Introduction to Microbiology Eukaryote microorganisms: The Protists Dr A. Fleming Lecture Preview: The Protists What you will learn Protists are : 1) Eukaryotes 2. An extremely diverse collection of organisms 3. Mostly unicellular 4. Usually motile 5. Found where there is moisture 6. Can display complex life cycles (> 1 host) 1
Protists: any eukaryote that is not a Fungi, plant or animal! Form a Polyphyletic group not derived from common ancestor Protists are an extremely diverse group of single-celled microorganisms Protists ( Kindom Protista ) have been artificially grouped They lack a common evolutionary heritage: Traditional protist sub-kingdoms included: Protozoa : chemoorganotrophic protists Algae: photosynthetic protists 2
Protozoa were traditionally grouped according to their means of MOTILITY Flagellates (Mastigophora) Ciliates (Infusoria or Ciliaphora) Amoeba (Sarcodina) Non motile (Sporozoa) However, this grouping is not based on evolutionary relationships, and is not used today The terms are used for description only DNA and RNA sequence analysis has yielded a putative evolutionary tree of protists Protist Phylogenetic Tree (in blue) 3
The current phylogenetic tree has divided the Protists into six Super Groups Classification combines molecular genetic, biochemical and morphological data However, protist classification is on-going Protists may represent the oldest eukaryotic cells Protists? 4
General characteristics of the Protists Distribution: Generally free living Grow where there is moisture Terrestrial protists reside in decaying organic matter or soil can form a major component of plankton (in lakes and oceans) They are important for nutrient recycling Protists can live in association with other organisms (symbiotic or parasitic) Nutrition: 1. Photosynthesis Photosynthetic protists are exclusively aerobic (like plants) Most obtain energy from light obtain carbon from the fixation of CO 2 Some use organic carbon 5
2. Holozoic nutrition: -uptake of solid nutrients by phagocytosis Pseudopodia engulf particles Eats Paramecium through a cytostome Feed via tentacles or funnels 3. Saprozoic nutrition: uptake of soluble nutrients by osmotrophy: - endocytosis, - diffusion - facilitated uptake Sugars Amino acids 6
Morphology: Protists vary from microscopic to macroscopic (>200m) -all protists have a high surface to volume ratio -this ensures molecules can diffuse from into the cell Gonyaulax Stentor 200 µm Chondrus crispus, a red algae (seaweeds) Encystment In response to stress many protists can form a CYST Characterised by a cell wall and low metabolic activity Cysts can act as: 1.A survival body during adverse conditions (e.g. Nutrient deprivation, dessication, ph changes) 2. As reproductive bodies 3. To mediate transfer between hosts in parasitic species Excystment is a reversal from the cyst to the vegetative cell 7
Asexual reproduction Under favourable conditions, protists reproduce by binary fission The nucleus undergoes mitosis 2 identical cells are produced Sexual reproduction: Occurs under stress conditions Gamonts are protists that can produce gametes Fusion of gametes = Syngamy 2N Mieosis 1N 1N 1N 1N gametes 8
Protists have diverse nuclei 1.Vesicular nuclei: spherical, 1-10 µm, distinct nucleolus 2.Ovular nuclei: large 10-100 µm, multiple nucleoli 3.Chromosomal nuclei: - 1 chromosome & a single nucleoli 4.Twin nuclei: a large macronucleus and a smaller micronucleus Two Paramecium bursaria In conjugating position Current* Protist classification... Super Group First rank Opisthokonta Archaeplastids Amoebozoa Rhizaria Chromalveolata Excavata Mesomycetozoa Glaucophyta Tubulinea Cercozoa Cryptophyceae Fornicata Choanomonada Rhodophycae Flabellinea Haplosporidia Haptophyta Malawimonas Chloroplastida Stereomyxida Foraminifera Stramenophiles Parabasalia Acanthamoebidae Gromia Alveolata Preaxostyla Entamoebida Radiolaria Jakobida Mastigamoebidae Pelomyxa Heterolobosea Euglenozoa Eumycetozoa 6 Super Groups Protist describes a group of eukaryotes that share some morphological, biochemical, reproductive and ecological characteristics * Adl et al., (2005), J. Eukaryot. Microbiol. 52, 399-451 9
