Deck 22: Microbial Symbioses

Question 1

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

A)accelerated mutation rates
B)extreme genome reduction
C)high A+T / low G+C content
D)accelerated mutation rates,extreme genome reduction,and high A+T / low G+C content

Answer 1

D

Question 2

Weight gain and obesity may be partly caused by certain gut microbial communities that

A)absorb more vitamins and essential amino acids.
B)produce more volatile fatty acids by fermentation.
C)stimulate the gut endothelium to absorb more sugars.
D)produce more hydrogen gas by fermentation.

Answer 2

B

Question 3

In insects,primary symbionts are ________,while secondary symbionts ________.

A)heritable / are transmitted horizontally
B)able to replicate outside of the host / are obligate symbionts
C)required for host reproduction / are not required for host reproduction
D)obligate symbionts / have a free-living replicative stage

Answer 3

C

Question 4

The microbiome contains all

A)organisms present on the skin.
B)organisms within the digestive system.
C)organisms present in and on the body.
D)organisms present on the skin and in the digestive system.

Question 5

The insect symbiont Wolbachia can be used to suppress disease transmission by mosquitoes because

A)Wolbachia supplies essential nutrients to the mosquito Culex quinquefasciatus.
B)only Wolbachia-infected mosquitoes can transmit viral diseases such as dengue fever.
C)Wolbachia infections can spread rapidly through a mosquito population,killing all the mosquitoes.
D)Wolbachia-infected male mosquitoes sterilize uninfected female mosquitoes.

Question 6

The rumen is an ________ habitat that depends on ________ to digest cellulose for ruminant animals.

A)aerobic / cellulolytic fungi
B)aerobic / cellulolytic and fermentative bacteria
C)anaerobic / methanogens
D)anaerobic / cellulolytic and fermentative bacteria

Question 7

The mutualism of Azolla-Anabaena is useful for

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

Question 8

Which compounds serve as major sources of energy for ruminant animals?

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

Question 9

The function of leghemoglobin in root nodules is to

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

Question 10

Where are ectomycorrhizae MOST commonly found?

A)boreal and temperate forests
B)forests with especially low nutrients
C)tropical forests
D)boreal and temperate forests,forests with especially low nutrients,and tropical forests

Question 11

Horizontal gene transfer between host organisms and their symbionts

A)happens frequently because of coevolution.
B)causes genome reduction in the symbiont and genome expansion in the host.
C)causes genome reduction in both the host and the symbiont.
D)has been observed,but is considered a rare event.

Question 12

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

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

Question 13

Most nitrogen-fixing bacteria symbiotically associated with plants are called

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

Question 14

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

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

Question 15

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

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

Question 16

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

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

Question 17

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

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

Question 18

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

A)Are differences in the relative abundance of different bacteria important?
B)Do differences in the human microbiome correlate with differences in human health?
C)Is there a correlation between microbial population structure and host genotype?
D)How can we reduce the number of microbes on the human body?

Question 19

Plant root nodules are

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

Question 20

How is a bacteroid distinguished from a bacterial cell?

A)16S rRNA gene sequencing
B)biochemical tests
C)cell morphology
D)16S rRNA gene sequencing,biochemical tests,and cell morphology

Question 21

The signaling factors of arbuscular mycorrhizae most likely gave rise to the signaling factors used in rhizobial nodule formation,yet less is known about arbuscular mycorrhizae because

A)they cannot be maintained in pure culture.
B)they are not as important for plant health.
C)no genetic systems have been developed for fungi.
D)they are not as important for plant health and no genetic systems have been developed for fungi.

Question 22

Ruminants digest bacterial cells as a primary source of

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

Question 23

A species of insect that lives solely on pine sap was found to contain a bacterial symbiont.Genome sequencing of both the host and the symbiont revealed that the symbiont lacked many genes required for energy production,and the host lacked genes for biosynthesis of several essential amino acids.What is/are the most likely mechanism(s)that caused the loss of these genes?

A)coevolution
B)horizontal gene transfer
C)increased mutation rate
D)horizontal gene transfer and increased mutation rate

Question 24

During the Jurassic Period,several different mammalian lineages independently evolved an herbivorous lifestyle for obtaining energy.This has resulted in

A)different digestive patterns in herbivorous animals,some that depend on gut microbiota to digest plant material and some that do not.
B)different digestive patterns in herbivorous animals that all depend on gut microbiota to digest plant material.
C)the evolution of foregut fermentation,as seen in ruminants,as the only digestive pattern that depends on fermentative gut microbiota.
D)horizontal gene transfer of genes for glycoside hydrolases and polysaccharide lyases from bacteria to mammals.

