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B3.0 > How To Solve A Problem Like Eukaryagenesis? > Flashcards

How To Solve A Problem Like Eukaryagenesis? Flashcards

1
Q

Early tree of life analysis

A

Suggested that eukaryotic primary branch was amitochondrial

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2
Q

The Archezoa hypothesis

A
  • stepwise model of eukaryotic evolution
  • Eukaryotes sister to archaea
  • deep branching amitochondriates were primitively amitochondrial
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3
Q

Deep branching amitochondriates

A
  • Microsporidia
  • Trichomonas
  • Giardia
  • Entamoeba
  • minimised/partial EM
  • smaller ribosomes
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4
Q

Archaezoal demise

A
  • mitochondrial protein import genes show α-proteobacterial ancestry
  • Microsporidia: mitochondria-derived compartment
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5
Q

CPN60

A
  • Trichomonas vaginalis
  • Entamoeba histolytica
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6
Q

mtHSP70

A
  • Nosema locustae
  • Encephalitozoan cuniculis
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7
Q

Microsporidia

A
  • mtHSP70 localisation
  • iron-sulphur cluster biosynthesis
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8
Q

Secondary mitochondrial reduction

A
  • gets rid of ETC, keep iron-sulphur cluster biosynthesis
  • conserved characteristics
  • mitosomes (Microsporidia)
  • hydrogenosomes (hydrogen generation)
  • nearly every lineage has retained some form of mitochondrial relic (not Entaemoba; branching pattern not ancestral)
  • large scale loss of organelle system and proteome is tolerated
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9
Q

Entamoeba

A

Acquired iron-sulphur cluster biosynthesis from archaea via alternative cytoplasmic mechanism

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10
Q

All amitochondriates tested are

A

Secondarily amitochondrial

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11
Q

Phagotrophic origin hypothesis

A
  • EM -> phagotrophy: catalysed eukaryagenesis
    1) loss of rigid cell wall
    2) flexible surface membrane
    3) membrane internalisation
    4) EM
    5) Phagotrophy
    6) endosymbiosis
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12
Q

Phagotrophy

A
  • phagocytosis for the purpose of feeding
  • complex EM
  • protein targeting to lysosome for phagosome fusion
  • gene transfer ratchet
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13
Q

Doolittle’s Hypothesis

A

1) bacterium digestion by phagotrophy
2) genome incorporation
3) loss ; resident archael copy; new bacterial copy
4) fixation/ loss by drift
5) successful / failed replacement
- potential explanation for prokaryotic origins of cytoplasmic metabolic proteome

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14
Q

Hydrogen Hypothesis

A
  • mitochondria early: provides energetic capacity for diversification
  • α-proteobacterial endosymbiosis arose from anaerobic/hydrogen syntrophy w/archael cell
  • catalyst for eukaryagenesis
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15
Q

HH predictions

A

2) anaerobic pathway (hydrogenase, PFO) ancestral of α-proteobacterial endosymbiosis
2) α-proteobacteria underwent HGT
3) power available per cell + gene number ^^

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16
Q

Testing HHP1 using phylogenomics

A
  • anaerobic ATP pathway signal is not α-proteobacterial
  • hydrogenase signal: chlamydia-like bacteria
17
Q

Chlamydia

A

Intracellular parasites (like α-proteobacteria)

18
Q

Explaining HHP1 observations

A

1) chlamydia early -> challenges HH (anaerobic pathway not from mitochondrial progenitor)
2) chlamydia late
Is the α-proteobacterial proto-mitochondrion carrying chlamydial genes

19
Q

Multi-species syntrophy

A
  • 3x interactions
20
Q

Lake’s Archaea-First Hypothesis

A

1) archael eocyte engulfed by Gram -ve bacterium, to form nucleated proto-eukaryote
2) mitochondrial endosymbiosis

21
Q

Inside-Out theory

A

1) archael eocyte interacts with α-proteobactetia
2) recruits protein to form protrusions; increasing SA of interaction
3) bleb
4) proto-NPs stabilise bleb
5) α-proteobacterium engulfed by nascent mitochondrion
6) blebs fuse; cytoplasm and EM

22
Q

Mitochondria Early-Late?

A
  • measure phylogenetic relative branch lengths of genes encoding different cell components
  • 4 distinct waves of gene acquisition; stepwise eukaryagenesis
  • mitochondria Last
  • heterogenous rates of sequence variation (esp if specific to cell system)
23
Q

Stepwise eukaryagenesis

A

1) archaea
2) archaea + actinobacteria
3) ESPs
4) bacteria : α-proteo, δ-proteo, chlamydia

24
Q

Asgard archaea

A
  • revealed w metagenomics
  • close to Eukaryotes
  • isolated from Loki’s castle (between Greenland and Norway)
25
Q

Asgard ESPs

A
  • metagenomic assembly
  • cell division
  • cytoskeleton
  • EM
  • organelles
  • contamination
  • incomplete sampling
26
Q

Candidatus Prometheoarchaeum syntrophicum MK-D1

A
  • isolated and cultured from deep marine sediment
  • 550nm anaerobic coccus
  • extremely slow-growing
  • syntrophic
  • produces hydrogen (auto-hydrogenase) and formate for interspecies ET ; contradicts HH
  • 80 ESPs
  • no organelles
  • 50-280nm membrane vesicles
  • unique, long, branching protrusions
  • complex
27
Q

Current hypothesis?

A

1) Candidatus Prometheoarchaeum syntrophy
2) anaerobiosis-> aerobiosis
3) proto-mitochondria acquisition + intracellular EM
4) phagotrophic ratchet

28
Q

Syntrophy

A
  • nutritional exchange: “bartering”
  • likely driver of prokaryote-prokaryote conglomeration

B3.0 (26 decks)

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