Deck 25: Microbial Symbioses

Question 1

Why do symbionts often contain lower G+C content when compared to free- living organisms?

A) Replicating high G+C content genomes requires several additional enzymes, to break apart the strong triple bonds formed from GC pairs, which are rarely found in symbionts with relatively small genome sizes.
B) Symbionts usually do not have as many DNA repair mechanisms as free- living organisms, and two common spontaneous mutations change GC pairs into AT pairs.
C) Free- living organisms must have a more stable genome to survive; low G+C content organisms are often selected against in nature.
D) Ancestral symbionts had low GC content genomes by chance, and these low GC content genomes are passed onto their progeny.

Answer 1

B

Question 2

Unlike higher termites, lower termites contain

A) lignolytic bacteria.
B) lignolytic fungi.
C) cellulolytic protists.
D) all of the above.

Answer 2

C

Question 3

Which of the following is NOT true of human gut microbes?

A) They produce and excrete amino acids.
B) The population size is low, but diversity is high.
C) They help catabolize polysaccharides.
D) They are involved in the "maturing" of the gastrointestinal tract.

Answer 3

B

Question 4

Which compounds serve as major sources of energy in rumens?

A) acetic, butyric, and propionic acids
B) glucose and sucrose
C) dimethylsulfoniopropionate , gluconate, and protocatechuate
D) acetic acid and glucose

Question 5

Which of the following do algae most commonly associate with in a mutualistic relationship?

A) flatworms
B) clams
C) corals
D) snails

Question 6

Which bacterium contains a large Ti plasmid and causes crown gall disease in plants?

A) Agrobacterium tumefaciens
B) Butyrivibrio fibrisolvens
C) Agrobacterium rhizogenes
D) Aliivibrio fischeri

Question 7

Two main symbionts of termites are and _.

A) fungi / protists
B) bacteria / protists
C) archaea / bacteria
D) bacteria / fungi

Question 8

How is a bacteroid distinguished from a bacterial cell?

A) biochemical tests
B) 16S rRNA gene sequencing
C) cell morphology
D) all of the above

Question 9

What is the fate of H2 produced within a rumen?

A) released via eructation (belching)
B) used in acetogenesis
C) used in methanogenesis
D) transformed, along with other ions, into inorganic compounds

Question 10

How do arbuscular mycorrhizae (AM) help plants obtain more nutrients from the soil?

A) Signaling molecules in the plant are passed to the AM to initiate electron flow, which is in turn used to create ATP.
B) The hyphae develop as specialized nodules that directly produce nutrients for the plant.
C) Byproducts of AM metabolism serve as primary nutrient sources for the plants.
D) The AM increase the total surface area to absorb more nutrients.

Question 11

Most nitrogen- fixing bacteria symbiotically associated with plants are called

A) bacteroids.
B) symbiodinia.
C) mycorrhizae.
D) rhizobia.

Question 12

The mutualism of Azolla- Anabaena is useful for

A) corn farmers.
B) aquaculturalists.
C) rice farmers.
D) tropical forest community succession.

Question 13

What volume is the rumen in cows?

A) 25-50 liters
B) 100-150 liters
C) 10-20 liters
D) 5-10 liters

Question 14

The function of leghemoglobin in root nodules is to

A) chelate iron.
B) produce iron.
C) produce nitrogen.
D) bind oxygen.

Question 15

Plant root nodules are

A) structures created by fungi and are found in all agricultural crops.
B) formed from gall- rotting bacteria that decompose plant roots.
C) harmful to plants, because the bacteria outcompete the plants for nutrients.
D) sites where nitrogen fixation occurs.

Question 16

What proportion of insects are thought to have symbiotic relationships with microorganisms?

A) 5%
B) less than 1%
C) 20%
D) 50%

Question 17

What percentage of terrestrial plants are colonized by arbuscular mycorrhizae?

A) 25
B) 85
C) 50
D) 10

Question 18

Which bacterial genus can sterilize male insect sperm?

