Genome reduction and gene duplication Flashcards
Why would microbes shrink?
- Generalist
- less costly
- minimalistic lifestyle an advantage
- Habitat provides limited substrates and nutrients
- Habitat is stable sp support limited metabolic range
Why would microbes expand?
- Specialist
- costly but flexible lifestyle.
- Habitat provides substrates and nutrients
- Habitat is unpredictable but requiring large flexible metabolic capacity
The relationship between lifestyle and large genome size?
- Free-living organisms
- Host-associated/ Facultative symbionts
- High per cent GC and large Genome size.
The relationship between lifestyle and small genome size?
- Free-living auxotrophs
- Obligate symbionts
- intracellular parasites
- Smaller genomes and low Genome size.
What are auxotrophs?
Organisms inability to produce certain organic compound for its growth.
Types of dependent lifestyles and small cells works (small genome).
- Free-living auxotroph has no host
- Obligate episymbiont living on the host.
- Obligate endosymbiont or intracellular pathogen living inside the host.
Why genome reduction in free-living bacteria/ archaea (auxotrophy)?
- Loss of genes for essential biosynthetic pathways
- depends on other organisms to grow
What is genome stream-lining in free-living bacteria?
The leaky bacterial helpers (larger genomes) and auxotrophic beneficiaries (smaller genomes). The smaller genome will lose gene (mutation) as it relies on a larger genome. Resulting in the mutated small genome will dependent on the large genome.
What is obligate episymbiont?
The host Ignicaccus can grow with N. equitans, but the N. equitans cant without ignicaccus.
What is endosymbiont or intracellular pathogen?
The parasite lives in host with a highly stable environment.
The implication of genome stream-lining: low GC
Guanine and cytosine are energetically more costly. Smaller genome have fewer DNA repairs genes, which mean an increase in common point mutation ( Cytosine -> Uracil -> Thymine).
What are pseudogenes?
non-functional genes.
How does a genome shrink?
- creation of pseudogenes
- gene deletion
How is the creation of pseudogenes?
The initial stage of genome streamlining:
- Genes: unneeded
- The mutation occurs, and are not selected against
- loss of function of unneeded genes.
The final stage of genome streamlining:
- Loss of gene > genes gained
what are the extreme examples of genome streamlining?
Cyanobacteria to chloroplast
Alphaproteobacteria to mitochrondria.
