chapter 23 - microbial symbioses

Question 1

What is symbiosis?

Answer 1

close, prolonged association between two or more organisms from different species

Question 2

What is mutualism?

Answer 2

relationship where both organisms interact to the benefit of both; most mutualistic organisms have coevolved over millions of years

Question 3

What is commensalism?

Answer 3

relationship where an organism benefits and the other is not significantly harmed or helped.

Question 4

What is parasitism?

Answer 4

relationship where the parasite benefits while the host is harmed.

Question 5

What are lichens?

Answer 5

mutualistic relationship between a fungus and an alga
(alga provides carbohydrates for the fungus, fungus gives structure to alga)

Question 6

What is methanotrophic consortia?

Answer 6

couple the activities of two anaerobes to effectively oxidizing methane to carbon dioxide in anoxic marine sediments.

Question 7

What are nanowires?

Answer 7

direct interspecies electron transfers

Question 8

What are legumes?

Answer 8

plants with seeds in pods (soybeans, peas)

Question 9

What are Rhizobia?

Answer 9

best known nitrogen-fixing bacteria engaged in legume-root nodule symbioses

Question 10

What are cross-inoculation groups?

Answer 10

group of related legumes that can be infected by a particular species of rhizobia

Question 11

What are nitrogenase?

Answer 11

enzyme that fixes nitrogen are inactivated by high oxygen level

Question 12

What are leghemoglobin?

Answer 12

they bind oxygen, they are redish in color, as they have an iron group. The part of the nodule is red and the other part green, allowing binding. It also protects nitrogenase from free oxygen.

Question 13

What is an infection thread?

Answer 13

a cellulosic tube formed by the plant induced by the bacterium that spreads down the root hair.

Question 14

What is the biochemistry of root nodules?

Answer 14

infection thread allows bacteria to enter into the plant. They go inside and form symbiosomes, where they change shape.

sugar is broken down to 4 carbon organic acid which feeds into the citric acid cycle and then electrons fo through electron transport chain, driving ATP.

Question 15

What is mycorrhizae?

Answer 15

mutualisms between plant roots and fungi.

Question 16

What is ectomycorrhizae?

Answer 16

fungus remains outside the plant roots.
fungal cells form a sheath around the outside of the root with only a small penetration into the root tissue.

Question 17

What is endomycorrhizae?

Answer 17

fungal mycelium becomes deeply embed with the root tissues.
It cannot be cultured in pure culture

Question 18

What is the arbuscular mycorrhizal root colonization?

Answer 18

1- plant roots release hormone stimulating growth of root systems and germination of fungal spores.
2- fungi produce oligosaccharide signaling molecules to initiate formation of the mycorrhizal state
3- fungal mycelium forms an attachment structure and can penetrate through epidermal cells and cells of outer cortex.

Question 19

How can microbial symbionts be acquired?

Answer 19

1. environmental reservoirs (horizontal transmission)
2. Parent (heritable transmission)

Question 20

What are the two different types of symbionts of insects?

Answer 20

1. primary symbionts - required for host reproduction
2. secondary symbionts - not required for host reproductions

Question 21

What are the characteristics of primary symbionts?

Answer 21

1- found in several insect groups
2- restricted to specialized region of the host called bacteriome
3- within the bacteriome, bacterial cells reside in specialized cells called bacteriocytes