Lecture 16

Question 1

What bacteria are found in soil?

Answer 1

proteobacteria dominate, acidobacteria, actinobacteria

Question 2

Rhizosphere

Answer 2

volume of soil around plant roots influenced by materials released from roots. zone of chemical, biological, and physical influence generated by root growth and activity

Question 3

Rhizoplane

Answer 3

surface of root, including soil particles

Question 4

Mycorrhizal symbiosis

Answer 4

fungal symbiosis helps plants acquire phosphate and nitrogen from the soil

Question 5

Rhizobial symbiosis

Answer 5

Bacterial symbiosis helps plants acquire nitrogen from the atmosphere

Question 6

Lineages of proteobacterium

Answer 6

gram -, alphaproteobacterium, betaproteobacterium, gammaproteobacterium, deltaproteobacterium, epsilonproteobacterium

Question 7

Class alphaproteobacteria

Answer 7

7 orders, 20 families, gram -, live in environments typically low in nutrients (oligotrophic), most abundant bacteria in oceans

Question 8

Rhizobia

Answer 8

microbial genera able to form nitrogen fixing nodules with legumes, free in soil but cannot fix nitrogen under aerobic conditions

Question 9

Atmosphere composition (nitrogen fixation)

Answer 9

nitrogen (most abundant), nitrogen fixation = conversion of N2 in ammonia, carried out by only some soil bacteria

Question 10

Legume-rhizobia symbiosis

Answer 10

nitrogen is limiting in some soils
1. rhizophere communication - legume <> rhizobia
2. Endosymbiosis - rhizobia enter inside plant cells
3. Legumes: fabales (fabaceae) inhabit nitrogen poor soils

Question 11

Biological nitrogen fixation - fossil fuel free

Answer 11

• rhizobia contain nitrogenase, fixation of N2 demanding, inhibited by oxygen, free rhizobia do not fix N in soil, nodules provide microaerobic environment

Question 12

Global nitrogen fertilizer production (Haber)

Answer 12

N2 + 3H2 <> 2NH3
2% of global ff comsumption, sustains 1/3 of global pop. 1/2 nitrogen in human body from N fertilizer

Question 13

Nitrogen fertilizer run off

Answer 13

20% of N is lost as run off in lakes + rivers, eutrophication leads to oxygen depletion

Question 14

Flavonoids

Answer 14

Secreted by legume roots into the soil when nitrogen levels are low

Question 15

Nodulation factor

Answer 15

produced by rhizobia to gain entry into legume roots (LCO)

Question 16

Legume Rhizobium communication (3 steps)

Answer 16

1. plant roots exude flavonoids into the soil when N levels low
2. Rhizobia perceive flavonoids indicates that a root is nearby
3. Rhizobia in turn produce nod factor (LCO)

Question 17

Root nodule formation by rhizobium

Answer 17

1. perception of nod factor by plant triggers changes in root hairs to allow rhizobia to enter
2. plant builds infection thread to guide rhizobia into inner tissues
3. surrounded by peribacteroid membrane, units now called symbiosomes. then nitrogen fixation

Question 18

Nodules (leghemoglobin)

Answer 18

of nodules depend on soil and light, red due to leghemoglobin

Question 19

Protein secretion in bacteria

Answer 19

7 systems:
type 1 and iv gram -/+
types 2, 3, 4 are unique to gram -

Question 20

translocation

Answer 20

movement of proteins from cytoplasm to or across plasma membrane

Question 21

posttranslational
co-transitional (translocation)

Answer 21

-using signal peptides to deliver pre-protein secretion system
-Using signal recognition particle proteins to bind protein as its leaving ribosome to deliver to secretion

Question 22

secretion

Answer 22

movement of proteins from the cytoplasm to external environment

Question 23

General secretion (type 1)

Answer 23

across plasma membrane
sec - unfolded proteins with SP across
Tat - Folded proteins with twin arginine signal sequence
YidC - folding and translocating plasma membrane proteins

Question 24

Sec/Tat-dependent

Answer 24

type 2/5: deliver proteins across OM after sec or tat

Question 25

Sec/tat independant

Answer 25

Type 3: injection of virulence factors to host
Type 4: protein and Dna transport to host
Type 6: bacterium-bacterium translocation