Eukaryotic supergroups Flashcards
What are the 5 eukaryotic supergroups?
- Amoebozoa
- Archaeplastida (Algae and plants)
- Excavata (mostly heterotrophs, including pathogens)
- Opisthokonta (choanoflagellates, ichthyospora, metazoa, fungi)
- SAR (Stramenopila, Alveolata, and Rhizaria)
Evolution of multicellularity
- how many times has it happened?
- how many times has it led to COMPLEX multicellular organisms?
Multicellularity has evolved several times in the evolution of eukaryotes (at least 46 times).
However, complex multicellular organisms evolved in only 6 eukaryotic groups (animals, fungi, brown algae, red algae, green algae, and land plants
What are Opisthokonta?
Opisthokonta
▪ Includes both fungi and mammals, which are both independently evolved multicellular groups
Eukaryotic microbes key points
• Great majority of Eukaryotes are unicellular, a few large
multicellular groups:
– Metazoa; Plantae; & Fungi.
• Unicellular Eukaryotes are poorly understood and defined:
– however, they are ubiquitous, abundant and form a major part of the
biosphere.
• Eukaryotic innovations influence the biology of the organisms,
including:
– nutrition, locomotion, reproduction, and gene transfer.
• In addition to a wide variety of heterotrophic and phototropic
organisms, a number have evolved to be parasitic
– this includes a number of major pathogens of humans.
Eukaryotic innovations!!
• Have beating cilia
• Contractile vacuoles
- Regulates water quantity inside a cell
- Found mostly in protists and unicellular algae
• Food vacuoles
• Undulating membrane in groove (ciliary)
• Site of cell ‘anus’
- Excretion of waste material
• Macronucleus and micronucleus
- Macro is the centre of metabolic activity and micro is the storage site of germline genetic material
• Oral groove on surface
- Mouth of sorts, cilia beat food (bacteria) in
Distribution and diversity of eukaryotic microbes
• Mind boggling
• Over 250,000 species estimated to exist
- More than half represented in fossil record
- More than 10,000 are parasitic on other organisms
• Free-living single cell eukaryotes occupy every ecological niche
• Parasitic forms challenge a wide range of hosts
Nutrition of eukaryotes
• Most single celled eukaryotes are aerobic and respire
- Contain mitochondria or degenerate forms (mitosome, or hydrogenosomes)
• 2ndary characteristic – some are photosynthetic, containing chloroplasts
• Many are heterotrophic and absorb extracellularly digested food
• Some are predatory
Eg. amoeba and some ciliates like Paramecium
• A number are parasitic
Photosynthesis has been acquired on multiple occasions across the eukaryotes
Size and shape of eukaryotes
• V variable size (5-500um)
• Complex life cycles
- Some have two-phase life cycles eg. trophozoites and dormant cysts
• Absence of cell wall gives diverse morphology
• Instead of cell wall, Pellicle (flexible covering that gives the cell shape whilst permitting movement)
Excavata
phylum Euglena
- what
- where
- locomotion
o Genus of single cell flagellate eukaryotes
o Found in fresh and salt water
o 1/3 have chloroplasts and can photosynthesise
Locomotion
o Has a pellicle - flexible protein coat that allows cell to change shape
o Sliding of pellicle strips gives Euglena exceptional flexibility and contractility - can use to move by inching locomotion called ‘metaboly’
o Can also swim using flagella
o In low moisture conditions or when food is scarce, can form protective wall around itself and lie dormant as a cyst until conditions improve
Eukaryotic respiration variations
• Some have lost mitochondria but have other respiratory organelles
• Some parasitic species contain relic mitochondria – mito-like proteins that cluster together within a cell surrounded by small double membrane sacs
→ The presence of hydrogenosomes, mitosomes, and mitochondrial-like genes in the nucleus suggest mitochondrial loss rather than the amitochondriate eukaryotes being a pre-mitochondrial state
• Some have evolved a system of aerobic respiration that does not involve the mitochondria eg. Trypanosoma brucei kinetoplasts and glycosomes
What are mitosomes used for in Giardia?
