Bacteria and Archaea – morphologically simple,
metabolically diverse
Evolutionary relationships – the tree of life
Earliest organisms on earth resembled modern forms
Metabolic diversity  ecological diversity
A few cause diseases (+/- with humans)
Others provide services (+/+ with humans)
Critical for nutrient cycling
Eukarya evolved from symbiosis among prokaryotes
Earliest organisms on Earth
Diversification over
>3.5 billion years
soon after Earth’s origin
Earliest organisms on Earth
• early Earth was a hostile environment
• “oxygen revolution”
– early Earth’s atmosphere was anoxic
– cyanobacteria produce O2 as byproduct of photosynthesis
Prokaryotes
Eukaryotes
3.5 billion year old fossilized
filamentous cyanobacterium
modern stromatolites in
Western Australia
1
Characteristics:
Bacteria are
ubiquitous
Bacteria & Archaea
Unicellular
Prokaryotes (no membrane-bound nucleus)
Smaller than Eukaryotic cells
Domain Bacteria
Peptidoglycan cell walls
Plasma membrane similar to Eukarya
Unique ribosomes
Unique RNA Polymerase
Domain Archaea
Polysaccharide cell walls
Unique plasma membrane
Ribosomes similar to Eukarya
RNA polymerase similar to Eukarya
review Table 27.2 in textbook
Bacteria are
ubiquitous
Lyme disease
Yellowstone National Park
Hydrothermal vent
Metabolic diversity  ecological diversity
How do various organisms capture energy and carbon?
BACTERIA &
ARCHAEA
PLANTS
CHEMOSYNTHETIC
AUTOTROPHS
ANIMALS & FUNGI
How can prokaryotes thrive in so many environments?
2
Metabolic diversity  ecological diversity
A few bacteria are pathogenic
Tuberculosis
Lyme disease
Prokaryotes can use many energy sources in cellular respiration
Prokaryotes can metabolize many inorganic compounds (e.g., NH3, CH4, H2S)
Prokaryotes can ferment organic compounds other than sugar
 critical in decomposition (and stinky!)
Gastric ulcer
Photosynthetic prokaryotes – can use molecules other than H2O and O2
– several unique chlorophylls
Niche partitioning for light?
Borrelia burgdorferi
Mycobacterium
tuberculosis
Heliobacter
pylori
salt ponds
Many prokaryotes provide services
Extremophiles
bioremediation
• halophiles (e.g., salt flats)
dairy
products
• anaerobes (e.g. pluff mud)
nutrient cycling
hot springs
antibiotics
• thermophiles (e.g., hydrothermal vents)
bacterium from Yellowstone hot spring
Taq polymerase for PCR (polymerase chain reaction)
revolutionized the study of genetics
Thermus aquaticus
Why do astrobiologists study extremophiles?
3
Phylogenetic diversity of Bacteria
Ecological diversity in prokaryotes
cholera
anthrax
Lyme disease
leprosy
botox
Bern and Goldberg, 2005
BACTERIA
Phylogenetic diversity of Archaea
Cyanobacteria
thermophiles
~80 species, but very abundant
metabolize iron
(Ferroplasma sp.)
Misnomer “blue-green algae”
Nostoc sp.
Photosynthetic
Some colonial
halophiles
thermophiles
stromatolites are
living fossils
in symbiosis with fungi:
metabolize sulfur
Spirulina sp.
methanogens
4
Does metabolic diversity reflect phylogenetic diversity?
Does metabolic diversity reflect phylogenetic diversity?
Predict how metabolism maps onto the phylogeny
Independent evolution
of complex metabolic
pathways?