Question 25

The human oral flora consists of

A)a small group of phylogenetically related aerobic microorganisms.
B)diverse aerobic and anaerobic microorganisms.
C)monoculture biofilms on tooth surfaces.
D)the same phyla that are found in the human gut.

Question 26

In mycorrhizal mutualisms between plants roots and fungi,

A)the plant supplies carbohydrates to the fungus and the fungus supplies phosphorus and nitrogen to the plant.
B)the plant supplies water to the fungus and the fungus supplies essential amino acids to the plant.
C)the plant protects the fungus from predation and the fungus supplies carbohydrates to the plant.
D)the fungus infects the plant roots,stimulating plant growth through myc factors that act as growth hormones in the plant.

Question 27

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

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

Question 28

How do phototrophic microorganisms benefit when associating with corals?

A)Calcium and carbonate ions are released,which help buffer the pH and prevent dramatic pH shifts.
B)The coral skeleton is used as a source of bicarbonate for the autotrophic growth of the phototrophs.
C)The coral skeleton is an extremely efficient light-gathering structure that greatly enhances light harvesting for photosynthesis.
D)The water's temperature in and around the coral skeleton is much warmer.

Question 29

What percentage of terrestrial plants are colonized by arbuscular mycorrhizae?

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

Question 30

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

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

Question 31

How are root nodule and arbuscular mycorrhizal symbioses similar?

A)They both use lipochitin oligosaccharide signaling factors to initiate root colonization.
B)They both supply nitrogen to the host plant through nitrogen fixation.
C)They both increase absorption of nutrients from soil.
D)They are both required for the growth and reproduction of their host plants.

Question 32

What is the fate of H₂ produced within a rumen?

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

Question 33

Symbionts such as Aeromonas veronii of leeches and Buchnera symbionts of insects are transmitted ________ to ensure the safe transfer of the symbiont to the next host generation.

A)vertically to offspring
B)horizontally through infected water
C)horizontally through infected secondary hosts
D)vertically through the air

Question 34

Bacterial symbionts of termite hindguts play a critical role in the termite's

A)reproduction.
B)nitrogen metabolism.
C)resistance to fungal infection.
D)reproduction and nitrogen metabolism.

Question 35

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

A)mouth
B)small intestine
C)large intestine
D)skin

Question 36

When the squid that contain luminescent bacterial symbionts hatch,they do NOT contain a bacterial symbiont.Symbiont transmission in this symbiosis is

A)vertical from parent to offspring.
B)horizontal and involves specific selection of the symbiont from the environment.
C)random and results in various different species being selected as the symbiont.
D)mixed and results in multiple symbiont species colonizing the squid at once.

Question 37

Which of the following is a common benefit of a microbe-plant symbiosis?

A)increased nutrient availability
B)decreased pathogen colonization
C)increased affinity for carbon dioxide
D)increased nutrient availability and decreased pathogen colonization

Question 38

Two main symbionts of termites are ________ and ________.

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

Question 39

A mutant of Rhizobium leguminosarum is able to survive and reproduce in the laboratory outside of plant roots,but can no longer initiate root nodule formation.What type of genes are most likely mutated in this mutant?

A)rhz genes
B)myc genes
C)nif genes
D)nod genes

Question 40

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

A)Ancestral symbionts had low GC content genomes by chance,and these low GC content genomes are passed onto their progeny.
B)Free-living organisms must have a more stable genome to survive; low G+C content organisms are often selected against in nature.
C)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.
D)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.

Question 41

Archaea are commonly present in rumens.

Question 42

Bacteria associated with plants fix very small amounts of nitrogen,therefore they do NOT contribute significantly to the global N cycle.

Question 43

Allivibrio fischeri symbionts benefit the Hawaiian bobtail squid by

A)mimicking the light of the moon,which helps the squid avoid nocturnal predators.
B)providing essential amino acids missing from the squid's diet.
C)degrading the cellulosic cell walls of the phytoplankton the squid eats.
D)providing essential amino acids missing from the squid's diet and degrading the cellulosic cell walls of the phytoplankton the squid eats.

Question 44

Consortia of a phototrophic green sulfur bacteria and motile heterotrophs are found worldwide in freshwater stratified sulfidic lakes.

Question 45

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

Question 46

Aphids that feed on carbohydrate-rich but nutrient-poor foods obtain________ from their endosymbiotic bacterial partners.

