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BM211: Introduction to Microbiology > Block E Lecture 2: Microbial Symbiosis and Endosymbiosis > Flashcards

Block E Lecture 2: Microbial Symbiosis and Endosymbiosis Flashcards

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1
Q

What is the definition of symbioses?

A

A close and long-term interaction between individuals of different species
(Slide 4)

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2
Q

What is the “Spectrum” of symbioses relationships?

A

It is a cost-benefit spectrum ranging between parasitism (one organism benefits and the expense of the other) and mutualism (both organisms benefit) with commensalism (one organism benefits and the other is neither harmed or benefits from the relationship) being in the middle
(Slide 4)

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3
Q

What can shift a symbiotic relationship along the “spectrum”?

A

Costs / benefits from the relationship changing over time
(Slide 4)

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4
Q

What is the purpose of quorum sensing?

A

To regulate expression of genes involved in virulence / mutualism - i.e to influence their behaviours based on population density
(Slide 6)

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5
Q

What does quorum sensing allow?

A

Co-ordinated gene expression by bacterial cells
(Slide 6)

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6
Q

What occurs in quorum sensing?

A

A small diffusible autoinducer molecule interacts with a receptor at a certain threshold concentration - resulting in changes in gene expression
(Slide 6)

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7
Q

Why is quorum sensing not inter-species?

A

As the autoinducer is species-specific
(Slide 6)

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8
Q

What do Pattern-Recognition Receptors (PRRs) recognise?

A

Microbe-Associated Molecular Patterns (MAMPs) - aka Pathogen-Associated Molecular Patterns (PAMPs)
(Slide 7)

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9
Q

Why can Pattern recognition receptors (PRRs) cause problems when it comes to beneficial microbes in the body?

A

As they also exhibit PAMPs, and the body must tolerate them despite this fact
(Slide 7)

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10
Q

In some cases why may happen to PAMPs that beneficial microbes inside the body have?

A

They may be able to mask, change or lose the PAMP to evade triggering PRRs
(Slide 7)

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11
Q

What are 3 examples of symbioses?

A

Euprymna scolopes and Aliivibrio fischeri
Legumes and rhizobia
Endosymbiotic theory
(Slide 8)

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12
Q

What does Aliivibrio fischeri exhibit in dark conditions?

A

Bioluminescence
(Slide 9)

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13
Q

What kind of bacteria is Aliivibrio fischeri (gram positive / negative + class)?

A

It is a gram-negative bacteria in the gammaproteobacteria class
(Slide 10)

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14
Q

What does the Aliivibrio fischeri genome consist of?

A

2 circular chromosomes
(Slide 10)

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15
Q

What animal is Euprymna Scolopes?

A

It is a squid (Hawaiian bobtail squid to be specific)
(Slide 10)

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16
Q

What happens when the Euprymna scolopes squid is immature concerning the A. fischeri symbiotic relationship?

A

The immature squid is colonised by free-living A. Fischeri present in the environment
(Slide 11)

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17
Q

What part of the immature Euprymna scolopes squid does A. fischeri colonise?

A

A specialised light organ
(Slide 11)

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18
Q

What happens after A. fischeri colonise Euprymna scolopes specialised light organ?

A

The establish an infection and divide using host supplied nutrients, with the squid being able to control the amount of bacteria in the light organ
(Slide 11)

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19
Q

How does Euprymna Scolopes ensure only A. fischeri colonises it?

A

Host mucus contains a chemoattractant (chitobiose) and immunity factors that may inhibit other bacteria
(Slide 12)

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20
Q

What do recruited A. fischeri cells bind to and what do they induce?

A

They bind to host cilla and induce changes in gene expression
(Slide 12)

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21
Q

Where do A. fischeri cells move into after they bind to the squid’s cilla?

A

They move into pores and then into the crypts within the specialised light organ(at an average of 1/cell a crypt)
(Slide 12)

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22
Q

Approximately how long does it take A. fischeri to produce bioluminescence after moving into the light organ?

A

12 hours
(Slide 12)

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23
Q

What does Aliivibrio fischeri colonisation of the light organ lead to?