A) Wolbachia
B) Allivibrio
C) Symbiodinium
D) Buchnera

Question 19

Two organisms that both benefit from each other are in a symbiotic relationship called

A) commensalism.
B) parasitism.
C) ammensalism.
D) mutualism.

Question 20

Ruminants digest bacterial cells as a primary source of

A) carbohydrates.
B) lipids.
C) vitamins.
D) proteins.

Question 21

The specificity of certain rhizobia to infect only particular plants is in part due to the

A) nod genes they possess.
B) abundance of nutrients present in the soil.
C) season (time of year).
D) rhizobial lipids that act as signaling molecules.

Question 22

Bacterial symbionts most often provide insects with _ that are essential for their growth.

Question 23

Which of the following is NOT a major question in the Human Microbiome Project?

A) Do differences in the human microbiome correlate with differences in human health?
B) How is the microbiome developed after an individual is born?
C) Are differences in the relative abundance of different bacteria important?
D) Is there a correlation between microbial population structure and host genotype?

Question 24

What is the result of calcium carbonate skeleton corals collecting solar radiation?

A) Calcium and carbonate ions are released, which help buffer the pH and prevent dramatic pH shifts.
B) The incident light field is amplified five times that of solar light, which fosters growth of phototrophic dinoflagellates.
C) Speciation is induced due to mutation rates of the bacteria associated with the corals being high.
D) The water's temperature around the coral is much warmer.

Question 25

Nearly all animals lack the ability to catabolize plant fibers, however of the polysaccharides in plants that is mediated by provides usable carbon and energy substrates for animals.

Question 26

is a process in symbiosis where both organisms' genomes change over time in a reciprocal fashion.

Question 27

are intracellular bacteria that are usually localized to specialized organs within their host.

Question 28

Which two phyla dominate the Bacteria in the rumen?

A) Actinobacteria and Proteobacteria
B) Firmicutes and Proteobacteria
C) Bacteriodetes and Proteobacteria
D) Bacteriodetes and Firmicutes

Question 29

Which of the following is a common feature of primary symbionts?

A) high A+T content, low G+C content
B) accelerated mutation rates
C) extreme genome reduction
D) all of the above

Question 30

Compared to carnivorous organisms, herbivores have an extended retention time of food
in their gut, which benefits the organisms by .

Question 31

Gut symbionts such as Aeromonas veronii of leeches are environmentally transmitted by

A) their food being infected by the bacterium.
B) water containing the motile bacterium.
C) exposure to infected biofilms.
D) developing within infected cocoons.

Question 32

Aphids that feed on carbohydrate rich but nutrient poor foods obtain many from
Buchnera.

Question 33

The primary site(s) of fiber breakdown mediated by microorganisms in cecal fermenters is/are , and the site(s) for hindgut fermenters is/are .

Question 34

In a consortium, green sulfur bacteria that surround and attach to a flagellated bacterium are called

A) exobionts.
B) saprophytes.
C) epiphytes.
D) holobionts.

Question 35

During the Jurassic Period, several different mammalian lineages independently evolved a(n) lifestyle for obtaining energy.

Question 36

What is the role of the vir genes on a Ti plasmid?

A) replication of the plasmid
B) cause crow gall disease (virulence)
C) T- DNA transfer
D) conferring resistance to viral infection

Question 37

The activity of can be assayed by the reduction of acetylene into ethylene.

Question 38

The microbiome contains all

A) living organisms present on the skin.
B) organisms present in and on the body.
C) viable cells in a particular location.
D) organisms within the digestive system.

Question 39

Where are ectomycorrhizae most commonly found?

A) tropical forests
B) forests with especially low nutrients
C) boreal and temperate forests
D) all of the above

Question 40

The moonlight- like _ from Allivibrio fischeri are symbionts of the Hawaiian bobtail
squid, which benefits from evading

Question 41

The formation of rhizobial nodules is induced by _ .

Question 42

The structural and trophic foundation of coral reefs is a mutualistic relationship between
and .

Question 43

Coral bleaching has been primarily caused by antimicrobials that have disrupted the mutualistic relationships formed with other corals that depend on microbial symbionts for essential nutrients.

