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Michaelmas Term 1 > The social microbe II – interactions of microbes and macrobes > Flashcards

The social microbe II – interactions of microbes and macrobes Flashcards

1
Q

List some microbial interactions

A
  • hosts
  • mutualists
  • commensals
  • symbionts
  • pathogens
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2
Q

Describe commensal

A
  • an animal or plant which lives attached to or as a tenant of another, and shares its food
  • distinguished from a parasite, which feeds on the body of its host
  • also applied to the host itself
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3
Q

Describe symbiosis

A

association of two different organisms which live attached to each other, or one as a tenant of the other, and contribute to each other’s support.

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4
Q

Define infection

A

colonisation of the host from an infection source

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5
Q

Define transmissibility

A

ability to spread from host to host

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6
Q

Define carriage

A

establishment of a long-term harmless relationship

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7
Q

Define disease

A

infections that damage the host (pathology)

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8
Q

Define pathogenicity

A

ability to cause disease

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9
Q

Define virulence

A

severity of disease caused

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10
Q

Describe soil amoeba

A
  • exhibit all types of interactions with bacteria
  • prey on bacteria as a food source
  • bacteria can parasitise them,
  • pre-adapted to parasitise phagocytes
  • have endosymbiotic mutualists
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11
Q

List some intracellular lifestyle

A
  • predator-prey
  • parasitism
  • mutualism
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12
Q

What are the implications of the intracellular predator-prey lifestyle?

A
  • food web and nutrient cycling
  • selective force for bacterial community
  • mechanisms of intracellular killing
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13
Q

What are the implications of the intracellular parasitic lifestyle?

A
  • discovery of new pathogens
  • identification of new virulence factors
  • drinking water safety
  • human health
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14
Q

What are the implications of the intracellular mutualistic lifestyle?

A
  • mechanisms of genome reduction and gene transfers
  • coadaptation in endosymbiosis
  • origin of organelles
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15
Q

Explain diverging host associations

A
  • very large ancient population of free living bacteria undergoes recombinational change
  • infection causes host association
  • diverges into mutualism and pathogenesis
  • forms commensal and pathogen respectively
  • forms symbiont and obligate respectively
  • forms smaller, younger populations
  • limits recombinational exchange
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16
Q

Describe the stages of host adaptation

A
  • free living and extracellular microbe acquires genes by HGT, causes changes within the genome
  • forms early stage facultative intracellular microbes; gene loss
  • forms advanced stage obligate intracellular microbe
  • forms extreme stage obligate intracellular mutualist
  • forms organelle
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17
Q

What are the roles of the mycobiont in lichens

A
  • protection of the photobiont
  • absorb mineral nutrients.
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18
Q

What are the roles of the prokaryotic photobiont in lichens

A
  • synthesis of organic nutrients
  • nitrogen fixation
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19
Q

Describe Rhizobium and Fabaceae

A
  • major source of fixed nitrogen for plants
  • species-specific for bacteria and plants
    – co-evolution of host and symbiont
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20
Q

Describe the role of the plant in the legume/rhizobium symbiosis

A
  • nutrition
  • low oxygen tension (leghaemoglobin)
  • protection
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21
Q

Describe the role of the bacterium in the legume/rhizobium association

A

nitrogen fixation

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22
Q

Describe the formation of Rhizobium root nodules

A
  • recognition and attachment
  • invasion
  • travel through infection thread
  • bacteroid formation
  • bacterial and plant growth to form the nodules
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23
Q

Describe the Verminephrobacter symbiosis in earthworms

A
  • almost all earth worms harbour species-specific
    endosymbionts
  • Verminephrobacter
  • vertically transmitted
  • evolutionary ancient association.
  • bacteria live on host waste products.
  • beneficial for host reproduction (nutritional advantage)
  • reductive evolution of the bacterial genome results in streamlining
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24
Q

Describe the nephridia of an earthworm

A
  • clitellum
  • intestine
  • septum
  • pore to exterior
  • nephrostome (intake)
  • 1st loop
  • 2nd loop
  • ampulla
  • 3rd loop bladder
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25
Q

Describe the genome evolution of vertically transmitted extracellular symbionts

A
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26
Q

Describe Verminephrobacter symbionts

A
  • high host fidelity
  • vertical transmission
  • extracellular lifestyle
  • scope for HGT
  • different pattern of genome evolution from intracellular symbionts
  • two different environments: nephridia and cocoon
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27
Q