Super Group Excavata Contains the oldest eukaryotes Most have an oral feeding groove (cytostome) A flagella wafts particles into the cytostome Giardia intestinalis : Free-living, cyst forming parasites found in contaminated water Human pathogen, infects intestine, causes Giardiasis (diarrhoea) Lacks mitochondria / several flagella / 2 haploid nuclei Trichonympha campanula Flagellated (several thousand) / large cells (>100 µm) Feeds by phagocytosis using pseudopodia-like protrusions A mutualist lives in the gut of wood-eating termites Secretes cellulase (produces glucose for the termite) Can account for 1/3 body mass of the termite 10
Trichomonas vaginalis Human pathogen Associates with genitourinary tract of males and females Other members of this sub-group (Trichomonads) are symbionts of the digestive, reproductive and respiritory tracts of many animals Another Sub-rank of the Excavata are the Euglenozoa: Common in freshwater 1/3 of euglenids are photoautotrophic Other members ingest or absorb their food Euglena deses is autotrophic and heterotrophic 11
Euglena is the representative genus of the Euglenids A photoautotroph Contains chlorophyl and carotenoids Cell is bound by the plasmalemma The pellicle comprises proteinaceous strips and microtubules Large nucleus and prominent nucleolus The eye spot orientates the cell to light Reproduces asexually by mitosis Several euglenids cause disease in animals - The trypanosomes - Non photosynthetic 12
Super group Amoebozoa Motility and feeding are via pseudopodia Pseudopodia have distinct morphologies Lobodia (round) reticulopodia (mesh) Filopodia (long&narrow) Ameoba proteus Inhabit moist environments Can be free-living, endosymbionts, parasites or commensals 13
Entameoba histolytica - Causes dysentery - acquired from cyst-contaminated water or food -excystation occurs in the intestine -cells penetrate gut epithelia & enter blood stream -migrate to liver/lungs/skin -cysts excreted in faeces The Amoebozoa includes the slime-molds Acellular Slime Molds (Myxogastria) Exist as a plasmodium: a large multinucleated, cytoplasmic mass They have no individual cell membrane Creeps along, phagocytizing decaying plant material Physarum plasmodium Hemitrichia sporangia When stressed the plasmodium develops stalked sporangia, An aggregate of sporangia is called a fruiting body Spore-producing sexual reproductive structures 14
Life-cycle of acellular Slime-Molds (Myxogastria) 3.Stress induced sporangia formation (resistant cellulose walls) 2. Haploids fuse: Zygote grows but only the nuclei divide 1. Haploid amoeboid or flagellated 4.Following meiosis the spores germinate Dictyostelia discoideum is another slime-mold - Exist as individual amoeboid cells (1) - Common in soil, - eat bacteria and yeasts 1. (2) Upon nutrient depletion cells aggregate into a pseudoplasmodium (3) this is a motile, multicellular mass that can form a slug-like structure (individual cells retain their cell membrane) 2. 3. (4) Cells then differentiate into a stalk with a tip (a fruiting body, the sorocarp) 4. -spores form in the tip 15
Life cycle of the cellular slime mold Dictyostelia discoideum 1n 2n Dictyostelia discoideum is a model organism Cell signalling Development Motility Gene transcription profiling over the developmental time course shows: 40% of all the genes in the genome change their expression during development 16
Super Group Rhizaria Include Radiolarians and Foraminiferans Ameoboid with fine pseudopodia (filopodia): Primary role of pseudopodia is for feeding Many have shells or skeletons The primary source of protist fossils The Radiolarians Actinosphaerium eichhornii Planktonic organisms Can have endo- or exo- silica skeletons Axopodia protrude from a central point : axoplast mucous coated Trap bacteria, protists and even small invertebrates Feed by endocytosis 17