A

Light organ morphogenesis
(Slide 13)

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24
Q

What do Aliivibrio fischeri MAMPs signal for after they colonise Euprymna scolopes?

A

They signal for cell death and destruction of the ciliated surface originally used for the colonisation
(Slide 13)

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25
Q

What cells are A. fischeri cells in direct contact with after they enter the crypt spaces?

A

Epithelial cells
(Slide 13)

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26
Q

What 2 host behaviours change in the Euprymna scolopes squid after it becomes mature?

A

Host switches from being arrhythmic to being completely nocturnal and a diel/circadian (24 hour cycle) pattern of host and symbiont behaviour is established
(Slide 14)

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27
Q

What 3 things happen in the diel/circadian (24 hour cycle) pattern in the Aliivibrio-squid symbioses?

A

Transcriptomes oscillates
Restructuring of the host crypt epithelium
Bacterial metabolism changes
(Slide 14)

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28
Q

What bacterial metabolism changes occur in the day/night cycle of the Aliivibrio-squid symbiosis?

A

During the day the Aliivibrio fischeri likely use host membranes for regrowth whereas at night time they may switch to chitin fermentation, a substance probably provided by the host
(Slide 14)

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29
Q

Roughly what percentage of Aliivibrio fischeri bacteria does the squid expel at dawn?

A

~90%
(Slide 14)

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30
Q

What does the squid releasing Aliivibrio fischeri into the environment result in?

A

The environment being seeded with Aliivibrio fischeri which can colonise new hosts
(Slide 14)

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31
Q

What is one possible theory on why the squid releases Aliivibrio fischeri into the environment?

A

May be to sanction dark or underperforming mutants
(Slide 14)

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32
Q

Why do bacteria only turn on their bioluminescence when its needed?

A

As it is energetically expense
(Slide 15)

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33
Q

How does the autoinducer produce a specific Acyl-homoserine lactose?

A

The autoinducer synthesises Luxl which produces a specific Acyl-homoserine lactose (AHL)
(Slide 16)

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34
Q

How does the regulator LuxR help direct transcription of target gene?

A

It binds to the Acyl-homoserine lactose (AHL) when the AHL is at a high concentration and directs transcription of target genes
(Slide 16)

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35
Q

What quorum sensing system do Aliivibrio fischeri bacteria use?

A

A two quorum system
(Slide 17)

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36
Q

What is the first step of a two quorum sensing system?

A

AinS produces C8, which is sensed by AinR
(Slide 17)

37
Q

What happens after AinR senses C8 in a two quorum sensing system?

A

It leads to deprepression of LitR which leads to LuxR expression
(Slide 17)

38
Q

What happens after LuxR is expressed in a 2 quorum sensing system?

A

Luxl produces 3OC6 which is then sensed by LuxR
(Slide 17)

39
Q

What happens after 3OC6 is sensed by LuxR in a 2 quorum sensing system?

A

LuxR binds the lux box and activates expression of structural genes required for bioluminescence
(Slide 17)

40
Q

What is an example of a gene which is required for bioluminescence in Aliivibrio fischeri and what does it do?

A

LuxAb luciferase
(Slide 17)

41
Q

What must nitrogen (N2) be “fixed” into for it to become biologically accessible?

A

Ammonia (NH3)
(Slide 19)

42
Q

What process is used to produce ammonia from nitrogen?

A

The Haber process
(Slide 19)

43
Q

What type of bacteria (gram positive/negative) are Rhizobial bacteria and what 2 classes are they a part of?

A

They are gram-negative members of the alpha and betaproteobacteria classes
(Slide 20)

44
Q

Where are rhizobial bacteria found?

A

They are free-living in soil or in association with legumes (root nodules)
(Slide 20)

45
Q

What does each rhizobial bacteria species having many different biovars of each species, depending on the host plant mean?

A

Biovar is short for “biological varieties” with the phrase meaning that there are many different strains within a species which are adapted to different host plants
(Slide 20)

46
Q

What are the 6 steps in the rhizobium-legume symbioses?