Lateral gene transfer
Major groups of Bacteria and Archaea
Some placement not fully resolved
Evolutionary relationships – the tree of life
Domain Eukarya
nuclear envelope
nucleus and organelles
complex cytoskeleton
cells usually larger than
prokaryotes
evolved from prokaryotes
5
Eukaryote innovations
Protists – paraphyletic and diverse
unicellular or multicellular
• complex cell structures
• sexual reproduction & multicellularity
Eukaryotes
sexual repro &
multicellularity
variation in cell covering
cell walls
shells
cell membrane
only
Ecological diversity of Protists
Protists – paraphyletic and diverse
pathogens
unicellular or multicellular
variation in cell covering
absorption
variation in feeding mode
ingestion
predators
primary
producers
African
sleeping sickness
decomposers and parasites
motility
photosynthesis
producers
How did eukaryotes
evolve from
prokaryotes?
cilia
flagella
predators &
filter feeders
Potato blight
decomposers
symbionts
How did plants, fungi
and animals evolve
from protists?
6
1. How did eukaryotes evolve from prokaryotes?
Inferred common ancestor of all modern eukaryotes:
BA
unicellular
membrane-bound nucleus
cytoskeleton
no cell wall
mitochondria
1. How did eukaryotes
evolve from prokaryotes?
B. EVOLUTIONARY INNOVATION:
Mitochondria
• site of cellular respiration
• double membrane
A. EVOLUTIONARY INNOVATION: Endomembrane system
•
•
•
Allows cells to be bigger
Surface area to volume ratio
Compartmentalization
– Endoplasmic Reticulum
– Golgi Complex
– Vacuoles
– Nuclear Membrane
1. How did eukaryotes evolve from prokaryotes?
• α-proteobacteria-like
• mutualistic, symbiotic relationship
Evolution of eukaryotes: membrane infolding and
endosymbiosis
C. EVOLUTIONARY INNOVATION: Chloroplasts
• site of photosynthesis
• double membrane
• cyanobacteria-like
7
2. How plausible is the Endosymbiosis Theory?
2. How plausible is Endosymbiosis Theory?
Evidence:
More evidence:
Traits shared by prokaryotes and mitochondria/chloroplasts:
Molecular (DNA) phylogeny: predict location of mitochondria and chloroplasts
• Circular DNA
• Divide by fission
• Small size
• Distinct ribosomes
Double membranes
Prochloron
Morphological similarity to cyanobacteria
Modern examples exist of protists with bacterial endosymbionts
What if mitochondria did not
arise via endosymbiosis?
Phylogenetic diversity of protists
Eight major, morphologically distinct groups
Does ecological diversity reflect
phylogenetic diversity?
Parasites
Malaria
Relationships among groups not completely resolved
Potato blight
Amoebic
dysentery
African
sleeping sickness
Intestinal
giardia
8
Does ecological diversity reflect
phylogenetic diversity?
Primary producers
Photosynthetic protists are not closely related
Dinoflagellates
Diatoms
Red
algae
PLANTAE
 Red Algae – most are multicellular
 Green Algae – unicellular, colonial, multicellular
STRAMENOPILA
 Brown Algae – multicellular
 Diatoms – unicellular or chains
“Algae” are
polyphyletic
ALVEOLATA
 Dinoflagellates – unicellular or colonial
DISCICRISTATA
 Euglenids – unicellular, also ingest food
Paraphyletic vs.
polyphyletic?
Euglena
How did this arise?
Green algae
Brown algae
3. How did photosynthetic eukaryotes evolve?
What are three hypotheses for the polyphyly of photosynthesis in protists?
1)
2)
Secondary endosymbiosis –
lateral transfer of chloroplasts among protists
3)
clue: some protist groups have chloroplasts with >2 membranes
solution: lateral transmission of chloroplasts = secondary endosymbiosis
9
4. How did large, complex organisms evolve?
Tree of life
or
web of life?
D. EVOLUTIONARY INNOVATION: Multicellularity
• differentiation among cells
• interdependent cells
Rare examples of cell specialization within bacterial colonies (δ-proteobacteria)
What two processes have
contributed to this pattern?
4. How did large, complex organisms evolve?
5. How did sexual reproduction evolve?
E. EVOLUTIONARY INNOVATION: Multicellularity
F. EVOLUTIONARY INNOVATION: Meiosis
fertilization = haploid  diploid
meiosis = diploid  haploid
haploid or diploid stage can be dominant
Alternation of generations –
multicellular haploid and diploid
How many independent origins of multicellularity?
10