C16 Sample Questions from Brock

Question 1

Which phylum harbors the most functional diversity observed and also has the most cultured representatives?
A) Actinomycetota
B) Bacteroidota
C) Bacillota
D) Pseudomonadota

Answer 1

D) Pseudomonadota.

Pseudomonadota are incredibly diverse metabolically and represent a large portion of cultured bacteria.

Question 2

Isolating a bacterium of the _______ class would be of high impact due to it only having one cultured representative.
A) Alphaproteobacteria
B) Betaproteobacteria
C) Epsilonproteobacteria
D) Zetaproteobacteria

Answer 2

D) Zetaproteobacteria.

This class is known for having very few cultured representatives.

Question 3

A pink-pigmented facultative methylotrophic bacterium is LEAST likely to be classified as a member of
A) Rhizobiales.
B) Rhodobacter.
C) Methylobacterium.
D) Pseudomonadota.

Answer 3

A) Rhizobiales.

Rhizobiales are typically associated with plant roots and nitrogen fixation, not methylotrophy. Rhodobacter and Methylobacterium are known methylotrophs.

Question 4

Which genus would you most likely find in the photic layer of the oceans due to its abundance and aerobic chemoorganotrophic phenotype?
A) Acetobacter
B) Nitrosomonas
C) Paracoccus
D) Pelagibacter

Answer 4

D) Pelagibacter.

Pelagibacter ubique is one of the most abundant organisms in the ocean and is an aerobic chemoorganotroph.

Question 5

Which of the following traits is NOT a characteristic of Caulobacter?
A) abundant in aquatic habitats rich in nutrients
B) produces a cytoplasmic outgrowth (prostheca)
C) aerobic chemoorganotrophs
D) asymmetric cell division

Answer 5

A) abundant in aquatic habitats rich in nutrients.

Caulobacter prefer oligotrophic (nutrient-poor) aquatic environments.

Question 6

Biosynthesis of vitamin K (menaquinone) by _______ spp. inhabiting the ________ of humans is a potentially important mutualistic relationship for human health.
A) Bifidobacterium / intestinal tract
B) Bifidobacterium / stomach
C) Escherichia / intestinal tract
D) Escherichia / stomach

Answer 6

A) Bifidobacterium / intestinal tract.

Bifidobacterium species in the gut produce vitamin K, benefiting human health.

Question 7

A gram-negative, obligately aerobic, bacillus-shaped bacterium that can degrade a large variety of aromatic compounds (making them potentially useful for bioremediation) is likely a(n)
A) actinobacterium.
B) enteric.
C) pseudomonad.
D) sphingomonad.

Answer 7

C) pseudomonad.

Pseudomonads are known for their ability to degrade a wide range of aromatic compounds.

Question 8

A pseudomonad that loses its R plasmid in the soil is LEAST likely to
A) cause an infection in a human.
B) colonize a surface.
C) infect a shrub.
D) survive a habitat dominated by antibiotic-producing Streptomyces

Answer 8

D) survive a habitat dominated by antibiotic-producing Streptomyces

The R plasmid typically confers antibiotic resistance, which is a crucial survival advantage for the pseudomonad in an environment where it is exposed to antibiotics produced by Streptomyces. Without the R plasmid, the pseudomonad would be more susceptible to the antibiotics and, therefore, less likely to survive and thrive in that habitat.

Question 9

Which of the following is NOT a member of the Deltaproteobacteria?
A) Campylobacter
B) Desulfovibrio
C) Geobacter
D) Syntrophobacter

Answer 9

A) Campylobacter.

Campylobacter is an Epsilonproteobacteria. The others listed are Deltaproteobacteria.

Question 10

Which of the following is NOT a trait of rickettsias?
A) They are obligate intracellular parasites.
B) They lack cell walls.
C) They have not been cultivated in the absence of host cells.
D) Both the host and parasite are required in order to be alive and metabolically active.

Answer 10

B) They lack cell walls.

Rickettsias possess cell walls. They are obligate intracellular parasites, difficult to cultivate outside host cells, and require both host and parasite to be metabolically active.

Question 11

Which of the following best distinguishes deltaproteobacteria from epsilonproteobacteria?
A) Deltaproteobacteria are most commonly found at anoxic-oxic interfaces while epsilonbacteria are most commonly found in anoxic environements.
B) Many epsilonbacteria oxidize sulfur compounds, which could be produced by a sulfur-reducing deltaproteobacterium.
C) A sulfate-reducing epsilonbacterium produces sulfite, which a deltaproteobacterium reduces further to hydrogen sulfide.
D) An epsilonbacterium reduces sulfur compounds whereas all deltaproteobacteria oxidize sulfur compounds.