Radiolarian silica tests (shells) Another Rhizaria Sub group are the Foraminiferans (forams) Globigerina sp SEMs of tests Range from microscopic to macroscopic; 20µm several cm Filopodia are arranged in a branched network: reticulopodia -used for motility, anchoring, and in capturing food Have perforated, calcium carbonate shells (tests) live in the sand or attach to algae and rocks some are planktonic 18
The White Cliffs of Dover and the Pyramids are made from the shells of Foraminiferans (Globigerina) Super group Chromalveolata Very diverse group Only have 2 things in common: 1. they contain plastids (contain pigments) 2. cellulose-containing cell walls Three sub-groups: 1. Alveolata 2. Stramenopiles 3. Haptophyta 19
Sub group 1. Alveolata Apicocomplexa Dinoflagellata Ciliophora Plasmodium sp. Gymnosporidium sp. Paramecium sp. Apicocomplexa Plasmodium sp. animal parasites Contain the apical complex -allows penetration of host cell Have complex life-cycles, many stages & >1 host Vegetative cell (Merozoite) Motile infectious stage (Sporozoite) Apical complex 20
Life cycle of Plasmodium vivax, the cause of one type of malaria Dinoflagellates protective cellulose plates impregnated with silicates Gonyaulax Typically has 2 flagella: Planktonic : Important source of food for animals in the ocean Some undergo a population explosion and cause toxic red tides 21
use cilia for motility/ feeding Range from 10 to 3,000 µm in size Structurally complex The majority are free-living Ciliata Asexual reproduction Ciliates divide by binary fission Sexual reproduction involves conjugation Paramecium, a ciliate 22
Stentor, a ciliate During conjugation, two paramecia first unite at oral areas Sexual reproduction by conjugation 23
During conjugation, the micronuclei undergo meiosis Cell Fusion Macronucleus degrades Micronucleus meiosis-> 4 haploids 3 of which disintigrate Nuclear mitotic division Nuclear migration Nuclear fusion Cell separation Super group Chromalveolata Contains photosynthetic organisms Diatoms Brown and golden algae Brown seaweeds and kelp One common characteristic: Share a heterokont flagella at some point in life cycle 24
The Diatoms are significant algae in the oceans Diatoms are free-living photosynthetic cells in aquatic and marine environments Significant part of the phytoplankton, photosynthetic organisms suspended in the water Structure Often compared to a hat box Cell wall has two halves (valves) The larger valve acts as a lid that fits over the smaller valve Cyclotella is a diatom the large outer valve contains silica 25
Red algae and brown algae are multicellular Red algae live in warm seawater economically important Produce agar, a gelatin-like product Brown algae Many brown algae live in cold ocean waters Range from filaments to large, multicellular forms that may reach 100 m in length Multicellular forms of green, red, and brown algae are called seaweeds a common term for any large, complex algae Chondrus crispus, a red algae 26
Rockweed, Fucus, a brown algae Super Group Archaeplastida Includes all organisms with a photosynthetic plastid Includes the Chloroplastida (green algae) Not always green Inhabit a variety of environments Oceans, freshwater, on trees, backs of turtles Diverse morphology: Unicellular, filamentous, tubular, membranous and sheetlike Reproduction: Asexual or Sexual Chlamydomonas produces 16 daughter cells still within the parent cell Sexual reproduction: Spirogyra undergoes conjugation, during which cells exchange genetic material 27
Reproduction in Chlamydomonas, a motile green algae Cell anatomy and conjugation in Spirogyra, a filamentous green algae 28
Volvox, a colonial green algae Summary Protists are an extremely diverse group of microorganisms Display numerous forms of reproduction and nutrition The opposite to all other eukaryotic groups which specialize in particular types of reproduction and feeding Extra Reading Prescott, LM et. Al., Microbiology 7 th edition McGraw-Hill, Boston, 2008 Pages 606-627 29