Chapter 16 Flashcards
Early Earth
Forma5on of earth—4.5 bya
• Microbial life—found in fossils 3.5 billion years old
Stromatolites
Microbial mats
of layers of filamentous
microbes and minerals
Subsurface origin of life hypothesis
Life originated at hydrothermal springs on
ocean floor • Stable condi5ons
• Steady and abundant supply of energy (e.g., H2
and H2S)
RNA world and lipid vesicles
RNA world theory
– RNA can bind small molecules (e.g., ATP, other nucleo5des)
– RNA has cataly5c ac5vity; may have catalyzed its own synthesis
• Lipid vesicles
Last universal common ancestor (LUCA)
Possible scheme for energy genera5on in primi5ve cells
Abundant H2 and FeS
Endosymbio5c hypothesis
Mitochondria and chloroplasts of eukaryotes arose from engulfment of bacteria into other cells
• Prokaryo5c ribosomes (70S) • Bacterial 16S ribosomal RNA • Ribosomes inhibited by same an5bio5cs • Covalently closed, circular DNA
Endosymbio5c hypothesis #2—hydrogen hypothesis
Accounts for • Bacterial lipids • Archaeal
transcrip5on and transla5on
• Bacterial energy genera5on
• Favored hypothesis
Evolu5on
Descent with modifica5on
Fitness
survival capacity or reproduc5ve ability
– Harmful muta5ons—lower fitness – Beneficial muta5ons—increase fitness – Neutral muta5ons—do not affect fitness,
accumulate in genome
Gene duplica5on • Gene loss
obligate symbionts and parasites • Horizontal gene transfer
Environments select organisms that
survive and successfully compete and reproduce
Evolution occurs rapidly in microbes because of
Large popula5ons – Fast reproduc5on
Phylogeny
Inferred evolu5onary history • Assump5ons:
– All organisms descended from LUCA – Sequence of DNA is record of organism’s ancestry
Genes used in phylogene5c analysis
Small subunit rRNA (SSU rRNA)
– 16S rRNA in prokaryotes – 18S in eukaryotes
– Universally distributed – Func5onally constant – Sufficiently conserved
– Adequate length
Genes used in phylogene5c analysis
EF-‐‐Tu• Hsp60 • tRNA synthetases
• gyrB • recA
Molecular clocks
assumes that changes accumulate at a constant rate, are neutral, are random—combine data with geologic evidence
Evolu5onary analysis
Obtain sequences through PCR
– Oligonucleo5de primers
Microbial systema5cs
Iden5fica5on of new bacterial species:
– Genotypic—gene sequences – Phylogene5c—evolu5onary framework
– Phenotypic—morphological, metabolic, physiological, and chemical characteris5cs
Biological species concept
Interbreeding popula5on of organisms that is reproduc5vely isolated from other interbreeding popula5ons
– Not valid for haploid organisms
Phylogene5c species concept
Group of strains that cluster closely with each other and are dis5nct from other strains
Ecotype
cells in a popula5on that
share a par5cular resource
Prokaryo5c species
Defined as strains with
– 70% or greater DNA-‐‐DNA hybridiza5on – 97% or greater iden5ty in 16S rRNA sequence
• Over 7,000 known species of Bacteria and Archaea
• Possibly up to 100,000 species
Binomial system of nomenclature
Carl Linnaeus • Genus names and species epithets • La5n or La5nized Greek deriva5ons • Italicized • Staphylococcus aureus means “a bunch of
grapes”, “berry”, and “golden”
• IJSEM approval required