Answer 11

B) Many epsilonbacteria oxidize sulfur compounds, which could be produced by a sulfur-reducing deltaproteobacterium.

This highlights a key metabolic difference and potential syntrophic relationship between the two groups. Deltaproteobacteria are often sulfate- or sulfur-reducers, while many Epsilonproteobacteria are sulfur-oxidizers.

Question 12

Based on oxygen requirements and metabolic strategies, you would most likely isolate an epsilonproteobacterium from
A) anoxic and sulfate-rich waters.
B) a plantʹs rhizosphere.
C) sulfate-rich anoxic-oxic interfaces.
D) sulfide-rich soils.

Answer 12

C) sulfate-rich anoxic-oxic interfaces.

Epsilonproteobacteria often thrive in environments with gradients of oxygen and sulfur compounds.

Question 13

Which of the following is NOT true of Epsilonproteobacteria?
A) They include the genera Campylobacter and Helicobacter.
B) Many species require relatively low O2 levels to grow.
C) Epsilonproteobacteria are present in freshwater, marine systems, and terrestrial environments.
D) Epsilonproteobacteria are prolific metal reducers.

Answer 13

D) Epsilonproteobacteria are prolific metal reducers.

While some Epsilonproteobacteria can reduce certain metals, they are not known as prolific metal reducers. This is more characteristic of some other groups like Deltaproteobacteria (e.g., Geobacter).

Question 14

Which taxon is NOT gram-positive?
A) Actinomycetota
B) Bacillota
C) Sphingobacteria
D) Streptococcus

Answer 14

C) Sphingobacteria.

Sphingobacteria are part of the Bacteroidota phylum, which are gram-negative.

Question 15

Which feature(s) differentiate(s) Actinomycetota from Bacillota?
A) absence/presence of a cell wall
B) endospore production capability
C) motility and chemotaxis abilities
D) relative G+C content in their genomes

Answer 15

D) relative G+C content in their genomes.

Actinomycetota typically have high G+C content, while Bacillota have low G+C content.

Question 16

The order Lactobacillales within Bacillota is also called the lactic acid bacteria because these bacteria
A) can aerobically catabolize lactic acid.
B) can ferment lactate.
C) produce lactate.
D) uniquely require lactic acid as a precursor for cell wall biosynthesis.

Answer 16

C) produce lactate.

Lactic acid bacteria are named for their production of lactic acid as a major end product of fermentation.

Question 17

What would most likely result if an exponentially growing culture of Lactobacillus spp. fermenting glucose was accidentally transferred into a highly aerated environment?
A) Aerobic catabolism of glucose would begin rather than aerobic degradation, due to the presence of O2.
B) Fermentation of glucose would continue, because the cells are insensitive to O2 despite lacking aerobic metabolism capabilities.
C) The cells would halt their metabolism due to the presence of N2, which acts as a global repressor of fermentation in this group.
D) The population would die due to the presence of O2, because it is a strict anaerobe.

Answer 17

B) Fermentation of glucose would continue, because the cells are insensitive to O2 despite lacking aerobic metabolism capabilities.

Lactobacillus are aerotolerant anaerobes. They can’t use oxygen for respiration, but its presence doesn’t harm them. They will continue to ferment glucose regardless of the presence of oxygen.

Question 18

Which bacterial genus would be best to select for fermenting cabbage to make homemade sauerkraut?
A) Clostridium
B) Lactobacillus
C) Propionibacterium
D) Staphylococcus

Answer 18

B) Lactobacillus

Lactobacillus species are commonly used in sauerkraut production due to their ability to ferment cabbage and produce lactic acid, which preserves and flavors the product.

Question 19

Which species does NOT produce endospores?
A) Bacillus cereus
B) Clostridium pasteurianum
C) Listeria monocytogenes
D) Paenibacillus popilliae

Answer 19

C) Listeria monocytogenes

Listeria is a member of the Bacillota, but it belongs to a different branch than Bacillus and Clostridium, which are known endospore formers. Paenibacillus also forms endospores.

Question 20

A gram-negative, nonsporulating rod that is highly motile, oxidase negative, facultatively aerobic, ferments glucose, and urease-positive is likely to be of which genus?
A) Pseudomonas
B) Proteus
C) Lactobacillus
D) Rickettsia

Answer 20

B) Proteus

The characteristics described align with Proteus: Gram-negative, nonsporulating rod, highly motile (characteristic swarming motility), oxidase negative, facultatively anaerobic, glucose fermenter, and urease positive.