A)ATP
B)amino acids
C)ammonium
D)volatile fatty acids

Question 47

Plant diversity is generally lower in environments where mycorrhizae are associated with plants due to strong coevolution,which leads to competitive exclusion.

Question 48

Bacterial symbionts most often provide marine invertebrates with

A)fixed nitrogen in the form of ammonia.
B)essential amino acids missing from the animal's diet.
C)cellulolytic enzymes to help digest plant material.
D)fixed carbon dioxide in the form of organic compounds.

Question 49

Lichens are a mutualistic association of a fungus and either an alga or a cyanobacterium in which

A)the fungus protects the photosynthetic partner from erosion.
B)the fungus slowly engulfs the photosynthetic partner.
C)the fungus helps collect sunlight for the photosynthetic partner.
D)the phototroph provides phosphorus to the fungus.

Question 50

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

Question 51

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

Question 52

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

Question 53

Bacteroids are rarely found within plant cells.

Question 54

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

Question 55

Which of the following is NOT a function of the human gut microbiome?

A)production of essential amino acids and vitamins
B)production of volatile fatty acids from polysaccharides
C)iron and trace metal absorption
D)maturation of the gastrointestinal tract

Question 56

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

A)Symbiodinium
B)Arbuscules
C)Epibionts
D)Endosymbionts

Question 57

Riftia tube worms contain unusual hemoglobins that bind(s)

A)H₂S and O₂ in order to transport these chemicals to their bacterial symbionts.
B)high concentrations of O₂ produced by their photosynthetic symbionts.
C)sulfate to transport this ion away from their bacterial symbionts.
D)ammonia that their bacterial symbionts produce.

Question 58

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

A)cyanobacteria and sponges (Porifera).
B)chemolithotrophic bacteria and stony corals (Cnidaria).
C)dinoflagellates and stony corals (Cnidaria).
D)cyanobacteria and stony corals (Cnidaria).

Question 59

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 another legume species such as peas.

Question 60

Fungi and protists serve an important role in the anaerobic digestion of cellulose in ruminants.

Question 61

Gut symbionts are lost after each molting a termite undergoes.

Question 62

Molecular evidence suggests that leeches contain two distinct bacterial communities in their bladder.

Question 63

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

Question 64

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

Question 65

How do Hawaiian bobtail squids prevent all bacteria except Allivibrio fischeri from colonizing their light organ?

Question 66

What is the difference between a primary and secondary insect symbiont? Propose how you might use an insect symbiont to control the spread of an insect-borne disease.

Question 67

The gut flora is relatively stable over long time periods in healthy adults,suggesting its highly evolved role in the human body.

Question 68

Two-thirds of terrestrial environments support growth of termites.

Question 69

Genome sequencing of the bacterial symbionts of animals has allowed us to compare the genomic features of several symbionts.The following data were collected on two insect symbionts:
Symbiont A: 0.4 Mb genome,20% G+C content,missing or incomplete peptidoglycan synthesis and nucleotide synthesis pathways.
Symbiont B: 1.8 Mb genome,40% G+C content,peptidoglycan and most nucleotide synthesis pathways complete.
What can you deduce about these two insect symbionts based on their genomes?

Question 70

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

Question 71

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 72

Describe the mutualistic relationship between chemolithotrophic bacteria and tube worms in hydrothermal vents.

Question 73

Biofilms in the human mouth primarily contain pathogens.

Question 74

Both lichens and corals are symbioses involving phototrophic microorganisms.Compare and contrast lichens and corals,including the types of organisms involved,the role of each partner,the specificity of the interaction,and the method of transmission for each symbiosis.

Question 75

Certain species of Bacteria have been identified to cause obesity.

Question 76

The following quote is taken from a university extension publication for farmers:
"Grain poisoning,also known as grain overload or lactic acidosis,is usually the result of stock consuming large quantities of grain or pellets to which they are unaccustomed.Pasture-fed cows or feedlot cattle not yet adapted to grain may become acutely ill or die after eating only moderate amounts of grain,whereas stock accustomed to diets high in grain content may consume large amounts of grain with little or no effect."
What is happening in the digestive system of the livestock that causes grain poisoning and why does a gradual shift in diet avoid this problem?

Question 77

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

Question 78

Why was Escherichia coli thought to be a dominant member of the human gut microbial community in the past? What populations ARE important in the human gut and what evidence do we have that the specific bacteria present are important for human health?

Question 79

Coral bleaching is primarily caused by antimicrobials that disrupt the mutualistic relationships formed between corals and their bacterial symbionts.

Question 80

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