with Clostridium operating in oxygen-depleted saprophytic habitats.

Each nitrogen transformation requires specific enzymatic machinery and oxygen tensions: Pseudomonas carries out anaerobic denitrification (

NO_3^- \rightarrow N_2

), Nitrobacter oxidizes nitrite to nitrate (

NO_2^- \rightarrow NO_3^-

) aerobically, Azotobacter conducts free-living aerobic nitrogen fixation, and Clostridium carries out free-living anaerobic nitrogen fixation.

Step-by-Step Solution

Identify the organism and metabolic environment responsible for reducing nitrate to nitrogen gas (denitrification).

Pseudomonas functions under anoxic/waterlogged conditions to reduce

NO_3^-

N_2

gas.

Denitrification is an anaerobic respiration process where nitrate serves as the terminal electron acceptor.

Analyze the chemoautotrophic steps of nitrification in oxygenated soils.

Nitrosomonas converts ammonia to nitrite, whereas Nitrobacter oxidizes nitrite (

NO_2^-

) to nitrate (

NO_3^-

Nitrobacter relies strictly on aerobic oxidation of nitrite for metabolic energy.

Differentiate free-living nitrogen-fixing bacteria based on their oxygen requirements.

Azotobacter fixes atmospheric nitrogen aerobically, while Clostridium fixes nitrogen under anaerobic conditions.

Though both are free-living (non-symbiotic) nitrogen fixers, their respiratory enzymes dictate distinct ecological niches.

Key Concept

Microbial metabolic specificity and microenvironmental requirements in the biogeochemical nitrogen cycle

Estimated Time:2m 0s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic