Lecture 4 - protists, including eukaryotic parasites Flashcards
what is a protist?
any eukaryote that is not an animal, plant or fungus
total biomass is twice that of animals
mostly unicellular
some form colonies with one or two types of cells
a few are multicellular (some brown & red algae)
how are protists diverse?
protists represent the main diversity of eukaryotes
historically ancient
live in virtually all niches on Earth
mostly microscopic but span 6 orders of magnitude
can be smaller than bacteria…..
…..or taller than a 10 storey building
can exist as solitary cells or as giant colonies
can be purely phototrophic (algae) or heterotrophic (protozoa) or mixotrophic
abundance
algal blooms can be seen from space
few abundant species, many more rare species
rare biosphere
numerous rare protists (high microbial richness but low species abundance)
only appreciated as sequencing methods have improved
important roles e.g. specific biochemical activities, or can increase in abundance in certain situations, deep-branching phylogenetic diversity?
what are their importance?
of critical ecological, biogeochemical & medical importance
primary producers & food chain intermediates
phytoplankton (diatoms & dinoflagellates plus cyanobacteria) account for ~50% photosynthetic activity globally & >50% oxygen production despite only accounting for 1% global plant biomass
base of marine & freshwater food webs & key parts of these ecosystems
biogeochemical cycles e.g. carbon, silicon, strontium
biomonitoring
absorption & bioaccumulation of heavy metals
symbiotic partners
medically & ecologically important parasites
whart is the marine carbo pump?
Protists fix carbon
CO2 by phototrophs into organic matter (photosynthesis)
carbonic acid/carbonates incorporated into CaCO3 shells (foraminifera & coccolithophores)
Protists sink (eg if dead) or migrate to ocean floor & sequester carbon
what are the diatom properties?
phytoplankton – aquatic algae
stramenopiles
major marine producers
produce 20-50% Earth’s oxygen
contain yellow-brown chloroplast
major role in carbon cycle
fix 20% global CO2
transparent silica cell wall – frustule
highly intricate patterns & topology
pennate (pen-like) or centric (cylindrical)
2 valves, one fitting inside the other
how do diatoms reproduce?
Asexual and sexual reproduction of a centric diatom. Diploid forms dominate – unusual for algae. The diatom shell (frustule) is composed of two valves which fit together like a box with a lid. During asexual reproduction the two valves separate with each valve becoming the new “lid” of the daughter cell leading to a decrease in size of the population over time. Once a size threshold is reached, initial cell size is restored by sexual reproduction during which haploid gametes fuse to produce zygotes that develop into auxospores. Graphic taken from Kale and Karthick (2015).
how do you exploit diatoms?
Bind & accumulate metals
precious metals - gold & silver nanoparticles
catalysis, biological labelling, drug delivery, cancer therapy, anti-microbials, data storage, chemical sensing
toxic metals e.g mercury, cadmium
Biosensors
some species more tolerant than others
shrink in size/change shape/die in response to toxic conditions
what are dinoflagellate properties?
mostly marine organisms, some freshwater
about half are photosynthetic & have chloroplasts
autotrophic or mixotrophic
3 membranes surrounding chloroplast – originated from ingested alga
rest are heterotrophic
some get food via phagocytosis of ciliates & metazoans
may contain cyanobacteria for nitrogen fixation
can migrate vertically through water
to maximise exposure to light for photosynthesis
to find food (prey or nutrients)
what is the cell structure of dinoflagellates?
alveolate
cortical alveoli in plasma membrane
in armoured forms, alveoli contain cellulose plates (theca) impregnated with silica
2 flagella
transverse & longitudinal flagella
spinning top motility
nucleus with permanently condensed chromosomes
liquid crystal structure
few histones & other DNA- binding proteins
how do dinoflagellates sense light?
some dinoflagellates (warnowiids) have ocelloid structures
analagous to eyes
thylakoid membranes & light- sensitive protein (retinal body, from red alga), reconfigured mitochondrion (cornea) + lens & iris
less complex eyespot apparatus in other dinoflagellates
what is the ecology of dinoflagellates?
Blooming
rapid replication if nutrients are abundant
red tides
toxins – fatal to fish & dangerous to consumers of fish e.g. shellfish poisoning
Bioluminescence
emit blue-green light when disturbed
luciferase & luciferin present in cytoplasmic scintillons that move to cell periphery in the dark
may be defense mechanism against predators
Dinoflagellates – endosymbionts & hosts
zooxanthellae e.g. Symbiodinium in cnidarians (coral & jellyfish), sponges, molluscs, protists
stresses can lead to expulsion of dinoflagellates & coral bleaching
some dinoflagellates host other symbionts
Kryptoperidinium - diatoms
Noctiluca - green alga
what is radiolaria?
marine protists
polar regions to tropics
upper sunlit layers to deep sea
intricate biomineralized skeleton
mostly shells, but also spines & spicules
mostly opaline silica (SiO2 nH2O)
Acantharia – strontium sulphate
some naked species (Collodaria) can form large (3m) colonies
skeletons of dead protists sink to seabed & are incorporated into sediments & rock – fossils & radiolarian ooze
important for carbon & silicon cycles & strontium budget
phagotrophs – pseudopods – capture range of prey
some harbour photosymbionts (prokaryotes to dinoflagellates)
what is foraminifera?
mostly marine
benthic (sea bottom)
planktonic (floating)
some species have algal endosymbiont
some parasitic e.g. to sponges & coral
granular streaming pseudopodia
locomotion, attachment, food, digestion, shell construction
external shell or test
mostly CaCO3 or agglutinated sediment particles, rarely silica & some primitive ones made of chitin
usually < 1mm, but some 20 cm
fossil record & bioindicators
help to find hydrocarbon deposits
CaCO3 shell susceptible to acidic conditions – helps to monitor coral health
what are Coccolithophores
calcifying algae from Haptista
coccolithogenesis – production of CaCO3 scales
coccosphere may provide viral protection
50% pelagic CaCO3 sediments
compacted to form chalk
Emiliania huxleyi
most abundant coccolithophore
accounts for 1/3 total marine CaCO3
forms seasonal algal blooms
collapse after 5-8 days due to infection with EhV giant virus
photosynthetic, 2 brown chloroplasts, sunlight zone of ocean
1-10% primary production
what is green algae
Chloroplastida
single cells, colonies, long filaments, macroscopic seaweeds
green algae = symbionts of ciliate Paramecium & flatworms
dinoflagellates contain chloroplasts ingested from green algae
symbioses with fungi - lichens
what is red algae?
Rhodophyta
mostly multicellular & macroscopic
marine, freshwater & extreme habitats
no flagella or centrioles
chloroplast - >half microbial eukaryotes have red algal-derived plastid
coralline algae secrete CaCO3 & build coral reefs
what are the natural properties of algae?
Algae are highly nutritious
protein, carbohydrates, lipids, polysaccharides, dietary fibre, omega-3 fatty acids, vitamins & minerals/elements, pigments
antioxidant, antibacterial, antiviral, antifungal properties
neutraceuticals
Alginates (brown algae) & carrageenans (red algae)
act as thickeners, gelling agents & stabilisers
Nori seaweed
source of iodine
Animal & plant feed
Astaxanthin from Haematococcus pluvialis
how is algae used?
diatomite/diatomaceous earth
filtration aid, mild abrasive e.g. toothpaste, cleaning products, insecticide, cat litter, stabilising agent in dynamite (mixed with nitroglycerin)
production of biofuels
commercial viability issues
cosmetics
additives, stabilisers, active ingredients
biodegradable food containers, bioplastics, foams
agar – red algae
mix of agarose + agaropectin
food grade agar – mainly agarose
what are Apicomplexan diseases - malaria
241 million cases, 627,000 deaths, mostly in children in Africa (2020)
Plasmodium spp.
transmission: Anopheles mosquitoes
febrile/flu-like illness
anaemia, jaundice, kidney failure, seizures, confusion, coma, death
pregnant women at higher risk of serious disease
what are Toxoplasmosis?
up to half world’s population infected + most warm-blooded animals
Toxoplasma gondii
transmission: eating undercooked infected meat, cat litter trays, gardening, congenital
mostly mild flu-like illness
more serious or fatal if immunosuppressed or infected congenitally
what are Apicomplexans?
single copy organelles
nucleus
mitochondrion
apicoplast –
from secondary endosymbiosis of red algae
essential but no longer photosynthetic
secretory organelles
rhoptries, micronemes & dense granules
cell division structures
centrosome, basal complex
complex cytoskeleton
inner membrane complex = 2 layers of alveoli & subpellicular microtubules, covered by plasma membrane
what are types of neglected tropical disease?
Chagas disease
Trypanosoma cruzi
transmission: reduviid bugs, food, blood products, congenitally, transplants
6-7 million infected, mostly in Latin America
acute phase, becomes chronic if untreated – 30% develop cardiac issues, 10% digestive problems
Leishmaniasis
Leishmania spp.
transmission: phlebotomine sand flies
700,000-1 million new cases/year
visceral disease – 95% fatal if not treated
cutaneous disease – scars, stigma, disability
Sleeping sickness/Nagana (human/animal African trypanosomiasis)
Trypanosoma brucei (HAT & AAT); T. congolense & T. vivax (AAT)
transmission: Glossina tsetse flies in sub-Saharan Africa
663 cases HAT reported in 2020
AAT now the bigger problem
what are T. brucei
single copy organelles
model organism
flagellum biogenesis/ ciliopathies
Golgi biogenesis
RNA editing
GPI anchors
what are Giardia?
anaerobic diplomonad
Giardiasis - diarrhoea
faecal-oral transmission
8 flagella
2 nuclei
reduced mitochondrion – mitosome – no genome, Fe-S cluster assembly
no Golgi
cytoskeleton - median bodies & axostyle
ventral disc
what are Trichomonas?
anaerobic parabasalid
trichomoniasis – STD: itching, pain, swelling, discharge, increased risk of HIV infection, abortion in cattle
5 flagella
1 nucleus
no mitochondria - hydrogenosomes – double membrane, no genome, ferment pyruvate to produce ATP & H2
parabasal complex – Golgi + filaments
cytoskeleton – axostyle, costa
what are TSARs?
telonemids, stramenopiles, alveolates, rhizarians
comprise up to half of all eukaryotic species diversity
