Three Domains of Life
Protists
Three Domains of Life
Changes in Classification
• The ‘old school’ method of classification
included 5 Kingdoms (what I learned in school)
– Monera
– Protista
– Fungi
– Plantae
– Animalia
• Today, advances in molecular technology
expanded our understanding (and
interpretation) of systematics
Modern Systematics
• Three Domain classification of life
• Numerous, virtually countless Kingdoms
• Bacteria and Archaea are now 2 distinct
Domains (once included together in
Kingdom Monera)
• Protista, Fungi, Plantae, and Animalia
remain classified as distinct Kingdoms,
although classification of the kingdom
Protista has been met with complications
Prokaryotes
• Includes the kingdoms Archaea & Bacteria
• Oldest, structurally-simplest, and most
abundant forms of life
• Photosynthesis  Bacterial and
Eukaryotic Diversity
• Important decomposers and symbionts
Prokaryotes
• Unicellular
• Typically 1μm or less (1000 μm = 1mm;
1000mm = 1 meter)
• No membrane-bound nucleus; instead a
single circular chromosome made of DNA
• Asexual reproduction by binary fission
• Photosynthetic bacteria utilize oxygen or
chemical compounds, such as sulfur
Prokaryotic Cell Structure
• Three basic forms:
– Bacillus – rod-shaped
– Coccus - sphercal or ovoid-shaped
– Spirillum – spiral or helical
Prokaryotic Cell Structure
• Prokaryotes have a tough cell wall and
other external structures
• Cell wall consists of peptidoglycan; a
rigid network of polysaccharide strands
cross-linked by peptide side chains;
unique to Bacteria
• Maintains the shape of the cell and
protects it from swelling and rupturing
• Prokaryotes can have
1 or more flagella
(much less complex
than in Eukaryotes)
• Some Prokaryotes
possess pilli,
which helps
fasten cell to host
membrane
Domain Archaea
• Once considered a subdivision of the
Kingdom Monera, now its own domain
• Like all prokaryotes, Archaea are singlecelled microorganisms that lack a nucleus
and membrane-bound organelles
• Best known for the “extremophiles” –
Archaea which thrive in extremely harsh
environments
Archea - Extremophiles
• Thermophiles – thrive at
60-80°C (>176°F!)
• Acidophiles – thrive at
pH at or below pH 3
• Xerophiles – grow in
extremely dry conditions
• Halophiles – require
extremely high
concentrations of salt
http://www.dpchallenge.com/image.php?IMAGE_ID=448561
Archaea - Extremophiles
• Evidence for evolution of life on Earth?
• Many of the harsh conditions which
extremophiles require to survive were
characteristic of our early Earth
• Likely that extremophiles evolved to dwell
in such conditions billions of years ago
and retained ability to survive today in
specific environments
• Archaea differ from Bacteria in numerous
ways
– Plasma membranes are made of different
kinds of lipids
– RNA and ribosomal proteins more like those
of Eukaryotes
– Mostly anaerobic
Photosynthetic
Domain Bacteria
• Two types:
– Gram-positive
– Gram negative
• Refers to the Gram Stain (purple dye)
• Gram-positive bacteria – possess a thicker
peptidoglycan cell wall; retain stain
• Gram-negative bacteria – contain less
peptidoglycan; do not retain stain
Gram-positive and negative
Bacterial Conjugation
• Transfer of genetic material
• Horizontal gene transfer
• NOT sexually (no gametes)
Eukaryotic origin
• The nucleus and
endoplasmic
reticulum arose from
infolding of the
prokaryotic cell
membrane
Eukaryotic origin
• Eukaryotic organelles arose from a
consortium of symbiotic prokaryotes
– Mitochondria were aerobic heterotrophic
prokaryotes
– Chloroplasts (for photosynthesis) were
photosynthetic prokaryotes
Endosymbiotic theory
• Evidence?
– Mitochondria have their own independent
DNA, and a double membrane
– Chloroplasts resemble cyanobacteria; also
have their own independent DNA and a
double membrane
Kingdom Protista (the trouble-maker)
• Kingdom Protista is NOT monophyletic
Paraphyletic –
includes common
ancestor but not
all descendents
Kingdom Protista
• Eukaryotic (must be! Domain Eukarya)
• Largely unicellular with some multi-cellular
‘exceptions’ (e.g., kelps, seaweed)
• May be autotrophic or heterotrophic
• Debate over classification –
– Are some protists members of other kingdoms?
– Would protists best be considered as several
different kingdoms?
Kingdom Protista
• Characterized by:
– Mode of locomotion (e.g., flagella, cilia)
– Mode of nutrition (e.g., autotrophic,
heterotrophic)
– Body form (unicellular, multicellular)
– Pigmentation (e.g., Red, Green, Brown alga)
– Reproduction (asexual, sexual)
• Multicellular protists are distinguished from
other Kingdoms by their lack of specialized
tissues
Kingdom Protista
Kingdom Protista
• Have you ever eaten
a protist?, or should I
ask, have you ever
eaten seaweed???