A
  1. Flavonoids
  2. Nod factor
  3. Formation of the root nodules
  4. Nodule development and bacteroid differentiation
  5. Nodule function
  6. Nodule senescence
    first 3 steps are formation steps
    (Slide 21)
47
Q

What is the rhizosphere?

A

The region of soil around plant roots, which is affected by plant exudates (substances released or excreted by plant roots into the soil)
(Slide 22)

48
Q

What is the first step in the flavonoid signalling step of the rhizobium-legume symbiosis?

A

Plant roots release flavonoids when nitrogen is scarce
(Slide 23)

49
Q

What do flavonoids released by plant roots do?

A

They can diffuse across rhizobial membranes and act as signals
(Slide 23)

50
Q

What are 2 things which make rhizobium-legume symbiosis specific?

A

Different plants produce different profiles of flavonoids and there is also variation amongst rhizobia in their ability to sense and respond to particular flavonoids
(Slide 23)

51
Q

What is the first step in the Nod factor step of the rhizobium-legume symbiosis?

A

Plant flavonoids in the bacterial cytoplasm bind to the transcription factor NodD
(Slide 24)

52
Q

What occurs in the rhizobium-legume symbiosis after the plant flavonoids bind to the NodD transcription factor?

A

NodD activates expression of the nod genes
(Slide 24)

53
Q

What do the nod gene products do after NoD activates their expression in the rhizobium-legume symbiosis?

A

Nod gene products synthesise nod factors
(Slide 24)

54
Q

What are Nod factors perceived by?

A

LysM-RLKs
(Slide 25)

55
Q

What are 3 changes which happen when Nod factors are perceived by LysM-RLKs?

A

Calcium concentrations spike
Root hair deformation
Formation of the infection thread
Nodule organogenesis
(Slide 25)

56
Q

What is the first step which occurs in root nodule formation (in the rhizobium-legume symbiosis)?

A

The rhizobium bacteria recognise the plant which released the flavonoid signal and attach to the plant root
(Slide 26)

57
Q

What happens in root nodule formation after the rhizobium bacteria attach to the plant’s roots?

A

The bacteria secrete nod factors causing root hair curling and infection thread formation
(Slide 26)

58
Q

What occurs in root nodule formation after the release of nod factors by the rhizobium bacteria?

A

The rhizobium bacteria penetrate the root hair and multiple within an infection thread
(Slide 26)

59
Q

What happens in root nodule formation after the rhizobium bacteria begin to multiply within an infection thread?

A

The infection thread begins to grow towards the root cell
(Slide 26)

60
Q

What occurs in root nodule formation after the infection thread starts to grow towards the root cell?

A

Formation of bacteroid state within plant root cells
(Slide 26)

61
Q

What does the bacteroid state refer to?

A

The differentiation of rhizobium bacteria into their specialised form in order for them to adapt to life within the plant root cell
(Slide 26)

62
Q

What occurs after the bacteroid state forms within plant root cells and is the final step of root nodule formation?

A

Continued plant and bacterial cell division leads to nodule formation
(Slide 26)

63
Q

Does the bacteria or the plant control the process of rhizobium bacteria differentiating into bacteroids?

A

It is controlled by the plant
(Slide 28)

64
Q

How does the plant control the process of the rhizobium bacteria differentiating into bacteroids?

A

The plant releasing signals such as nodule-specific cysteine-rich peptides (NCRs)
(Slide 28)

65
Q

What are 3 changes bacteroids have when compared to free-living cells?

A

Answers Include:
Cell morphology
DNA content
Gene expression
Metabolism
(Slide 28)

66
Q

What genes do rhizobium bacteria express after they differentiate into bacteroids, and what do these do?

A

Nif genes, which produce the enzyme nitrogenase, which catalyses the fixation of nitrogen (N2) into ammonia (NH3)
(Slide 28)

67
Q

What may the plant be able to do to non-N2 fixing rhizobium bacteroids?

A

“Sanction” them
(Slide 28)

68
Q

Rhiobium bacteria provide the plant with fixed nitrogen in the form on ammonia. What does the plant give back in this relationship?

