Microbial Evolution and Taxonomy Flashcards
How old is the Earth?
~4.5 billion years old
When did water appear in liquid form?
~4.3 bilion years ago
When did microbial life begin?
~4.2 billion years ago
What are Stomatolites?
fossilized microbial mats - really thick layers of bacteria
How old are Stomatolites?
3.5 billion years old
Of what were ancient stromatolites made?
anoxygenic phototrophic filamentous bacteria
What is the Surface Origin Hypothesis?
- first membrane, self-replicating cells arose out of primordial soup rich in organic and inorganic compounds in ponds
- Against this hypothesis:
- dramatic temp flunctuations
- mixing from meteor impacts
- dust clouds
- storms
What is the Subsurface Origin Hypothesis?
- Life originated at hydrothermal springs on ocean floor
- conditions would have been more stable
- steady and abundant supply of energy (H2 and H2S) may have been available
What is the order in which biological entities formed?
- simple molecules
- hydrocarbons, sugars, fatty acids, amino acids, peptides, nitrogen bases
- RNA life
- RNA and proteins
- DNA
- LUCA - last universal common ancestor
- Diversification of molecular biology, lipids and cell wall structure
- early bacteria and early archaea
- Dispersal to other habitats
What is the RNA World Theory?
- proposes that RNA was first nucleic acid
- RNA can bind small molecules
- RNA has catalytic activity, may have catalyzed own synthesis
- DNA eventually became the genetic norm
- b/c its more stable
Metabolism of Primitive Cells
- chemolithoautotrophic
- Carbon from CO2
- energy from H2
When did the LUCA btwn Bacteria and Archaea diverge?
~3.8 billion years ago
When did cyanobacteria begin to generate O2?
~2.7 billion years ago
What is the Great Oxidation Event?
accumulation of O2 concentration to 1 part per million
When did the Great Oxidation Event occur?
2.4 billion years ago
Why did the O2 take so long to accumulate?
O2 had to react w/ FeS and FeS2 first
also O2 was gobbled up as soon as made at first
When did Eukaryotes first appear?
~2 billion years ago
What is the “Other Hypothesis” regarding the origin of eukaryotes?
- eukaryotes began as nucleas-bearing lineage that late aquired mitochondria and chloroplasts by endosymbiosis
What is the Hydrogen Hypothesis?
- eukaryotic cell arose from engulfment of a H2-producing cell of Bacteria by a H2-consuming cell of Archaea
- made mitochondria
- later formed nucleus
- formed chloroplast by endosymbiosis
Why is the Hydrogen Hypothesis more likely than the “Other Hypothesis?”
- eukaryotes have similar lipids and energy metabolisms to bacteria
- eukaryotes have transcription and translational machinery most similar to archaea
Phylogeny
- evolutionary history of a group of organisms
- inferred from nucleotide sequence data
- Assumptions:
- all organisms evolved from the LUCA
- DNA sequences represent a record of the organism’s ancestry
Molecular Clocks (chronometers)
- certain genes and proteins that are measures of evolutionary change
- need to be…
- functionally constant
- sufficiently conserved
- suffient length
- found in all domains of life
- need to be…
- most widely used ones are small subunit rRNA (SSU rRNA)
- 16S rRNA or 18S rRNA
- Assumptions…
- mutations occur at constant rate
- mutations are neutral
- mutations are random
BLAST (Basic Local Alignment Search Tool)
- alignment algorithm to compare sequence of interest to known sequences in database
What is the bacterial origin of mitochondria and chloroplasts?
Mitochondria arose from Proteobactreia
Chloroplasts arose from Cyanobacteria
What are the 2 major group of the Domain Archaea?
Crenarchaeota
and
Euryarchaeota
Taxonomy
the science of identification, classification, and nomenclature
Systematics
the study of the diversity of organisms and their relationships
links phylogeny w/ taxonomy
What is the definition of a prokaryotic species?
>70% DNA-DNA hybridization
>97% 16S rRNA gene sequence
share multiple phenotypes
FAME (Fatty Acid Methyl Ester)
analysis of fatty acids as phenotype analysis
variation in type and proportion of fatty acids present in membrane lipids
Multilocus Sequence Typing (MLST)
- method in which many diff “housekeeping genes” from an organism are sequenced
- recA and gyrB included
- very good specificity; very sensitive
Isolate
single clonal population w/ little genetic info known
Strain
single isolate or group of isolates w/ similar genetic/phenotypic traits that have been cultivated in the lab
Ecotype (Evocar)
population of cells that share a particular resource
Serotype (Serovar)
group of closely related microorganisms distinguished by characteristic set of outer membrane proteins