Question 21

A yogurt, which had ʺcontains live culturesʺon its label, was transferred onto an acidic carbohydrate-containing medium for selective enrichment. Eventually, isolates of the genus were obtained.
A) Lactobacillus
B) Leuconostoc
C) Peptococcus
D) Streptococcus

Answer 21

A) Lactobacillus

Live cultures in yogurt are typically Lactobacillus and Streptococcus species, but the acidic carbohydrate medium favors Lactobacillus.

Question 22

A moistened swab rubbed onto a personʹs forearm then onto a nutrient agar plate with 7.5% NaCl would most likely result in the isolation of ______ spp.
A) Clostridium
B) Halobacterium
C) Sarcina
D) Staphylococcus

Answer 22

D) Staphylococcus

Staphylococcus species are part of the normal skin flora and are tolerant of the high salt concentration (7.5% NaCl) used in the selective medium.

Question 23

The ability to form endospores in bacteria within Bacillales, Clostridiales, and Lactobacillales suggests the genotype/phenotype evolved
A) at least three separate times in these divergent orders.
B) at least once, and horizontal gene transfer among relatives explains its presence in other orders.
C) only once in an ancestor to these three orders, due to the high number of genes required.
D) either at least once and horizontal gene transfer among relatives occurred or once in a common ancestor.

Answer 23

D) either at least once and horizontal gene transfer among relatives occurred or once in a common ancestor.

While a common ancestor is possible, the phylogenetic distance between these orders, combined with the complexity of sporulation, makes horizontal gene transfer a plausible explanation as well. Further research is needed to definitively determine the evolutionary history.

Question 24

Which genus is most easily distinguishable from others below by occurring in cell clusters of 8 or more?
A) Peptostreptococcus
B) Sarcina
C) Staphylococcus
D) Streptococcus

Answer 24

B) Sarcina

Sarcina is characterized by its unique cuboidal arrangement of cells (packets of eight or more).

Question 25

Which organisms would most likely be isolated from aerobic growth conditions with acetate and a soil sample heated to 80°C for 10 minutes?
A) aerobic or facultative anaerobic acetogens
B) endospore-forming bacteria
C) hyperthermophilic heterotrophic bacteria
D) mycoplasmas

Answer 25

B) endospore-forming bacteria

Heating the soil sample to 80°C for 10 minutes would kill most vegetative cells, but endospores would survive. Acetate provides a carbon source for growth.

Question 26

Which of the following is LEAST commonly associated with endospore-forming bacteria?
A) They are coccus-shaped organisms.
B) They are primarily soil dwellers.
C) They can survive adverse environmental conditions.
D) They are saprophytic.

Answer 26

A) They are coccus-shaped organisms.

Endospore-forming bacteria are typically rod-shaped (bacillus). They are commonly found in soil, can survive harsh conditions (the purpose of the endospore), and are often saprophytic (decomposers).

Question 27

Which bacillus-shaped genus are primarily intracellular parasites of arthropods such as crustaceans and insects?
A) Coxiella
B) Klebsiella
C) Roseospirillum
D) Wolbachia

Answer 27

D) Wolbachia

Wolbachia are well-known intracellular parasites of arthropods.

Question 28

Campylobacter and Helicobacter are two genera within the class of
A) Alphaproteobacteria
B) Betaproteobacteria
C) Deltaproteobacteria
D) Epsilonproteobacteria

Answer 28

D) Epsilonproteobacteria

Campylobacter and Helicobacter are classified within the Epsilonproteobacteria.

Question 29

Which group in Bacteria lacks cell walls?
A) Corynebacterium
B) Mycoplasma
C) Sporosarcina
D) Mycoplasmatota

Answer 29

B) Mycoplasma

Mycoplasma is a genus within the phylum Mycoplasmatota, characterized by the lack of a cell wall.

Question 30

The need for additional supplementation of ________ make developing growth media to culture mycoplasmas especially challenging.
A) unsaturated fatty acids
B) sterols
C) vitamins
D) unsaturated fatty acids, sterols, and vitamins

Answer 30

D) unsaturated fatty acids, sterols, and vitamins

Mycoplasmas require these supplements due to their limited biosynthetic capabilities, a consequence of their small genomes.

Question 31

Snapping division is a hallmark trait of _______ which can be visualized under a microscope by ____________.
A) Actinobacteria / two adjacent cells linked, appearing as an M dividing into four
B) Actinobacteria / one cell appearing as a V dividing into two
C) Coryneform bacteria / two adjacent cells linked, appearing as an M dividing into four
D) Coryneform bacteria / one cell appearing as a V dividing into two

Answer 31

D) Coryneform bacteria / one cell appearing as a V dividing into two

Snapping division in Coryneform bacteria results in a characteristic “V” shape.

