Question 1

Which of the following statements best explains why 16S ribosomal RNA gene sequencing is widely used to distinguish bacterial phyla?

Accepted Answer

16S rRNA genes are universally present in all bacteria and contain both conserved and variable regions, making them ideal for phylogenetic analysis.

Question 2

A clinical microbiologist isolates a gram-negative, facultatively aerobic rod from a patient’s urine. The bacterium is catalase-positive, oxidase-negative, and ferments glucose to a mixture of acids. Which genus is this organism most likely to belong to?

Accepted Answer

Escherichia

Question 3

Which of the following best describes the metabolic diversity of the Proteobacteria?

Accepted Answer

They include phototrophs, chemolithotrophs, and chemoorganotrophs, with diverse energy generation mechanisms.

Question 4

A soil bacterium is isolated that forms root nodules in legumes and fixes atmospheric nitrogen. Which order does this bacterium most likely belong to?

Accepted Answer

Rhizobiales

Question 5

Which of the following is a distinguishing feature of the genus Wolbachia compared to Rickettsia?

Accepted Answer

Wolbachia can induce parthenogenesis and feminization in arthropod hosts, while Rickettsia cannot.

Question 6

Which of the following best explains why endospore formation is advantageous for soil-dwelling Firmicutes?

Accepted Answer

Endospores allow bacteria to survive in environments with variable nutrient levels, temperature, and water availability.

Question 7

A patient presents with symptoms of typhus. Which of the following bacteria is the most likely causative agent, and what is a key feature of its biology?

Accepted Answer

Rickettsia; obligate intracellular parasite transmitted by arthropod vectors

Question 8

Which of the following genera is known for producing antibiotics and is responsible for the characteristic earthy odor of soil?

Accepted Answer

Streptomyces

Question 9

A bacterium is isolated from a hot spring and is found to be an obligate chemolithotroph that uses $$\mathrm{H_2$} as an $$electron donor and $$\mathrm{O_2$} as an $$electron acceptor. It grows optimally at $$95^\circ \mathrm{C}. $$Which genus does this organism most likely belong to?

Accepted Answer

Aquifex

Question 10

Which of the following statements about Mycoplasma is correct?

Accepted Answer

Mycoplasma lack a cell wall and are resistant to antibiotics that inhibit cell wall synthesis.

Question 11

Which of the following best describes the fermentation pattern of Enterobacter aerogenes?

Accepted Answer

2,3-butanediol fermentation, producing butanediol, ethanol, and more $$\mathrm{CO_2$} as $$main products

Question 12

A bacterium isolated from the human large intestine is an obligate anaerobe, ferments polysaccharides, and synthesizes sphingolipids. Which genus does it most likely belong to?

Accepted Answer

Bacteroides

Question 13

Which of the following is a unique feature of Planctomycetes compared to most other bacteria?

Accepted Answer

They lack the cell division protein FtsZ and some have a membrane-enclosed nucleus-like structure.

Question 14

Which of the following genera is most likely to be found as a dominant member of the ocean photic zone and is considered one of the most abundant bacterial species on Earth?

Accepted Answer

Pelagibacter (P. ubique)

Question 15

A patient is diagnosed with a urinary tract infection caused by a highly motile, urease-producing, gram-negative rod that is capable of swarming. Which genus is most likely responsible?

Accepted Answer

Proteus

Question 16

Which of the following best explains the ecological significance of the genus Nitrospira?

Accepted Answer

Nitrospira oxidizes nitrite ($$\mathrm{NO_2$^-}) to $$nitrate ($$\mathrm{NO_3$^-}$$), playing a key role in the nitrogen cycle.

Question 17

Which of the following is a correct pairing of bacterial group and a unique structural or metabolic feature?

Accepted Answer

Verrucomicrobia: produce prosthecae and have peptidoglycan in their cell walls

Question 18

A bacterium is isolated from a dairy product and is found to be a rod-shaped, acid-tolerant, homofermentative lactic acid producer. Which genus does it most likely belong to?

Accepted Answer

Lactobacillus

Question 19

Which of the following best describes the life cycle of Chlamydia?

Accepted Answer

Alternates between an infectious elementary body and a replicative reticulate body within host cells.

Phylogenetic Diversity of Bacteria: Major Lineages and Key Groups

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