Describe free-living microbes

A
  • recombination within and between populations
  • few pseudogenes
  • few mobile elements
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28
Q

Describe the genetics of Verminephrobacter

A
  • genetic mixing, fluctuating environment
  • ongoing uptake and loss of genes
  • many mobile elements and genome rearrangements
  • accelerated evolutionary rates
  • few pseudogenes
  • no genome reduction
  • continuous genome rearrangements
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29
Q

Describe the genetics of insect endosymbioses

A
  • no genetic mixing, stable environment
  • host restriction
  • accumulation of pseudogenes
  • expansion of mobile elements
  • chromosomal rearrangements
  • accelerated evolutionary rates and gene loss
  • loss of mobile elements
  • few pseudogenes
  • small and stable genome; AT-bias
30
Q

Describe aphid symbionts

A
  • Buchnera genus
  • e.g. Acyrthosiphon pisum (pea aphid)
  • e.g. Schizaphis graminum (wheat aphid)
31
Q

List some ant symbionts

A
  • Blochmannia floridanus
  • Blochmannia pennsylvanicus
32
Q

List a Tsetse fly symbiont

A

Wigglesworthia glossinidia brevipalpis

33
Q

Describe bligate mutualistic insect endosymbionts

A
  • P-symbionts
  • restricted to bacteriome
  • domesticated by the host
  • cannot invade naïve hosts
  • dependent on host-based mechanisms for transmission
34
Q

P-symbionts

A

primary symbionts

35
Q

bacteriome

A

consists of specialised host cells (bacteriocytes)

36
Q

Describe facultative insect endosymbionts

A
  • S-symbionts
  • erratically distributed
  • not required for host reproduction
  • resemble pathogens
  • can colonize uninfected hosts & establish stable, maternally inherited infection
  • can confer benefits, including protection against natural enemies
37
Q

S-symbionts

A

secondary symbionts

38
Q

Describe facultative insect endosymbiont pathogen resemblance

A

invade cells, including reproductive organs

39
Q

Describe insect endosymbiotic reproductive manipulators

A
  • parasites that spread by increasing host reproduction through females offspring;
  • through reproductive incompatibility between infected and uninfected insects
  • infected males sterilise uninfected females
  • e.g. Wolbachia spp.
40
Q

Describe Buchnera

A
  • obligate intracellular
    endosymbionts of aphids.
  • without the bacteria the aphids die of starvation
  • bacteria are maternally transmitted
    – and therefore co-evolve with the aphid
41
Q

Describe Buchnera phylogeny

A
  • most Buchnera genes have close homologues in the Enteric bacteria
  • the distant ancestor of Buchnera was probably somewhat like present day Escherichia coli, that has undergone extensive reductive evolution
42
Q

Describe the metabolic interdependence of Aphids and Buchnera

A
  • bacteria located in
    ‘bacteriocytes’
  • surrounded by an aphid-derived membrane;
  • unculturable
  • vertically transmitted via the ovary
43
Q

bacteriocytes

A
  • specialised insect cells
  • aka mycetocytes
44
Q

Describe the host role in the Aphid-Buchnera symbiosis

A

supplies energy, carbon, and nitrogen, in the form of glutamine from phloem

45
Q

Describe the symbiont role in the Aphid-Buchnera symbiosis

A

production of amino acids, especially tryptophan (12
to 16 copies of trpEG genes).

46
Q

Describe the long-term co-evolution of Aphid-Buchnera

A
  • mutualistic symbiosis
  • probably established 150 to 250Mya
47
Q

Describe Wolbachia

A
  • large group of intracellular alphaproteobacteria
    endosymbionts
  • restricted to Ecdysozoan species
  • essential for survival and reproduction of nematodes: mutualists
  • present in ~66% of insects
  • infect the germ line
  • often manipulate host sex ratios for their own benefit: pathogenic capacity
48
Q

Who is Wolbachia related to?

A
  • Anaplasma
  • Ehrlichia
  • Rickettsia
49
Q

Who does Wolbachia infect?