Eg. Giardia
- Reproduce in the small intestines of several vertebrates, causing giardiasis
- Life cycle alternates between swimming trophozoite and cyst
- Mitosomes are not used in ATP synthesis like mitochondria, but instead are involved in the maturation of iron-sulfur proteins
- Mitisomes lack a genome and lost most mitochondrial functions
Kinetoplastida
• Kinetoplastida are a group of flagellated protists that have a kinetoplast (organelle containing many copies of the mitochondrial genome, located within the mitochondrion)
The glycolytic enzymes are held in membrane-bound glycosomes in trypanosomes such as Trypanosoma brucei (blood parasites)
Glycosomes are unique to kinetoplastids
• Glycosomes are derived from peroxisomes (organelles involved in breakdown of fatty acids, found in nearly all eukaryotic cells)
Name 5 means of eukaryotic locomotion
Eukaryotes have much more autonomy over movement than prokaryotes
Pseudopodia (false feet)
Eukaryotic Flagella
Eukaryotic cilia
Gliding locomotion
Pellicle ‘metaboly’ - inching along!! eg. Euglena
Pseudopodia (false feet)
- Temporary arm-like projection of a eukaryotic cell membrane
- Filled with cytoplasm, actin filaments and microtubules, which extend and contract
- Used for motility and ingestion
- Eukaryotes have actin which enables these structures to be formed!!
Eukaryotic flagella
• Used for rapid movement (planar and wave-like)
▪ ATP driven rather than proton gradient driven (in bacteria!)
• 9+2 microtubule axoneme
▪ Bundle of 9 fused pairs of microtubule doublets surrounding two central single microtubules
▪ Bending rather than rotary movement
▪ Bacterial flagella are single flagellin polymer, these are much more complex!!
• at the base is a basal body which is the microtubule organising center
• Flagella organelles associated with their own metabolism
• Flagella initiate signal-transduction cascades
Eukaryotic cilia
- Hair-like, occur in large numbers on cell surface
- Ultra-structurally identical to flagella although have different beating pattern
- Move like oars with alternating power and recovery strokes
- Generate force perpendicular to the cilia’s axis
- Synchronised beats (synchrony is v important)
- Generally faster compared with flagellates
- Move things along surface into ‘mouth’ (oral groove!!)
Eukaryotic gliding locomotion
• Independent of propulsive structures like flagella, pili and fimbriae
• Apicomplexan parasites include several significant pathogens eg. Plasmodium (malaria), Toxoplasma gondii (toxoplasmosis)
▪ They use a unique form of actin-based gliding motility to target and invade host cells
▪ This uses highly dynamic actin filaments
Give an example of an
- Amoebozoa
- Archaeplastida
- Excavata
- Opisthokonta
- SAR
Amoebozoa
Archaeplastida (Algae and plants) eg. Arabidopsis thaliana
Excavata eg. Euglena
Opisthokonta (choanoflagellates, ichthyospora, metazoa, fungi) eg. Homo sapiens
SAR (Stramenopila, Alveolata, and Rhizaria) eg. Eimeria (apicomplexan, Alveolata), TA
How do eukaryotes undergo asexual reproduction by binary fission?
- how do the cilia and flagella divide?
• Division into two ~equal parts, where cytoplasmic division follows mitosis
- The ciliates normally divide in an equatorial or transverse plane, maintaining the correct no. cilia.
- The flagellates normally divide in a longitudinal plane
• Amoebas have no fixed plane of division but simply round up and divide into two approx. equal halves
Name 3 asexual reproduction variations
• Endodyogeny
- Each DNA replication cycle is followed by mitosis and budding
- 2 daughter cells produced inside a mother, which is then consumed by the offspring
- Done by T. gondii
• Leukocyte transformation
- Sporozoites infect leukocytes, transform them and divide by exploiting the mitotic and cytokinetic machinery of the host wbc
• Schizogony
- Nuclei initially multiply by asynchronous rounds of mitosis
- The last round is synchronous for all nuclei and coincides with budding at the parasite surface
• Endopolygeny
- DNA replicates without nuclear division, using multiple synchronous mitotic spindles
- The final mitotic cycle coincides with budding and the emergence of a new generation of merozoites
Sexual reproduction by conjugation
- Evolved as a consequence of increased size and complexity
- No increase in numbers, just genetic exchange
- Micronucleus undergoes meiosis (can replicate by mitosis to give a no. haploid nuclei)
- Bridge of cytoplasm forms and one haploid nucleus is exchanged with the partner
- Nuclear fusion, diploid restored
- Old macronucleus disintegrates
- Mitosis of “new” micronucleus, one converts to macronucleus
Eimeria life cycle
EXOGENOUS PHASE
❖ Infected host releases oocysts into environment
ENDOGENOUS PHASE
where the parasite development occurs in the host intestine (several rounds of asexual reproduction by schizogony, sexual differentiation of gametes, and fertilisation)
❖ When ingested, sporulated oocysts undergo MITOSIS, each release 4 sporocysts in the stomach, which each release 2 sporozoites into the intestine
❖ Gliding motility allows attachment to host cells
❖ After invasion, sporozoites develop into trophozoites (feeding stage), then schizonts
❖ After 3 or 4 rounds of schizogony, there are many nuclei developing within the schizont
❖ Each nuclei develops into a merozoite
❖ Schizonts rupture, releasing merozoites which differentiate into male/female gametes (gametogony)
❖ Gametes fuse (fertilisation), and and zygote formation triggers formation of the oocyst wall.
