Question 1

Which of the following best describes the 'Great Plate Count Anomaly' in microbial ecology?

Accepted Answer

It refers to the observation that most microbes in environmental samples cannot be cultured using standard laboratory techniques.

Question 2

Which method would you use to identify the phylogenetic composition of a microbial community without culturing the organisms?

Accepted Answer

16S rRNA gene census

Question 3

A researcher wants to measure the rate of sulfate reduction in a sediment sample. Which of the following would be the most appropriate approach?

Accepted Answer

Measure the accumulation of $$\mathrm{H_2S}$$ using a chemical assay and include a killed control treated with formaldehyde.

Question 4

Which of the following equations correctly represents lactate oxidation coupled to sulfate reduction?

Accepted Answer

$$\mathrm{C_3H_5O_3^- + 1.75\ SO_4$^{2-} \rightarrow 3\ $$HCO_3$$^- + 1.75\ HS^- + 0.25\ H^+}$$

Question 5

Why is it important to include a 'killed' control (e.g., formaldehyde-treated sample) when measuring microbial activity in environmental samples?

Accepted Answer

To distinguish between biotic and abiotic reactions in the sample.

Question 6

Which of the following best describes the principle of FISH (Fluorescence In Situ Hybridization) in microbial ecology?

Accepted Answer

It uses fluorescently-labeled oligonucleotide probes to bind to specific rRNA sequences in intact cells, allowing visualization of specific phylogenetic groups.

Question 7

A scientist uses $$^{14}C-$$glucose to measure glucose respiration in a soil sample. What is the main metabolic product being measured, and how is it detected?

Accepted Answer

The main product is $$^{14}CO$_2$$, detected by measuring radioactivity.

Question 8

Which of the following is a key advantage of using stable isotope probing (SIP) in microbial ecology?

Accepted Answer

It links metabolic activity to specific organisms by tracking incorporation of labeled substrates into biomolecules.

Question 9

Which of the following statements about isotopic fractionation is correct?

Accepted Answer

Different enzymes and pathways can impart distinct isotopic fractionation patterns, which can be used to infer metabolic processes.

Question 10

A researcher is using a microsensor to measure oxygen concentration in a microbial mat. According to Fick's First Law, what is the relationship between diffusion flux ($$J) $$and the concentration gradient ($$\frac{dC}{dx}$$)?

Accepted Answer

$$J = -D \frac{dC}{dx}$$

Question 11

Which of the following best explains why 16S rRNA gene sequencing is a particularly useful biomarker in microbial ecology?

Accepted Answer

The 16S rRNA gene is highly conserved among prokaryotes but contains variable regions that allow discrimination between different taxa.

Question 12

Which of the following techniques allows for the visualization and quantification of specific microbial groups in situ, and can be combined with microautoradiography to link identity and function?

Accepted Answer

FISH-MAR (Fluorescence In Situ Hybridization-Microautoradiography)

Question 13

In an experiment measuring hydrogen oxidation coupled to sulfate reduction, which of the following would indicate that the observed sulfate reduction is due to microbial activity?

Accepted Answer

Sulfate reduction occurs in the live sample but not in the killed control.

Question 14

Which of the following is a limitation of bulk community activity measurements in microbial ecology?

Accepted Answer

They measure overall process rates but do not identify which organisms are responsible.

Question 15

A scientist is using BONCAT (Bioorthogonal Noncanonical Amino Acid Tagging) to study microbial activity. What is being detected with this method?

Accepted Answer

Cells actively synthesizing proteins by incorporating a methionine analog.

Question 16

Which of the following best describes the use of environmental genomics and microarrays in microbial ecology?

Accepted Answer

They allow for the analysis of gene content and expression in entire microbial communities without the need for cultivation.

Question 17

Which of the following is a real-world application of stable isotope analysis in microbial ecology?

Accepted Answer

Tracing the source of nutrients in a contaminated aquifer by measuring $$\$$delta^{13}$$C$$ values in microbial biomass.

Question 18

Which of the following statements about fluorescence microscopy with DNA-specific stains is correct?

Accepted Answer

SYTO-9 can enter both live and dead cells, while propidium iodide only enters dead cells.

Question 19

A researcher wants to infer the spatial distribution of microbial guilds in a biofilm. Which tool would provide the necessary spatial resolution and chemical sensitivity?

Accepted Answer

Microsensors capable of measuring gradients of chemicals such as $$\mathrm{O_2$}$$, $$\mathrm{H_2S}$$, and pH at micrometer scales.

Cultivation-Independent Methods in Microbial Ecology: Microbial Activities

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