Eukaryotic microbes Flashcards
What groups of organisms are in the Opisthokonta?
Fungi and mammals.
What are some of the eukaryotic innovations?
Macronucleus with micronuclei behind
Cell anus
Contractile vacuoles
Cilia
Food vacuoles
Oral groove on surface, sort of like a mouth
What niches do free living single cell eukaryotes occupy?
Every conceivable ecological niche.
Marine trenches Rainforests Artesian and thermal springs Salt lakes Ice floes and glaciers
Nutrition of single celled eukaryotes?
Aerobic and respire - mitochondria, mitosome and hydrogenosomes.
Some are photosynthetic.
Many are hetero-trophic (feed on others) and absorb extra-cellularly digested food.
Some are predatory (amoebas).
A number are parasitic.
Photosynthesis in eukaryotes?
Quite a widely distributed trait.
What are the variations of respiration in eukaryotes?
- Relic Mitochondria
Some parasitic species contain relic mitochondria, mitochondrial-like proteins that cluster together within the cell, surrounded by small double membrane sacs.
Mitosomes of Giardia and Entamoeba lack a genome, lost most mitochondrial functions, and only known function is the synthesis of iron-sulphur clusters.
Genomic sequence data shows that many amitochondriate eukaryotes contain nuclear genes that originated from bacteria – the presence of hydrogenosomes, mitosomes and mitochondrial-like genes in the nucleus suggest mitochondrial loss rather than a pre-mitochondrial state.
- Aerobic respiration not including mitochondria
Parasites which live in the blood, e.g. Trypanosoma brucei
Glycosome of kinetoplastidae contains glycolytic enzymes and may have evolved from the peroxisome, which: lacks a genome of its own; bounded by a single membrane; less than 250/cell; contains the first nine enzymes of glucose and glycerol metabolism.
Locomotion in eukaryotic microbes?
- Pseudopods
These false feet are projections of the plasma membrane. These extend and contract by the reversible assembly of actin subunits into microfilaments. - Flagella
Used for rapid movement. Flagella organelles associated with their own metabolism. Flagella also respond to/initiate signal-transduction cascades. Different to bacterial flagellum. - Cilia
Hair like structures which occur in large numbers on cell surface. Around 0.25µm diameter and 2-20µm long. Move like oars with alternating power and recovery strokes, generating force perpendicular to the cilia’s axis. Synchronised beats. Faster than flagellates. - Gliding locomotion:
Apicomplexan parasites includes several significant pathogens. Use a unique form of actin-based gliding motility to target and invade hosts. Uses highly dynamic actin filaments.
What are the eukaryotic microorganisms?
Protozoa
Diatoms
Fungus
Reproduction in eukaryotic microbes?
- Asexual – Binary Fission
Divides into two approximately equal parts where cytoplasmic division follows mitosis. Flagellates normally divide in a longitudinal plane. The ciliates normally divide in an equatorial or transverse plane, maintaining the correct number of cilia. Replication of the cytosome (cell body exclusive of the nucleus) precedes the divison of the cytoplasm. Amoebas have no fixed plane of division but simply divide into two basically equal halves. - Asexual – variations
- Endodyogeny: Each DNA replication cycle is followed by mitosis and budding
- Leukocyte transformation: Sporozoites infect leukocytes, transforms them and divides by exploiting the mitotic and cytokinetic machinery of the host
- Schizogony: Nuclei 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 – conjugation
No increase in numbers – genetic exchange. Micronucleus undergoes meiosis. Bridge of cytoplasm forms and one haploid nucleus is exchanged with the partner (others disintegrate).
Nuclear fusion – diploid restored. Old macronucleus disintegrates. Mitosis of a new micronucleus. One converts to a macronucleus
Impact of parasitic eukaryotic microbe diseases?
- Socio-economic:
Protozoan parasites commonly affect the poorest people
Significant obstacle to economic and political development
Financial - $12B lost per year in Africa to Malaria - Medical:
Common human infections, especially in the developing world
High burden of morbidity and mortality – 854,600 deaths due to Malaria in 2013 - Biological:
Unique organelles and biochemistry
Evolutionary questions
Complex life-cycles and transmission patterns – key to understanding organisms
Diverse host-pathogen interactions, e.g. immunity and physiology
Impact of eukaryotic microbes on livestock?
Eimeria spp.
Almost all vertebrates, particularly young and a particular problem for farmed animals especially poultry.
Causes coccidiosis which is a parasitic disease of the intestinal tract, disease spreads from one animal to another by contact with infected faeces or ingestion of infected tissue.
Features of eukaryotic parasitic disease?
Eukaryotic pathogens can have complex lifestyles - may have sexual and asexual phases.
Capacity to produce resting stages (highly resistant spores)
Large genomes allows for the accommodation of multiple hosts.
Life cycle stages of eukaryotic microbes?
- Trophozoite – the feeding stage of a protozoan parasite
- Merozoite – daughter cell of asexual replication
- Sporozoite – motile, spore-like stage, typically at the infectious stage of the host
Challenges and advantages of faecal oral transmission?
Challenges:
Resisting the environment; high parasite numbers so need high numbers
Need a way of sensing entry into the host
Host availability can be problematic
Advantages:
Adaptation focused on a single host type
Ease of entry into host by ingestion
Can remain metabolically inactive in the environment for survival
Example of a human intestinal parasite?
Cryptosproidiosis
Infects a wide range of animals and can cause very large water borne outbreaks.
Oocysts (cyst containing a zygote) are discharged into water, which after ingestion form Sporozoites which infect intestinal cells, producing more oocysts.
Can cause life-threatening diarrhoea in the immuno-compromised.
Prevention is difficult as the oocyst is highly resistant.
High quality of the water does not preclude disease.
