Lecture 6: Evolution of Microbial Diversity Flashcards
What is the root?
The last universal common ancestor (LUCA)
What does LUCA stand for and what does it mean?
1) Last universal common ancestor
2) Last common ancestry of the 3 domains (bacteria, archaea, and eukarya)
How do we know that Eukarya and Archaea had common ancestry at some point?
Eukarya and Archaea share key proteins
What 3 things should be considered when looking into microbial genetic diversity?
1) The world environment(s)
2) The extraterrestrial
3) Microbial mechanisms (mutations and gene transfer)
Name 2 microbial mechanisms
1) Mutations
2) Gene transfer
What is another word for anagenesis? What does it mean?
1) Genetic drift
2) Defined as small, random genetic changes that occur over generations
What 3 things contribute to anagenesis?
1) Extremely fast microbial growth
2) Type of mutation
3) Selection pressure (adaptive mutation)
-ex: pH, oxygen, temp, etc
Give 3 examples of selective pressures
pH, oxygen, temp
Name 4 mechanisms of genetic variation
1) Gene mutation
2) Gene duplication
3) Gene loss
4) Recombination
Name 2 models for evolutionary mechanisms of diversity and briefly describe them
1)Metapopulation model: Small changes (gradual)
2) Stable ecotype model: Rapid bursts of speciation
1) Describe the metapopulation model of evolutionary mechanisms of diversity
2) What are the 3 ways niches of microbes can expand?
1) There are small changes in the environment along with small changes in the DNA of the organisms.
2) Patches (niches) of microbes can either expand:
a) Clonally
b) Heterogeneously
c) Migrate when nutrients wane
4) All local populations have a chance of extinction
Describe the stable ecotype model of evolutionary mechanisms of genetic diversity
1) Members of microbial population undergo genetic changes
2) So they outcompete the rest, which means that the winners advance and losers go extinct.
3) Results in rapid bursts of speciation.
Define ecotype
A population of microbes that’s genetically similar but ecologically distinct
Define a core genome (most conserved). Any variation in this genome is based on what?
The set of genes found in all members of a species; any variation in this genome is mutation-based.
Define pan-genome and name its 3 parts
1) The complete gene repertoire of taxon (all strains)
2) Core + ‘housekeeping’ + dispensable genes
Describe the 3 parts that make up the pan-genome of a species
1) Core: needed genes
2) ‘Housekeeping” genes: genes needed for normal growth and metabolism
3) Dispensable genes: extra genes you don’t need (genes for flagella, virulence factor genes, etc)
How is the pan-genome acquired?
By horizontal gene transfer (HGT)
1) What does horizontal gene transfer require?
2) What is the rate of transfer like in HGT?
3) What is HGT associated with?
1) Horizontal gene transfer requires a heterogeneous population
2) The rate of transfer is extremely variable
3) Associated with rapid adaptation to new environments
List and describe the 3 methods of horizontal gene transfer (HGT)
1) Conjugation: Physical connection between bacteria mediates transfer
2) Transformation: Uptake of naked DNA from the environment
3) Transduction: Viral transfer of DNA into bacteria
What 3 things is horizontal gene transfer important for?
1) Evolution
2) Adaptation
3) Pathogenicity
What 3 things can result from horizontal gene transfer (HGT)?
Gene acquisition, plasmid acquisition, phage infection
Describe the importance of Bergey’s Manual of Systematic Bacteriology
1) Contains descriptions of all known bacterial and archaeal species
2) An extremely valuable reference for microbiologists
