lect 17 - prokaryotic evolution Flashcards
(30 cards)
examples of prokaryotes
bacteria and archaea
what does genomics or genome sequencing allow for ?
not relying only on prokaryotes grown in labs
allowed for the discovery, characterization, and studying diversity of many things
jean-marie volland discovery
biggest single cell bacteria every found
mangroves in guadelope
biggest single cell bacterium found
jean-marie volland
lives by oxidizing sulphur
genetic info stored in hundreds of thousands of pepins - compartmentalized structures not seen before
pepins
compartmentalized structures found in biggest found bacterium
genetic info stored here
holding extra copies of genome
longest bacterium name
thiomargarita magnifica
3 key features of prokaryotic evolution
most proks are good at acquiring and/or exchanging DNA via horizontal transfer
prok cells are typically haploid - so no dom or recessive - everything is expressed
most proks have very big population sizes — so genetic drift not as important
how does genetic drift effect prokaryotic evolution?
since prokaryotes often have very large population sizes, genetic drift is not as strong as smaller pops
features of bacterial genomes (3 points)
small bacterial genome sizes are associated with bacteria that cannot live freely (live in host)
larger bacterial genome sizes are associated with free-living (no host)
very little non-coding DNA (unlike euks)
genome size of bacteria vs euks
very little non-coding DNA, intergenic DNA, and pseudogenes in bacterial genomes
lots of non-coding etc (junk) in euks
3 major modes of DNA exchange prokaryotes
conjugation (plasmid-mediated)
transduction (virus=phage or transposable element-mediated)
transformation (uptake from environment)
homologous recombination prokaryotes
in prokaryotes. this is similar to gene flow and sexual recombination in euks
non-homologous recombination prokaryotes
prokaryotes are good at bringing in new genetic material
new material through lateral gene transfer or horizontal gene transfer
why is horizontal gene transfer beneficial and who does it ?
brings in new genetic material for prokaryotes (sometimes in euks but small scale)
major source of innovation and adaptation in proks
how do you detect horizontal gene transfer? (3 points)
phylogenetic analysis
sequence features (like percent GC content)
interesting neighbours imply horizontal gene transfer (like being next to virus genes)
what kind of genes are transferred through horizontal gene transfer?
almost ANYTHING is documented to be horizontally transferred
for example:
- virulence genes
- antibiotic resistance genes (plasmid mediated)
- etc
example of lateral gene transfer
the sushi gene
transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota
Jan-Hendrick Hehemann
the sushi gene
example of lateral gene transfer
novel enzymes found in marine bacteria that break down seaweed called porphyranases — high specificity to break down
marine bacteria hangs out and grows on seaweed
good at breaking down certain seaweed structures
porphyranase enzymes
found in marine bacteria and part of the gut microbiome of Japanese ppl (Bacteroides plebeius or Bp)
acquired these enzymes by lateral gene transfer from marine bacteria — from being exposed to a lot of seaweed
prokaryotic genomes are often very _____
dynamic
they are constantly gaining and losing genes
closely related strains often hv differences in gene content
- shared core genes
- non-core (accessory) genes that are often ecologically important
2 examples of closely related strains that have differences in gene content
Bacteroides plebeius (Bp) - japanese gut enzyme
Prochloroccus
- marine cyanobacterium
- one named species but lots of variation — genomic islands
Prochlorococcus
marine cyanobacterium responsible for abt 20% of earths oxygen production
1 named species with lots of variation
genomic islands — lots of shared genes, but whole part of genome has completely different gene content
often associated w phage sequences
found in genomic islands — sequenced from phage —> shows horizontal gene transfer
genomic islands example and what might each different strain tell us (3 things) ?
Prochloroccus
2 strains of the one named species
when strain specific, might tell us about local specific conditions in relation to:
- nutrient acquisition
- adaptation to environmental conditions
- defence against viruses and predators
DYNAMIC — good at getting things out and bringing stuff in
what does it mean that prokaryotic genomes are dynamic ?
they are constantly bringing stuff in and getting stuff out
bringing stuff in via lateral (horizontal) gene transfer
genomes are still small with little non-coding DNA or pseudogenes