A
  • terrestrial arthropods
  • filarial nematodes
50
Q

Describe the four reproductive phenotypes of Wolbachia

A
  • feminisation of genetic males
  • parthenogenic elimination of males from reproduction
  • male killing of infected males
  • cytoplasmic incompatibility
51
Q

Whose genetic males do Wolbachia feminise?

A
  • Hemiptera
  • Isopoda
  • Lepidoptera
52
Q

For which groups does Wolbachia do parthenogenic elimination of males from reproduction?

A
  • Acari
  • Hymenoptera
  • Thysanoptera
53
Q

For which groups does Wolbachia do male killing of infected males?

A
  • Coleoptera
  • Diptera
  • Lepidoptera
  • Pseudoscorpiones
54
Q

Describe cytoplasmic incompatibility in Wolbachia

A

prevents infected males mating with females without the
same Wolbachia

55
Q

For which groups does Wolbachia do cytoplasmic incompatibility?

A
  • Acari
  • Coleoptera
  • Diptera
  • Hemiptera
  • Hymenoptera
  • Isopoda
  • Lepidoptera
  • Orthoptera
56
Q

Describe the use of Wolbachia for disease vector control

A
  • release of Wolbachia-infected males into wild populations where Wolbachia is absent
  • release of females harbouring Wolbachia
  • release of Wolbachia wMelPop via females
57
Q

Describe the release of Wolbachia-infected males into wild populations where Wolbachia is absent

A

reproductive incompatibility with wild females results
in embryonic death of offspring.

58
Q

Describe the release of females harbouring Wolbachia

A
  • offspring with Wolbachia have reduced competence as pathogens vectors
  • as only females transmit disease, males not used
  • Wolbachia spreads via cytoplasmic incompatibility
59
Q

Describe the release of Wolbachia wMelPop via females

A
  • pathogen blocking and spread via cytoplasmic incompatibility
  • reduces insect lifespan, further decreasing pathogen transmission
60
Q

Describe termite symbioses

A
  • symbiotic associations with hindgut microbiota are essential to utilise complex biopolymers
  • flagellates and bacteria occur in the gut of lower termites
  • higher termites possess only bacteria
  • e.g. spirochetes
61
Q

complex biopolymer

A

wood

62
Q

Describe cellulose and symbioses

A
  • metabolic pathways to utilise cellulose has evolved in many bacterial groups
  • form the bases of many symbioses
63
Q

Describe carbohydrate polymers

A
  • abundant biological molecules
  • used for storage or as structural components
64
Q

Describe cellulose

A
  • linear polymer of glucose
  • most common carbohydrate synthesised by plants
  • key part in the carbon cycle.
  • insoluble crystalline microfibrils: highly resistant to enzymic hydrolysis.
65
Q

Describe ruminants

A
  • digest cellulose for 9-12 hours
  • variety of bacteria convert polymers such as cellulose to glucose and then to fatty acids
66
Q

Describe the rumen

A

large (100-150l) fermenter kept at constant temperature

67
Q

Describe the Hawaiian bobtail squid (Euprymna scolopes)- Vibrio fischeri Symbiosis

A
  • light generated by Vibrio fischeri bacterial symbionts camouflage Hawaiian bobtail squid
  • prey animals cannot see the squid’s shadow from below.
  • squid mucus attracts many bacterial species of into the light
    organ
    – ciliated cells create a current that expels most bacteria, and hydrogen peroxide creates an environment that only Vibrio fischeri survive
  • inside the light organ, Vibrio fischeri is provided with sugars and amino acids
  • daily rhythm of alternating symbiont metabolism between glycerol phosphate respiration and chitin fermentation facilitates luminescence
  • light organ becomes acidic at night, increasing oxygen availability
  • female squid have a second symbiotic organ containing a simple symbiotic community
68
Q

Describe the holobiont

A

organisms are an expression of a combination of their genome and their microbiota.

69
Q

Describe the human microbiota

A
  • dynamic
  • major role in health and disease: dysbiosis
70
Q

Describe the functions of the indigenous microbiota

A
  • catabolism and bioconversion of dietary or host derived compounds can make nutrients more available to the host.
  • synthesise important cofactors or bioactive signaling molecules (e.g. amines)
  • signaling between the microbiota and the host can trigger alterations in host function (e.g. altered expression of mucus or alteration of the immune response)

Michaelmas Term 1 (42 decks)

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