• Just to complicate
matters, green algae
is categorized as a
plant in Kingdom
Plantae…
Green Plants evolved from Green
Algae
• We’ll come back to this…
Kingdom Fungi
Kingdom Fungi
•
•
•
•
•
Unicellular and multi-cellular
~1.5 million species
Important decomposers
Includes many disease-causing organisms
Others are important symbionts and
fermenting organisms
Kingdom Fungi
• Mycology – the study of fungi
• All fungi are heterotrophic
– Obtain their food by secreting digestive
enzymes and absorbing the nutrients
released by the enzymes
• Unicellular fungi may have flagella;
multicellular fungi are primarily filamentous
in form
• Cell walls composed of chitin
Kingdom Fungi
• Six phyla
– Cytrids (flagellated), Zygomycetes (inc. bread
molds), Glomeromycetes (mycorrhizae),
Ascomycetes (inc. yeast), Bascidiomycetes
(mushrooms), and Deuteromycetes (not pictured)
Kingdom Fungi
• Phylogeny based on the 5 major Phyla
(based on mode of sexual reproduction)
Kingdom Fungi
• Multicellular fungi consist of long, slender
filaments called hyphae
• Some hyphae are
continuous; others
are divided by
septa
• Mycelium – a
mass of
connected hyphae
Kingdom Fungi
• Mycelium grows through and digests its
substrate
• Fungi live in their food!
Kingdom Fungi
• Hyphae (mycelium) form complex
structures
• A mushroom is a spore-bearing body of a
fungus; composed of hyphae
• A puffball is a spore-bearing body of
certain species of fungi, including the
deadly Death Cap mushroom; composed
of hyphae
Kingdom Fungi
• Fungi can also be monokaryotic or
dikaryotic
– Monokaryotic – one nucleus per cell
– Dikaryotic – two nucleii per cell
• Fungi reproduce sexually and asexually
– During sexual reproduction in some fungi, 2
haploid nuclei fuse creating a dikaryotic
(dikaryon) stage, which precedes the normal
diploid nucleus
Kingdom Fungi
• Some fungi produce specialized mycelial
structures to house spores (e.g.,
mushroom, puffballs, ‘shelf’ mcycelium on
dead trees)
• Spores can form as a result of sexual or
asexual reproduction
• Spores can withstand degradation and
survive for long periods of time; because
of their size, they can travel long distances
Kingdom Fungi
• Chestnut Blight – a fungal disease which
has virtually eliminated the American
chestnut
• Accidentally introduced into the U.S. on
imported lumber from Asia
• The roots of the tree are fairly resistant to
the fungus, but the tree succumbs once it
grows enough shoots to reproduce
• Unknown spreading agent (the spores are
everywhere!)
Kingdom Fungi
http://www.kychestnut.org/images/openGrownTree.jpg
…Jack Frost nippin’ at your
nose…
• The American chestnut once covered
large tracts of forest in the U.S.
• The chestnut was a very important
source of food for wildlife (and the
inspiration for at least 1 Christmas
song…)
• At the turn of the twentieth century, one
quarter of all trees in the eastern United
States were chestnut!
The Chestnut Blight
• Only a few mature survivors remain of the
American Chestnut, which once consisted
of 4 billion trees (that’s over 99.99% gone)
• If you have ever eaten a chestnut, you had
a European import; only our grandparents
may have ever tasted an American
chestnut
• The American Chestnut Foundation seeks
to restore the great chestnut, but how?
The Chestnut Blight
• Development of blight-resistant American
chestnuts is accomplished through a
process known as “backcross breeding”
• Hybrids between American and Chinese
chestnuts are repeatedly crossed back
onto purely American specimens, yielding
offspring which are blight- resistant
• The resulting offspring are ~94% American
(6% Chinese) and disease-resistant
Kingdom Fungi
• Spores are frequently dispersed by wind,
but may also be spread by insects and
small animals
• Chytrids are an ancestral group and retain
flagella; have motile zoospores
Why did the mushroom go to the party?
• Many fungi live underground, and can
reach great sizes
• One of the largest living organisms in the
world is a fungus!
• The largest known specimen covers more
than 3.4 square miles and is thousands of
years old
• And some species of fungi are
bioluminescent!
Armillaria fungus
• Connected underground by hyphae!
Fungal Ecology
• Fungi often have interactions or
symbioses with other organisms
• Obligate symbiosis – essential for survival;
fungus cannot survive without symbiont
• Facultative symbiosis – fungus can survive
without symbiont
• Mutualistic relationships – both partners
benefit
• Commensal relationships – one partner
benefits, but the other is unaffected
Fungal Ecology
• A lichen is a symbiotic association
between a fungus and a photosynthetic
partner (usually green algae or
cyanobacteria)
Fungal Ecology
• Mycorrhizae – association between a
fungus and the root of a tree
• Mycorrhizae function as an extension of
the plant root system; the fungus
increases surface area for absorption and
aids in transfer of nutrients
• The plant, in return, supplies organic
carbon to the fungus
Mycorrhizae
• Very important!
• Mycorrhizal plants are more resistant to
drought and even microbrial soil-borne
pathogens
• Two types
– Arbuscular mycorrhizae
– Ectomycorrhizae
Mycorrhizae
Fungal Ecology
• Leaf-cutter ants – an animal
symbiont with fungi!
• The ants feed on special
structures produced by a
fungus that they have
domesticated
• The ants feed the fungus
leaves and protect it from
pests and molds
• In return, the ants eat the
fungus and feed it to their
young
Just in case you didn’t believe me…
http://www.flickr.com/photos/kellyslittlepieces/2243322652/