Eukaryotic microogranisms_1

Eukaryotic microogranisms_1

1. DIFFERENCES BETWEEN PROKARYOTIC AND EUKARYOTIC CELLS

   • Eukaryotes more complex - specialised cells
   • Size;
     • Eukaryotes; 2->100um Prokaryotes <2um
   • DNA bound nucleus
     • Eukaryote; Yes Prokaryote: No
   • DNA
     • Eukaryotes; Linear, chromosomes (with histones) Prokaryotes; Single molecule CCC, plasmids
   • Membranes
     • Eukaryotes: Sterols Prokaryotes; No sterols
   • Ribosomes
     • Eukaryotes; 80S (70S in mitochondria) Prokaryotes 70S
       • Cell wall;
         • Eukaryotes; Yes in plants, algae, fungi. No in animals, protozoa Prokaryotes; Mainly present
   • Membrane bound organelles
     • Eukaryote; Yes Prokaryotes; No
   • Motility
     • Eukaryote; Flagella or cilia Prokaryote; Flagella

2. PROTOZOA

   • Single celled, no cell wall (3-2000um)
   • Free-living, found in soil and water
   • No chlorophyll- obtains nutrients by ingestion (phagocytosis) of other organisms (algae, yeasts, bacteria, other protozoa) or from dead decaying organic matter
   • Parasitic protozoa; absorb nutrients from host
   • Pathogenic protozoa; cause malaria, giardiasis, amoebic dysentery
   • Motility by cilia (ciliates; ciliophora), flagella (flagellates; mastigophora), or amoeboid movement used pseudopodia (amoebas; sarcodina), non motile (sporozoan apicomplexa)

3. PATHOGENIC PROTOZOA

   • Entamoeba histolytica (amoeba) - amoeba dysentery, forms cysts in intestine, difficult to treat
   • Trypanosoma gambiense (flagellate) - African sleeping sickness (tsetse fly)
   • Giardia Lamblia (flagellate) - persistent intestinal infection
   • Sporozoans
     • Plasmodium vivax - malaria (spread by mosquitoes)
     • Pneumocystis carinii and Cryptosporidium - severe secondary infections in immunosuppressed individuals (AIDS)

4. FUNGI

   • contain cell walls (glucans, mannans, chitin), produce spores, non-motile
   • aquatic, marine, mainly terrestrial (soil, dead organic matter)
   • some human pathogens
     • Major plant pathogens
   • no chlorophyll, chemoorganotrophs (chemoheterotroph)
     • simple nutritional requirements
       • decompose dead animal and plant matter (basidiomycetes decompose woody material and utilise cellulose or lignin)
   • Can grow at low pH, high temp (62deg)
   • Used in production of cheeses, wine, beer, antibiotics
   • GROWTH (nutritional) differences between fungi and bacteria
     • Fungi grow better at pH 5, - too acidic for most bacteria
     • almost all moulds are aerobic, most yeasts faculative anaerobes, no strict anaerobes
     • fungi -more resistant to osmotic pressure, can grow in high sugar and salt ocncentrations
     • fungi grow on substrates with little moisture content, lower than can support bacteria
     • fungi can metabolise complex carbohydrates (e.g lignin)
     • fungi needs less N for equivalent amount of growth
     • Both absorb nutrients rather than ingest them

5. MOULDS

   • filamentous fungi
   • filaments grow mainly at tip (extension of terminal cell)
   • filament = hypha (pl, hyphae)
   • compact tufts of hyphae, branch and intertwine = mycelium (macroscopic)
   • hyphae contain more than one nucleus, cytoplasmic movement through cross-walls
   • aerial hyphae form asexual spores (conidia) at tips
   • Sexual spores formed through production of gametes, gametangia (specialised hyphae), haploid cells
   • spores resistant to drying, freezing, chemicals
   • spores germinate --> new hyphae, mycelium.
   • Different fungi = different type of sexual spore
     • 1. Ascospores and oospores produced in an ascus (sac)
     • 2. Basidiospores produced on club-shaped structure (basidium)
     • 3. Zygospores produced by fusion of hyphae

6. MUSHROOMS

   • Filamentous basidiomycetes that form large fruiting bodies (edible part)
   • Saprophytes (soil, tree trunks)
   • Basidiospores germinate in favourable (moist) substrates
   • produce extensive mycelium
   • fusion of haploid mycelia --> dikaryotic cell --> fruiting body

