eukaryotic microbes Flashcards
explain the main features of protozoa
- single-celled
- lack a rigid cell wall
- usually motile
- inhabit a ‘wet’ environment
- may form a resting stage comprising of spores or cysts
- heterotrophs
explain the main features of algae
- essentially protozoa with a plastid
- organisms in which the plastid is a chloroplast are phototrophs
what does Leishmania cause?
leishmaniasis
what does Phytophthora infestans cause?
potato blight
what does Phytophthora palmivora cause?
blight of cocoa pods
what do dinoflagellates cause?
red tides
which organism gave rise to the white cliffs of Dover and how?
Emiliana huxylei
CO2 —> CaCO3 + C6H12O6
how have eukaryotes evolved from prokaryotic Archaea?
- internal membrane formation
- cell enlargement
- serial endosymbiosis
give examples of prokaryotes that have eukaryotic features
Gemmata obscuriglobus has a nuclear envelope
cyanobacteria have thylakoid membranes
which organisms were the precursors of eukaryotes?
protoeukaryote, early α-proteobacterium, early cyanobacterium
what is the distinctive feature of a protoeukaryote?
genetic information surrounded by endomembrane (rudimentary nucleus)
which organism gave rise to the mitochondrion?
early α-proteobacterium
which organism gave rise to the chloroplast?
early cyanobacterium
what are the four major groups of protozoa?
- alveolates
- euglenoids
- oomycetes
- sarcodina
what are alveolates?
protozoa that possess alveoli (sac-like membrane structures filled with fluid that lie beneath the cell membrane
what are the main phyla of alveolates?
i. ciliates
ii. sporozoans
iii. dinoflagellates
what are euglenoids?
flagellated protozoa
give some examples of euglenoids
i. Euglena
ii. Trypanosomes
iii. Leishmania
what are oomycetes?
- ‘water moulds’
- filamentous protozoa
- either free-living or parasitic
- may grow as ‘fungal-like’ hyphae
give some examples of oomycetes
i. Phythophthora infestans
ii. Plasmopara viticola
iii. Saprolegnia species
what are sarcodina?
- largest phylum of protozoa
- most are free-living
describe the main features of ciliates
- found almost everywhere there is water
- cell surface covered in cilia that beat to propel the ciliate forwards through water and/or draw in food particles
- free-living ciliates feed mainly on bacteria,algae and other ciliates (Didinium)
- some ciliates harbour symbiotic algae
give examples of ciliates
Paramecium - feeds mainly on bacteria; reproduces asexually or sexually by conjugation
also Vorticella, Stentor
describe the main features of sporozoans
- haploid parasitic protozoa
- complex lifestyle involving growth stage within host cell
- major sub-group is apicomplexans
what are apicomplexans?
distinctive structure at apical end of sporozoite ( involved in host cell invasion)
eg. Plasmodium, Toxoplasma, Elmeria
to which group to cilia and sporozoans belong?
alveolates
describe the main features of Euglena
- many possess chloroplasts
- but also capable of heterotrophic growth
- in some species, chloroplast is easily lost (‘bleaching’)
describe the main features of Tryposomes
- flagellated pathogens of animals and plants
- life cycle involving an insect host
- possess a kinetoplast
eg. Tryposomona brucei - sleeping sickness
what is a kinetoplast?
a specialised DNA-containing structure in mitochondrion
give examples of oomycetes
- Phytophthora infestans - causes potato/tomato blight
- Plasmopare vitizola - causes grape mildew
- Saprolegnia species - grow on the scales of fish; cause lesions when fish are in high density
give an example of a sarcodina
Dictystelium discoideum (Dicty)
describe the main features of Dictystelium discoideum
- haploid unicellular amoeba
- feeds on bacteria in soil
- divides by mitosis (or has a sexual life cycle involving mating types)
- when food becomes scarce, cells undergo a developmental change to create a multicellular organism (‘slug’)
- cells secrete cAMP to attract other cells, which adhere via glycoproteins on the cell surface
- slug differentiates into a fruiting body, which releases spores when mature
- some Dicty display ‘husbandry’; they store cells of bacterial prey as symbionts to take with them to their new niche
how long is a slug?
2-4 mm
describe the main features of Entamoeba histolytica
- major human pathogen
- two stages in life cycle: 1) motile amoba (trophozoite); 2) cyst
- ingested cysts are resistant to stomach acid and hatch to form amoebae in the colon
- new cysts form and pass through the bowel
- normally no symptoms
- but some individual amoebae become invasive and attack organs, resulting in localised infection (amoebic dysentry) or systemic infection of many organs, including the brain
describe the main features of Entamoeba gingivalis
- related to Entamoeba histolytica
- lives between teeth and is associated with periodontal disease and gingivitis
- doesn’t form cysts
- infects only the mouth
- passed on by kissing
what was the result of selective pressures on the symbiont genome?
- the free-living cyanobacterial ancestor had several thousand genes
- genes no longer required for endosymbiotic existence (eg. genes for flagella, cell wall, scavenging micronutrients) were quickly lost
- genes for metabolic pathways duplicated by the host were lost
- many genes were transferred from the cyanobacterium to the host nucleus
- modern-day chloroplast contain a circular genome of 100-200 genes
- roughly a 90-95% reduction in size and complexity compared to cyanobacterial genome
what was the result of primary endosymbiosis?
Chlorophyla = green algae (chlorophyll a, chlorophyll b) Rhodophyta = red algae (chlorophyll a, phytobilins) Glaucocystophyla = glaucos (chlorophyll a, phytobilins)
explain why the study of volvox is so useful
- simple model system for investigating multicellularity and cell differentiation
- two cell types: a) small, flagellated somatic cells around the surface of the sphere; b) large germ-line cells embedded within the matrix of the sphere
describe the main features of glaucocystophytes
- relatively insignificant group of freshwater algae
- only ~13 species described
- interesting from an evolutionary perspective, since chloroplast has retained peptidoglycan cell wall of the original gram-negative cyanobacterium
what are the stages of secondary endosymbiosis?
- capture of a photosynthetic eukaryote
- establishment of a symbiont
- symbiont reduced to an organelle
- nucleomorph lost
what do Chlorarachniophytes and Cryptophytes have in common?
- arose by separate endosymbiotic events involving a green and red alga, respectively
- but they share the common feature of a nucleomorph
what is so remarkable about Chlorarachniophytes and Cryptophytes?
- cells possess four genomes, each with a different evolutionary history:
- nuclear genome (eukaryotic host)
- nucleomorph genoms (eukaryotic alga)
- chloroplast genome (cyanobacterium)
- mitochondrial genome (α-proteobacterium) - despite having different origins (red and green algae), the nucleomorph genomes show striking convergent evolution:
- each has become miniaturised to form tiny chromosomes
- with a few thousand tightly-packed genes
- very little intergenomic space
- ‘bonsai chromsomes’
how did Euglena obtain its chloroplast?
in a separate ‘green alga’ endosymbiosis, in which the protozoan host was closely related to modern-day tryposomes
how did the remaining algal groups obtain their chloroplasts?
- by secondary endosymbiosis involving red algae
- heterokonts (including diatoms and brown algae)
- haptophytes (eg. Emiliana)
- (probably) apicomplexa
describe the main features of dinoflagellates
- probably began with a chloroplast from a red alga
- ~50% of species have discarded their chloroplasts (returned to being heterotrophs)
- others replaced this with one from a green alga or a haptophyte(tertiary symbiosis)
- others have temporary chloroplasts (kleptoplastids) obtained from their algal prey and maintained for a few months, without replication
eg. sea slugs
