Chapter 27: Microbial Interactions

Question 1

Many Types of Microbial Interactions Exist

Microbial Interactions

(1)—stable association of two or more organisms (host and (2)).
* Beneficial, neutral or negative impact.

(3)—alternative lifestyle possible.
(4)—host is absolutely required.

Answer 1

1. Symbiosis
2. symbiont
3. Facultative
4. Obligatory

Question 2

Microbial Interaction Categories

(1)—both partners benefit from each other.
* In many cases, this is an obligatory relationship.

(2)—nonobligatory.
* Difficult to distinguish from mutualism because the organisms may be able to live in different environments.

(3)—one organism negatively impacts another.

Answer 2

1. Mutualism
2. Cooperation
3. Antagonism

Question 3

Mutualism: Obligatory Positive Interaction

(1)
When one species benefits from the metabolic products of another.

(2)
* The removal of (3) from the environment, enabling fermentations that are thermodynamically unfavorable.
* (4) found in this association

Answer 3

1. Syntrophy
2. Interspecies hydrogen transfer
3. H2
4. Methanogenic archaea

Question 4

Microorganism-Insect Mutualisms

B. aphidicola and aphids
* (1)—lives (2) its host cells.
* Mature aphid contains millions of these bacteria within (3).
* Microbes live in a secure habitat, and host gets amino acids absent in spp.

• (4)—evolved together because both partners cannot grow
  without each other.

Answer 4

1. Endosymbiont
2. within
3. bacteriocytes
4. Coevolution

Question 5

Termite-Associated Protists

Termites feed on only wood, made of cellulose and lignocellulose.
* Termites make (1).
* Only (2) can complete lignocellulose degradation.
Often in (3) clade.

Trichonympha sp. relies on a (4) in the genus Elusimicrobium to convert glutamine to amino acids and nitrogenous compounds.

Answer 5

1. own cellulolytic enzyme
2. mutualistic protists
3. metamonada
4. bacterial endosymbiont

Question 6

Mutualisms with Primary Producers

(1)—capture energy from a nonliving source.
(2)—CO2 is sole carbon source.
Reaction fuel.
* (3)—photosynthetic processes.
* (4)—uses reduced, inorganic chemicals as electron
source.

Answer 6

1. Primary producers
2. Autotrophs
3. Phototrophy
4. Lithotrophy

Question 7

Coral Holobiont

Marine invertebrates harbor endosymbiotic (1).

Hermatypic corals get energy using photosynthetic (2).
* Protist that (3) give 95% of fixed-carbon in exchange for nitrogenous compounds.

Answer 7

1. photosynthetic dinoflagellates
2. Symbiodinium
3. line coral gastrodermis

Question 8

Coral Bleaching

Loss of either the (1) or the (2) from the coral.
* Caused by (3)

During and following bleaching, the microbial community is in (4) and stressed corals are susceptible to pathogens.
* White plague and yellow blotch disease kill Caribbean corals.

Answer 8

1. photosynthetic pigments from the dinoflagellates
2. complete expulsion of the dinoflagellates
3. temperature increase
4. disequilibrium

Question 9

Tube Worm Holobiont

(1)
* Exist thousands of meters below ocean surface.
* Tube worms (that is, Riftia) at vents are (2) with bacterial endosymbionts.
* Worm lacks digestive tract and relies on bacteria to (3).
* Bacteria get convenient delivery of (4).

Answer 9

1. Hydrothermal vent community
2. mutualistic
3. provide organic carbon
4. carbon source, electron donor and acceptor

Question 10

The Rumen Ecosystem

Ruminants
* Animals that have stomach divided into (1) and chew a (2).

(3)
* Upper part of the ruminant stomach.
* Contains large, diverse population of microbes.

Answer 10

1. four compartments
2. cud
3. Rumen

Question 11

Ruminants

Ruminants and microbial community have a mutualistic relationship.
Microbes in rumen carry out (1).
The animal consumes complex plants; therefore, (2) require multiple enzymes.
* Community of microbes act together to make these enzymes.

Answer 11

1. anaerobic metabolism
2. hydrolysis of simple carbohydrates

Question 12

Cooperation: Nonobligatory Positive Interactions

Cooperation
Differs from mutualism because cooperative relationship is (1).

X. nematophila and nematode host.
* Bacteria contributes to (2).

Answer 12

1. not obligatory
2. reproductive success

Question 13

Fungal Highway

• Physical network of fungal hyphae that promote (1).
• Spread on solid surfaces, growing towards nutrients.
• Bacteria move along (2) to explore new environments.

Answer 13

1. bacterial dispersal
2. hyphal surface

Question 14

Lichens

Association between (1).

(2)—fungal partner.
* Provides water, minerals, and firm substratum for growth.
(3)—alga or cyanobacterial partner.
* Provides oxygen.

Answer 14

1. fungi and green algae
2. Mycobiont
3. Photobiont

Question 15

Antagonistic Interactions Prompt Microbial

Responses

Antagonistic Interactions

(1)—killing
* Benefit after the victim is killed.

(2)—exploitation
* Benefit while the victim is alive.

(3)
* Uneasy truce between microbes.

Answer 15

1. Predation
2. Parasitism
3. Competition

Question 16

Microbes Overcome Viruses

(1)
* Chemically distinguish viral and host DNA and hydrolyze viral DNA.

(2)
* Recognize viral DNA by comparing samples from previous encounters to identify and degrade viral genomes.

Viruses have developed strategies to get around these host
defenses.

Answer 16

1. Restriction-modification
2. CRISPR/Cas system

Question 17

Protozoans: Predators of Bacteria

(1)—process by which protozoans consume bacteria.
* Transfers (2) from bacteria to more complex organisms.
* Bacteria defensive mechanisms to avoid consumption:
– (3)
– (4)

Answer 17

1. Grazing
2. carbon and energy
3. Grow larger
4. Form biofilms

Question 18

Predation Strategies

• (1) predators—attach to prey’s surface and lyse to release prey’s cytoplasmic contents.
• (2) predators—invade victim’s cytoplasm where they consume contents to get energy.

Answer 18

1. Epibiotic
2. Endobiotic

Question 19

Predation By Myxococcus Xanthus

Myxococcus is a (1) predator.
* Consumes organic matter released from (2).
Use gliding motility to creep toward prey while releasing (3).

Answer 19

1. facultative
2. dead organisms
3. degradative enzymes

Question 20

Parasitism

Parasite and host (1).
* Can involve nutrient acquisition, physical maintenance, or
both.
* If equilibrium is (2), one organism may die.
(3) common in symbiotic relationships.
* Discard (4).
* Occurs when symbiont has become (5).

Answer 20

1. coexist
2. shifted
3. Genomic reduction
4. unused genetic information
5. dependent on host for specific functions

Question 21

Competition

Arises when different organisms
within a community try to
(1).

Two possible outcomes of
competition:
* (2)—via antibiotics.
* (3)—physical proximity required for toxin delivery.

Answer 21

1. acquire the same resource
2. Contact-independent growth inhibition
3. Contact-dependent growth inhibition