7. YEASTS

   • Unicellular fungi (ascomycetes)
   • spherical, oval, cylindrical (larger than bacteria)
   • divide by budding (new cell from outgrowth of old cell)
   • can form filaments (short chains = "pseudohphae")
     • Filamentous form can be pathogenic
       • E.g Candida --> vaginal, oral,lung infections, systemic tissue damage (AIDS); attaches to epithelial cells in yeast form, penetrates tissue in filamentous form
   • Can reproduce sexually; mating: two cells fuse --> zygote, ascospores form within
   • Grow where sugars presents (fruits, flowers)
   • Some symbiotic, others pathogenic
   • saccharomyces crevisiae: important commercial yeast, ferments sugar--> alcohol (anaerobic), --> CO2 + H20 (aerobic)

8. IMPORTANT FUNGAL DISEASES

   • Few human pathogens (mostly moulds and yeasts)
   • Superficial mycoses
     • Dermatophytes (live on or within skin, on mucous membranes) --> athletes foot, lesions of nails, scalp, hair follicles)
   • C.albicans:
     • Opportunist
     • normal inhabitant of skin
     • mucous membranes of mouth, intestine, reproductive tract
     • Flourishes when nourmal microbiota is reduced (antibiotics, chemical imbalance)--> infections of mouth (thrush), skin, vagina (vaginal candidiasis),
       • can invade bloodstream --> systemic infection
   • Deep-seated and systemic mycoses:
     • Spores of pathogenic fungi inhaled (dust, bird faeces) or enter through wounds on feet or hands
     • Deep seated- internal infections
     • Systemic- spreads through blood and other tissues
   • Inhalation --> germination in lungs, respiratory infection (TB-like); Coccidiodes (coccidiodomycosis), Histoplasma (histoplasmosis), Crytococcus (cyrptococcosis), can invade further -->systemic infection (immunisuppressed)
   • Treatment difficult, many therapeutic agents toxic to humans (eukaryotic)

9. SLIME MOULDS

   • Similar to fungi and protozoa
   • Life cycle includes spore formation (fungal-like)
   • Motile (protozoan like)
   • Live on decaying matter (leaves, soil)
   • Use other microorganisms as food (ingest bacteria by phagocytosis)
   • Amoeboid cells live on bacteria and fungi
   • when conditions unfavourable, amoeboid cells aggregate (some cells produce cAMP, others attracted)
   • "slug" (=amoeba and slimy sheath) migrates towards light
     • after few hours, slug differentiates --> fruiting body
       • some cells --> stalk, others --> spore cap, most --> spores
         • Spores released, germinate--> amoeboid cells
   • More closely related to amoeba
   • sexual spores (macrocytes); aggregates of amoeba, two amoeba conjugate to form large single amoeba, phagocytise others, become enclosed in cellulose wall --> macrocyst (dormant), nucleus (diploid), undergoes meiosis --> haploid nuclei -->vegetative amoeba

10. ALGAE

    • contain chlorophyll (in chloroplasts), carry out oxygenic photosynthesis
    • does not include "blue-green" algae (cyanobacteria)
    • diverse sizes; most microscopic, some (seaweeds, kelp) grow to over 30m
    • unicellular or colonial (strands and aggregates)
    • found in water, soil, plants, rocks
    • most green, some have other pigments (xanthophylls) that mask chlorophyll
    • All algae have chlorophyll a, others have additional chlorophylls (b,c,and d)
    • All carry out photosynthesis using H2O as electron donor, produce o2
      • Some use H2 as electron donor, do not yield o2
    • some can be chemoorgantotrophs, use simple sugars or organic acids in dark
    • Diversity in nature of reserve polymer which results from photosynthesis:
      • starch (a-1,4-glucose)
      • paramylon (B-1,2-glucan)
      • laminarin (B-1, 3-glucan)
      • lipids, mannitol
    • diversity in cell wall chemistry, structure
      • cellulose with other polysaccharides (pectin, xylans, mannans, alginic acids, fucinic acids)
      • calcium carbonate --> coral like algae
      • euglenoids (Euglena) have no cell wall
      • silica in diatoms
      • pores (3-5nm) allows passage of water, inorganic ions, gasses, small nutrient molecules
      • no phagocytosis
      • motility by single or up to four flagella
      • many non-motile with motile gametes
    • can survive in acidic (below pH4) environments