Question 1

Which process is primarily responsible for the conversion of nitrate ($NO_3^-$) to ammonium ($NH_4^+$) in the US Great Basin hot springs studied in the article?

Accepted Answer

Dissimilatory nitrate reduction to ammonium (DNRA)

Question 2

What evidence supports the presence of ammonia-oxidizing archaea in the Great Basin hot springs?

Accepted Answer

Identification of 16S rRNA gene sequences specific to ammonia-oxidizing archaea

Question 3

In the context of the nitrogen biogeochemical cycle, which equation best represents the process of DNRA?

Accepted Answer

$NO_3^- \rightarrow NO_2^- \rightarrow NH_4^+$

Question 4

Why is the presence of DNRA in geothermal environments significant for primary productivity?

Accepted Answer

It recycles nitrogen into a form ($NH_4^+$) that is readily usable by many microorganisms.

Question 5

Which experimental approach was used to measure ammonia oxidation rates in the hot spring sediments?

Accepted Answer

Addition of $^{15}NH_4^+$ and measurement of $^{15}NO_2^-$ production

Question 6

What was the effect of acetylene addition in the experiments measuring $NO_2^-$ production?

Accepted Answer

It blocked ammonia oxidation, resulting in decreased $NO_2^-$ production.

Question 7

Based on the study, which of the following best describes the relationship between temperature and ammonia oxidation rates in the hot springs?

Accepted Answer

Ammonia oxidation rates are highest at moderate temperatures (50–60°C).

Question 8

Which microbial process is indicated by the following equation?

$NH_4^+ + 1.5 O_2 \rightarrow NO_2^- + 2 H^+ + H_2O$

Accepted Answer

Ammonia oxidation (nitrification)

Question 9

In the experiments, what was the main source of $NO_2^-$ detected in the sediment slurries?

Accepted Answer

Microbial ammonia oxidation

Question 10

Why was $^{15}NO_3^-$ used in the denitrification rate experiments?

Accepted Answer

To measure the production of $^{15}N_2$ gas as evidence of denitrification

Question 11

Which of the following statements best explains why DNRA is favored over denitrification in the studied hot springs?

Accepted Answer

High temperatures and abundant electron donors promote DNRA.

Question 12

If a sediment sample from a hot spring shows high rates of $NH_4^+$ production but low $N_2$ gas emission, which process is most likely dominant?

Accepted Answer

DNRA

Question 13

What is the ecological significance of ammonia-oxidizing archaea in geothermal environments?

Accepted Answer

They facilitate the conversion of $NH_4^+$ to $NO_2^-$, supporting nitrogen cycling.

Question 14

Which of the following best describes the role of acetylene in the experimental setup?

Accepted Answer

It inhibits ammonia monooxygenase, blocking ammonia oxidation.

Question 15

A multi-step calculation: If the ammonia oxidation rate in a sediment slurry is $6.7$ nmol $NO_2^-$ g$^{-1}$ h$^{-1}$ and the slurry contains $2$ g of sediment, how much $NO_2^-$ (in nmol) would be produced in $5$ hours?

Use the formula:

$	ext{Total } NO_2^- = 	ext{Rate} 	imes 	ext{Mass} 	imes 	ext{Time}$

Accepted Answer

$6.7 	imes 2 	imes 5 = 67$ nmol

Question 16

Which of the following is NOT a plausible reason for the observed high rates of DNRA in the Great Basin hot springs?

Accepted Answer

High oxygen concentrations in spring water

Question 17

In the context of the study, which nitrogen transformation process would be most affected if ammonia-oxidizing archaea were absent from the hot spring sediments?

Accepted Answer

Ammonia oxidation (nitrification)

Question 18

Which of the following best describes the main conclusion of the study?

Accepted Answer

DNRA and ammonia oxidation are both active, with ammonia-oxidizing archaea playing a key role in nitrogen cycling.

Question 19

Which molecular technique was used to identify microbial populations in the hot spring sediments?

Accepted Answer

16S rRNA gene sequencing

Nitrate Reduction to Ammonium and Ammonia-Oxidizing Archaea in US Great Basin Hot Springs

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