How To Solve A Problem Like Eukaryagenesis? Flashcards
Early tree of life analysis
Suggested that eukaryotic primary branch was amitochondrial
The Archezoa hypothesis
- stepwise model of eukaryotic evolution
- Eukaryotes sister to archaea
- deep branching amitochondriates were primitively amitochondrial
Deep branching amitochondriates
- Microsporidia
- Trichomonas
- Giardia
- Entamoeba
- minimised/partial EM
- smaller ribosomes
Archaezoal demise
- mitochondrial protein import genes show α-proteobacterial ancestry
- Microsporidia: mitochondria-derived compartment
CPN60
- Trichomonas vaginalis
- Entamoeba histolytica
mtHSP70
- Nosema locustae
- Encephalitozoan cuniculis
Microsporidia
- mtHSP70 localisation
- iron-sulphur cluster biosynthesis
Secondary mitochondrial reduction
- 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
Entamoeba
Acquired iron-sulphur cluster biosynthesis from archaea via alternative cytoplasmic mechanism
All amitochondriates tested are
Secondarily amitochondrial
Phagotrophic origin hypothesis
- EM -> phagotrophy: catalysed eukaryagenesis
1) loss of rigid cell wall
2) flexible surface membrane
3) membrane internalisation
4) EM
5) Phagotrophy
6) endosymbiosis
Phagotrophy
- phagocytosis for the purpose of feeding
- complex EM
- protein targeting to lysosome for phagosome fusion
- gene transfer ratchet
Doolittle’s Hypothesis
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
Hydrogen Hypothesis
- mitochondria early: provides energetic capacity for diversification
- α-proteobacterial endosymbiosis arose from anaerobic/hydrogen syntrophy w/archael cell
- catalyst for eukaryagenesis
HH predictions
2) anaerobic pathway (hydrogenase, PFO) ancestral of α-proteobacterial endosymbiosis
2) α-proteobacteria underwent HGT
3) power available per cell + gene number ^^
Testing HHP1 using phylogenomics
- anaerobic ATP pathway signal is not α-proteobacterial
- hydrogenase signal: chlamydia-like bacteria
Chlamydia
Intracellular parasites (like α-proteobacteria)
Explaining HHP1 observations
1) chlamydia early -> challenges HH (anaerobic pathway not from mitochondrial progenitor)
2) chlamydia late
Is the α-proteobacterial proto-mitochondrion carrying chlamydial genes
Multi-species syntrophy
- 3x interactions
Lake’s Archaea-First Hypothesis
1) archael eocyte engulfed by Gram -ve bacterium, to form nucleated proto-eukaryote
2) mitochondrial endosymbiosis
Inside-Out theory
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
Mitochondria Early-Late?
- 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)
Stepwise eukaryagenesis
1) archaea
2) archaea + actinobacteria
3) ESPs
4) bacteria : α-proteo, δ-proteo, chlamydia
Asgard archaea
- revealed w metagenomics
- close to Eukaryotes
- isolated from Loki’s castle (between Greenland and Norway)
Asgard ESPs
- metagenomic assembly
- cell division
- cytoskeleton
- EM
- organelles
- contamination
- incomplete sampling
Candidatus Prometheoarchaeum syntrophicum MK-D1
- 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
Current hypothesis?
1) Candidatus Prometheoarchaeum syntrophy
2) anaerobiosis-> aerobiosis
3) proto-mitochondria acquisition + intracellular EM
4) phagotrophic ratchet
Syntrophy
- nutritional exchange: “bartering”
- likely driver of prokaryote-prokaryote conglomeration