A

They give the bacteroids a C source (in the form of dicarboxylates)
(Slide 29)

69
Q

What is the purpose of the nodules which rhizobium bacteria form?

A

As the plant can use it to create a specialised nitrogen fixing environment which is microoxic (contains very small concentrations of oxygen) environment
(Slide 29)

70
Q

Why does a microoxic (contains very small concentrations of oxygen) environment create a specialised environment for nitrogen fixation?

A

As nitrogenase is extremely sensitive to O2
(Slide 29)

71
Q

What do nodules eventually do?

A

They eventually senesce, though this is poorly understood
(Slide 29)

72
Q

What does senesce mean?

A

Deteriorate with age
(Slide 29)

73
Q

What is primary endosymbiosis?

A

Primary endosymbiosis refers to the process by which a eukaryotic cell engulfs a prokaryotic cell and establishes a symbiotic relationship that eventually leads to the integration of the prokaryotic cell
(Slide 31)

74
Q

What is secondary endosymbiosis?

A

When a eukaryotic cell engulfs another eukaryotic cell which has already undergone primary endosymbiosis, which the engulfed eukaryotic cell becomes a symbiont of the host cell
(Slide 31)

75
Q

What is the endosymbiont theory?

A

That chloroplasts and mitochondria have been suggested to be descendants of ancient prokaryotic cells (Cyanobacteria for chloroplasts and Rickettsiales for mitochondria)
(Slide 31)

76
Q

What are 3 pieces of evidence which support the endosymbiont theory?

A

Answers Include:
1. Mitochondria and chloroplasts have their own chromosomal DNA
2. Mitochondria and chloroplasts have their own ribosomes (70S)
3. Antibiotics that affect prokaryotic ribosome function work against mitochondria and chloroplasts
4. Eukaryotic genes often contain genes derived from bacteria
5. DNA sequencing reveals that mitochondria and chloroplast DNA is phylogenetically related to bacteria
(Slide 32)

77
Q

How are mitochondria semi-autonomous?

A

They can make some of their own proteins using their own ribosomes and their own DNA, but many proteins and functions are supplied by the host
(Slide 33)

78
Q

How do mitochondria grow?

A

They grow and divide like bacteria (growth -> fission -> segregation)
(Slide 33)

79
Q

What form are mitochondrial and chloroplast genomes in?

A

dsDNA and are usually circular
(Slide 34)

80
Q

What process have mitochondrial and chloroplast genomes underwent as they have become integrated into their respective hosts?

A

Extreme genome reduction - having just dozen of genes left
(Slide 34)

81
Q

What has happened to many genomes/ functions that mitochondria and chloroplasts have lost?

A

They have been transferred to the nucleus
(Slide 34)

82
Q

What are the 5 steps in the Co-evolutionary timeline in which an organism is converted from being free-living and extracellular into being an organelle?

A
  1. Free-living and extracellular
  2. Facultative intracellular (early stage)
  3. Obligate intracellular (advanced stage)
  4. Obligate intracellular mutualist]5. 5. Organelle
    (Slide 35)
83
Q

What occurs in each stage of the co-evolutionary timeline which shows an organism being converted from being free-living and extracellular to being an organelle?

A

It’s genome is reduced
(Slide 35)

84
Q

Why do insects often have primary symbionts?

A

As they are often required for reproduction
(Slide 36)

85
Q

In addition to having primary symbionts, what may insects also have?

A

Secondary symbionts
(Slide 36)

86
Q

What occurs in the aphid and buchnera aphidicola symbiotic relationship?

A

The buchnera synthesise amino acids for the aphid insects as their diet contains low amounts of these essential amino acids
(Slide 36)

87
Q

What is an example of symbiosis in humans?

A

Complex microbiomes such as the skin and gut microbiomes
(Slide 37)

88
Q

What does microbial symbiosis contribute to in humans?

A

Immune development, metabolism and many other functions
(Slide 37)

89
Q

Are our microbiomes dynamic or static?

A

Dynamic - as they change over time depending on various conditions
(Slide 37)

BM211: Introduction to Microbiology (21 decks)

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