Question 44

Microbial symbionts are horizontally transferred by parental cells directly passing on the symbionts during cellular replication.

Question 45

Leguminous plants such as alfalfa, beans, clover, peas, and soybeans all benefit from symbiotic bacteria that leach vitamins into the plant roots.

Question 46

Gut symbionts are lost after each molting an insect undergoes.

Question 47

A consortium's species name is in _ , because each consortium is not actually
.

Question 48

Certain species of Bacteria have been identified to cause obesity.

Question 49

Archaea are commonly present in rumens.

Question 50

A prolonged and intimate relationship between two organisms that evolved as they lived together is called .

Question 51

While rhizobia usually associate with plant roots, nodules can also be formed along the stems of leguminous plants.

Question 52

Fungal cells that form an extensive sheath around the outside of the root but only make slight penetrations into the root tissue are called _ _, while those that are deeply embedded into root tissue are called .

Question 53

Microorganisms can associate with and benefit plants by increasing and defending against _ _.

Question 54

Symbiotic relationships generally do not foster horizontal gene transfer at any higher rate than non- symbiotic relationships.

Question 55

Plant diversity is generally lower in environments where mycorrhizae are associated with them due to strong coevolution, which drives the fungus- plant relationship to diverge.

Question 56

Regarding the human oral flora, Streptococcus primarily colonize , while
Fusobacterium and Veillonella colonize _ _.

Question 57

The most heavily colonized human organ by bacteria is the , containing 1011
-10¹² bacterial cells per g.

Question 58

An individual tree can maintain a symbiotic relationship with many different species of mycorrhizae simultaneously.

Question 59

Leeches such as Hirudo verbana are capable of consuming five times the amount of blood than its own bodyweight.

Question 60

Both pathogenic bacteria and primary symbionts have a tendency to lose genes for catabolic pathways.

Question 61

The gut flora is relatively stable over long time periods in healthy adults, suggesting its "fine- tuned" role.

Question 62

Bacterial cells themselves serve as major sources of protein and vitamins in hindgut fermenting animals.

Question 63

The bacterium Escherichia coli comprises a significant fraction of the bacterial population in healthy adult humans, ranging from 10-50%.

Question 64

The reproductive systems of many insects can be manipulated by parasitic symbionts, which are passed down to each generation and can skew the sex ratio of their progeny.

Question 65

Provide a biochemical explanation of why a cow might eructate (belch).

Question 66

Hydrogenosomes present in some anaerobic protists have yet to be identified in any other taxonomic group.

Question 67

Describe a way in which Hawaiian bobtail squids exclude all bacteria except Allivibrio fischeri into their light organ. Also explain how A. fischeri is capable of colonizing the organ.

Question 68

Due to the close interactions with other organisms, microbial symbionts generally have larger genome sizes compared to other non- symbiotic bacteria.

Question 69

Provide an example of how an abrupt diet change in a rumen such as a cow can cause serious illnesses, even death. Also explain the processes that develop into sickness.

Question 70

According to the free energy obtained from each product using CO2 and H2, methanogenesis is favored over acetogenesis. Why is this NOT the case in termites?

Question 71

The mycelia of mycorrhizae can form underground nutrient networks where several trees are connected.

Question 72

Molecular evidence suggests that leeches contain four distinct bacterial communities in its digestive tract.

Question 73

Explain the role of the Ti plasmid in causing crown gall disease in plants.

Question 74

Explain how leeches are used today in medical replants and transplants.

Question 75

Two- thirds of terrestrial environments support growth of termites.

Question 76

How do arbuscular mycorrhizae colonize roots?

Question 77

Several rhizobial species within a cross- inoculation group should be able to grow with particular legume species such as alfalfa, however the same cross- inoculation group would be unable to associate with other legumes species.

Question 78

Bacteroids are rarely found within plant cells.

Question 79

Biogeography studies have identified 16S rRNA genes of green bacterial consortia from nearby lakes containing identical sequences.

Question 80

Bacteria associated with plants fix approximately 25% of all nitrogen fixed annually on Earth.