MCB122 Symbioses1

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

A) ammensalism.

B) commensalism.

C) mutualism.

D) parasitism

C) mutualism.

2) 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.

A) Wolbachia supplies essential nutrients to the mosquito Culex quinquefasciatus.

3) Most nitrogen-fixing bacteria symbiotically associated with plants are called

A) bacteroids.

B) mycorrhizae.

C) rhizobia.

D) symbiodinia.

C) rhizobia.

4) 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

C) sites where nitrogen fixation occurs.

5) The function of leghemoglobin in root nodules is to

A) bind oxygen.

B) chelate iron.

C) produce iron.

D) produce nitrogen.

A) bind oxygen.

6) 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

C) cell morphology

7) 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).

C) rhizobial lipids that act as signaling molecules.

8) The mutualism of Azolla-Anabaena is useful for

A) aquaculturalists.

B) corn farmers.

C) rice farmers.

D) tropical forest community succession.

C) rice farmers.

9) 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

B) Agrobacterium tumefaciens

10) 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

D) T-DNA transfer

11) 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

A) boreal and temperate forests

12) 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.

B) The AM increase the total surface area to absorb more nutrients.

13) 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

D) anaerobic / cellulolytic and fermentative bacteria

14) 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

B) acetic, butyric, and propionic acids

15) 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.

B) produce more volatile fatty acids by fermentation.

16) 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.

C) organisms present in and on the body.

17) 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?

D) How can we reduce the number of microbes on the human body?

18) 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

C) required for host reproduction / are not required for host reproduction

19) 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

D) has been observed, but is considered a rare event

20) 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

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

21) 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.

B) nitrogen metabolism.

22) 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

A) vertically to offspring

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

A) clams

B) corals

C) flatworms

D) snails

B) corals

24) 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

C) The coral skeleton is an extremely efficient light-gathering structure that greatly enhances light harvesting for photosynthesis.

25) Ruminants digest bacterial cells as a primary source of

A) carbohydrates.

B) vitamins and proteins.

C) proteins.

D) vitamins.

B) vitamins and proteins.

26) Two main symbionts of termites are ________ and ________.

A) archaea / bacteria

B) bacteria / fungi

C) bacteria / protists

D) fungi / protists

C) bacteria / protists

27) What percentage of terrestrial plants are colonized by arbuscular mycorrhizae?

A) 10

B) 25

C) 50

D) 85

D) 85

28) 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.

D) It is used in methanogenesis.

29) 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.

A) The population size is low, but diversity is high.

30) 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.

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.

31) 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

A) coevolution

32) 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.

B) horizontal and involves specific selection of the symbiont from the environment.

33) 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

D) increased nutrient availability and decreased pathogen colonization

34) 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

A) They both use lipochitin oligosaccharide signaling factors to initiate root colonization.

35) 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

D) nod genes

36) 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

A) they cannot be maintained in pure culture.

37) 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.

B) different digestive patterns in herbivorous animals that all depend on gut microbiota to digest plant material.

38) 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.

A) the plant supplies carbohydrates to the fungus and the fungus supplies phosphorus and nitrogen to the plant.

39) 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

C) large intestine

40) 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.

B) diverse aerobic and anaerobic microorganisms.

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

A) Symbiodinium

B) Arbuscules

C) Epibionts

D) Endosymbionts

D) Endosymbionts

42) 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

A) the fungus protects the photosynthetic partner from erosion.

43) 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

B) amino acids

44) 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.

A) mimicking the light of the moon, which helps the squid avoid nocturnal predators.

45) 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)

C) dinoflagellates and stony corals (Cnidaria).

46) 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

D) fixed carbon dioxide in the form of organic compounds

47) 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.

A) H2S and O2 in order to transport these chemicals to their bacterial symbionts.

48) 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

C) iron and trace metal absorption

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

True

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

False

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

False

4) 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

True

5) Bacteroids are rarely found within plant cells

False

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

True

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

True

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

True

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

False

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

False

11) Archaea are commonly present in rumens

True

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

True

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

False

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

True

15) Certain species of Bacteria have been identified to cause obesity.

False

16) 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.

True

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

False

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

False

19) Two-thirds of terrestrial environments support growth of termites

True

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

False

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

False

23) Biofilms in the human mouth primarily contain pathogens.

False

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

True

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

False

20) Gut symbionts are lost after each molting a termite undergoes.

True