❖ oocyte is released in its non-infectious, unsporulated form through host faeces
Importance of parasitic diseases
Socio-economic
- Protozoan parasites often affect the poorest people
- Obstacle to economic and political development
- Huge financial loss – more than $12 billion lost per year in Africa to malaria alone (Plasmodium-caused)
Medical
- Parasites cause common human infections, especially a problem in the developing world
Biological
- Unique organelles and biochemistry
- Raise evolutionary questions
- Complex life cycles and transmission patterns (cestode worm and three-spined stickleback!)
- Diverse host-pathogen interactions
Eukaryotic pathogens
- examples
Eukaryotic pathogens include:
Protista (single celled eukaryotes) eg.
Plasmodium/malaria
Fungi eg. Candida albicans/thrush
Animalia
o Schistosomiasis (trematode flatworms)/ parasitize humans and snails
o Arthropod vectors eg. mosquitos/Zika, fleas/Plague
What is Eimeria?
- why is it important to know about it and understand it?
Eimeria
• Apicomplexan parasite (SAR)
• Affects almost all vertebrates eg. cattle, poultry, fish
• As few as 50,000 infective oocysts can cause severe disease in a young calf
Impacts on global food security, act as reservoirs for human infection, harm animal welfare
Apicomplexans
- SAR, Alevolata
- Phylum of obligate parasitic protozoa, eg. T. gondii, Plasmodium, Eimeria
• Contain a unique form of organelle called an apicoplast
- Apicoplast is a degenerate chloroplast, and is no longer capable of photosynthesis
- Results from secondary endosymbiosis of cyanobacteria
- No flagella or cilia - they use a unique form of actin-based gliding motility to target and invade host cells
- Food taken up in soluble form across the cytoplasmic membrane
- Sexual & asexual reproduction
- Produce sporozoites (spore-like bodies) which function into transmission to new host
- Named after the apical complex (collection of organelles involved in attachment and invasion of host cells)
Toxoplasma gondii
- why is it important to know about it and understand it?
Toxoplasma gondii
• Obligate intracellular single celled parasite, apicomplexan!!
• Causes infectious disease toxoplasmosis
Definitive host - Felids (eg. domestic cats) are the only definitive hosts
Intermediate hosts - can be many warm blooded species (including humans)
Can cause significant damage to foetuses in pregnant women
Features of eukaryotic parasitic diseases
• Euk pathogens can have complex lifecycles with both sexual and asexual phases
• Capacity to produce resting stages
- For example, very resistant spores
• Euk.s separate growth from reproduction
→ They can have much larger genomes
→ More elaborate systems
→ Life cycle can accommodate multiple hosts
• Diverse means of locomotion & spread
• Transmission routes:
- Faecal-oral eg. T. gondii, Eimeria
- Sexual
- Vectors (mostly insects) eg. Plasmodium
• High mortality of offspring result in strategies to produce lots of them
Life cycle stages of eukaryotic parasitic diseases
Life cycle stages
1. Sporozoite
❖ Motile, spore-like stage
❖ Develop into trophozoites
2. Trophozoite
❖ Intracellular feeding stage before schizogony
3. Merozoite
❖ Develop from asexual reproduction within the schizont
❖ Released and develop into male/female gametes
Name 3 eukaryotic pathogens that have faecal-oral transmission
- Eimeria
- Toxoplasma gondii
- Giardia intestinalis
Challenges of faecal-oral transmission
• Challenges:
- Need to resist the environment (cysts or oocysts)
- High parasite losses so need high no.s
- Need a way of sensing entry into host
- Host availability can be problematic
Advantages of faecal-oral transmission
• Advantages
+ adaptation focussed on single host type
+ ease of entry into the host by ingestion (bypass barriers like skin)
+ can remain metabolically inactive in environment (increases survival chances)
Name 3 methods human intestinal parasites use to invage
They invade in v different ways
- secreting proteins
- using attachment discs
- gliding motility
aiding attachment
Why are cysts hard to prevent?