Question 32

Due to the presence of mycolic acids in the cell wall of Mycobacterium spp., the staining procedure can be used as a diagnostic tool to identify this genus.
A) acid-fast
B) DAPI
C) Gram
D) lipo

Answer 32

A) acid-fast

Mycolic acids in the cell wall of Mycobacterium make them resistant to decolorization by acid-alcohol during the acid-fast staining procedure.

Question 33

Which bacterial genus is LEAST related to the others listed?
A) Actinomyces
B) Mycobacterium
C) Nocardia
D) Streptomyces

Answer 33

D) Streptomyces

While all are Actinomycetota, Streptomyces are quite distinct in their morphology (filamentous) and ecology (soil-dwelling) compared to the others listed.

Question 34

A soil sample was diluted into a nutrient broth, then spread onto a plate and grown for one week at room temperature. Several colonies appeared dusty or fuzzy and yet were identified as bacteria—not as fungi. Which genus do these isolates likely belong in?
A) Actinomyces
B) Mycobacterium
C) Nocardia
D) Streptomyces

Answer 34

D) Streptomyces

The “dusty” or “fuzzy” appearance of the colonies is indicative of the filamentous growth habit of Streptomyces.

Question 35

The _____ produce over 500 characterized antibiotics.
A) Bacteroidota
B) mycobacteria
C) pseudomonads
D) streptomycetes

Answer 35

D) streptomycetes

Streptomyces are renowned for their prolific production of antibiotics.

Question 36

Members of the ______ are the most abundant bacteria present in the large intestine of humans and contain unusual ______ in their cell membranes.
A) Bacteroides / glycerolipids
B) Bacteroides / sphingolipids
C) Sphingobium / glycerolipids
D) Sphingobium / sphingolipids

Answer 36

B) Bacteroides / sphingolipids

Bacteroides are abundant in the human gut and possess sphingolipids in their membranes, which is unusual for bacteria.

Question 37

Bacteria in the phylum ______ occur as elementary or reticulate bodies depending on their life cycle stage, are obligate intracellular parasites, and also have relatively small genomes.
A) Bacteroidota
B) Chlamydiota
C) Planctomycetota
D) Rickettsia

Answer 37

B) Chlamydiota

The characteristics described – elementary and reticulate bodies, obligate intracellular parasitism, and small genomes – are hallmarks of the phylum Chlamydiota.

Question 38

Members of the ______ are particularly abundant in the oceans, chemoorganotrophic, rarely pathogenic, and often produce pigments when grown on complex media.
A) Clostridiales
B) Flavobacteriales
C) Pelagibacterales
D) Rhizobiales

Answer 38

B) Flavobacteriales

Flavobacteriales are known for their abundance in marine environments, chemoorganotrophic metabolism, infrequent pathogenicity, and pigment production.

Question 39

Bacteria in the phylum _______ occur as elementary or reticulate bodies depending on their life cycle stage, are obligate intracellular parasites, and also have relatively small genomes.
A) Bacteroidota
B) Chlamydiota
C) Planctomycetota
D) Rickettsia

Answer 39

B) Chlamydiota

Chlamydiota exhibit the characteristic elementary and reticulate bodies during their life cycle and are obligate intracellular parasites with reduced genomes.

Question 40

Which of the following is NOT a trait of the Planctomycetota?
A) undergo budding cell division
B) have intracellular compartmentalization
C) lack peptidoglycan
D) undergo plant symbiosis

Answer 40

D) undergo plant symbiosis

Planctomycetota are known for budding cell division, intracellular compartmentalization, and lack of peptidoglycan. They are not known for plant symbiosis.

Question 41

Which structural feature is common in BOTH Planctomycetota and Verrucomicrobiota but RARELY found in bacteria outside these two phyla?
A) intracellular compartmentalization
B) prosthecae appendages
C) sheathlike toga cell envelopes
D) tubulins

Answer 41

A) intracellular compartmentalization

Both Planctomycetota and Verrucomicrobiota exhibit intracellular compartmentalization, a feature rare in other bacteria.

Question 42

Despite ether-linked lipids being a hallmark of the Archaea, the thermophilic sulfate-reducing bacteria in ______ also contain ether-linked lipids, which suggests they may be more closely related to Archaea than many other groups in Bacteria.
A) Aquifex
B) Thermodesulfobacterium
C) Thermus
D) Verrucomicrobium

Answer 42

B) Thermodesulfobacterium

Thermodesulfobacterium is known for having ether-linked lipids, a characteristic typically associated with Archaea.