resistant to conventional water treatment methods such as chlorination
Giardia intestinalis
Giardia intestinalis
- Causes giardiasis, which can range from asymptomatic to severe diarrhoea and vomiting
- Infection can occur through ingestion of cysts in contaminate water or food or by the faecal-oral route
- Reproduce in the SMALL INTESTINES of several vertebrates, causing giardiasis
- Trophozoites swim through intestinal mucus, then use an adhesive disc to attach to the host intestinal epithelium
- Remains confined to the lumen of the small intestine, where trophozoites absorb their nutrients and then undergo ASEXUAL REPRODUCTION by binary fission
- Then produce cysts which are expelled in faeces
G. intestinalis are flagellated, have two nuclei of equal size, and contain mitosomes instead of mitochondria (not used in ATP synthesis like mitochondria, but instead are involved in the maturation of iron-sulfur proteins)
Name 3 eukaryotic pathogens that have invertebrate vector transmission
- Plasmodium spp. (mosquitos, malaria)
- Trypanosoma brucei (Tsetse flies, sleeping sickness)
- Leishmania spp. (Sandflies, leishmaniasis)
Challenges of invertebrate vector transmission
- Needs to adapt to multiple hosts (and their differing immune responses)
- Needs a way of transferring between hosts
- Needs a way of sensing change of host to change strategies
- Host availability/lifespan can be problematic
Advantages of invertebrate vector transmission
+ invertebrate host provides protection from the environment
+ ease of entry by injection into a wound (use insect biting parts to get into wound – host manipulation!!)
+ vector-based dispersal (malaria has wings!)
+ vector-based host selection
Life cycle of plasmodium falciparum
- Mosquito injects sporozoites into bloodstream when it bites human
- Sporozoites travel to liver and take residence in hepatocytes
- Sporozoites multiply asexually into schizont, which ruptures, releasing merozoites back into the bloodstream
- Merozoites invade erythrocytes, forming ring-like trophozoite.
- The ring stage trophozoites multiplies asexually to form schizonts, which rupture releasing merozoites when rbcs burst
- This cycle of rbc invasion, multiplying and bursting continues, causing malarial symptoms such as chills and sweating
- After several asexual cycles, the merozoites will form gametocytes when it infects a rbc
- Gametocytes sucked up by another mosquito, digesting the gametocytes and allowing them to mature into gametes, which fuse together to form oocyte
- Oocyst develops sporozoites which are released when oocyst ruptures
- Sporozoites migrate to mosquito’s salivary glands
Malaria symptoms
fevers and chills, headache, vomiting, neurological symptoms
African trypanosomes
Trypanosoma brucei
SLEEPING SICKNESS
- Free-living (extracellular) parasite carried around in bloodstream of infected hosts
- One of the few pathogens to cross the blood brain barrier
- Carried by Tsetse fly vector between mammal hosts
- Flagellated (9+2)
- Has an unusual organelle called a kinetoplast made up of many copies of the mitochondrial DNA
- Have glycosomes (membrane bound organelles containing the glycolytic enzymes) which are derived from peroxisomes
How do they reproduce?
• In mammal BLOOD & and LYMPH, grow long and thin and multiply by binary fission, penetrate blood vessel endothelium and invade tissue including CNS
• In fly, multiply and enter salivary glands
How does Trypanosoma evade the immune system & and maintain chronicity?
Trypanosoma
• Have surface glycoprotein – express VSG (variant surface glycoproteins)
• Able to make new VSGs from library of genes they have – great way of achieving promiscuity
Symptoms of sleeping sickness
Symptoms:
- Haemo-lymphatic stage causes fever, headaches, joint pain
- Neurological stage when parasite infects CNS
- Changes of behaviour, confusion, poor coordination
- Usually fatal without treatment
Conclusions from eukaryotic pathogens
• Parasites remain significant causes of morbidity and
mortality
– Impact especially great in low income countries.
• Parasite biology enables complex lifestyles and
relationships with, sometimes multiple, hosts
– Widespread occurrence of dormant resistant forms;
– Some organisms have evolved mechanisms of immune evasion.
• Public health interventions are often complicated and
expensive (no vaccines!).
