Protozoa Study Notes PDF

Phylogeny  Protozoa The name ‘PROTOZOA’ no longer holds a taxonomic status Current use of the name PROTOZOA – Animal-like members of the Kingdom PROTISTA or PROTOCTISTA – It defines a polyphyletic assemblage of primarily single-celled, heterotrophic,...

Phylogeny  Protozoa The name ‘PROTOZOA’ no longer holds a taxonomic status Current use of the name PROTOZOA – Animal-like members of the Kingdom PROTISTA or PROTOCTISTA – It defines a polyphyletic assemblage of primarily single-celled, heterotrophic, eukaryotic organisms – Major feature that sets Protozoans apart from Animals: Each protozoan is an individual cell A single eukaryotic cell represents a functionally complete organism that performs all physiological processes or life functions – Feeding & digestion – Locomotion – Excretion & osmoregulation – Sensory and response behaviours – Reproduction They use their specialised organelles to carry out these life functions Sometimes called ACELLULAR organisms (vs unicellular)  General Characteristics Structural support & protection 1. Cell membrane or plasmalemma – Alone in naked/flexible Amoebas 2. Pellicle – Thickened plasmalemma – Thickening by protein filaments & microtubules & vesciles (alveoli) – Example: Paramecium 3. Test or Lorica (skeleton) – A secreted shell-like covering or material (e.g. sand particles) gathered from environment Cytoplasm in some differentiated into: 1. Ectoplasm = gelatinous 2. Endoplasm = fluid  Locomotion and Feeding structures**: 1. Flagella 2. Cilia 3. Pseudopodia = flowing extensions of cell cytoplasm – **Used to characterize many protozoa taxa Structure of a cilium Flagellum cross section Both show the “9+2” tube of fibrils called an axoneme homologous structures  Nutrition types 1. Autotrophic – rely on photosynthetic but not always 2. Heterotrophic – Saprobic = taking in dissolved organic matter by a) Diffusion b) Active transport c) Pinocytosis – Holozoic = taking in solid foods (organic detritus or prey) by phagocytosis – Symbiotic 1. Parasites: many protozoa e.g. Plasmodium, Trypanosoma 2. Mutualists: some protozoa e.g. Trychonympha in wood-eating insects 3. Commensals: some protozoa e.g. Ciliates in rumen of ungulates – Digestion occurs in membrane-bounded food vacuoles Food vacuole may form on fixed sites = cell mouth = cytostome – E.g. Paramecium Food vacuole may form on any site on cell surface – E.g. Amoeba – Undigested materials discharged: Cytoproct = permanent pores in ciliates Anywhere on cell surface e.g. in Amoeba  Gas Exchange – All use simple diffusion in O2 uptake and CO2 release Excretion & Osmoregulation – Excretion and Osmoregulation are usually intimately associated – Excretion = Elimination of metabolic waste products, esp. excess nitrogen produced as NH3 from deamination of amino acids NH3 is highly soluble but quite toxic Achieved by simple diffusion  Osmoregulation cont… – Regulation of water balance (volume regulation) – Regulation of ionic balance (adjust concentration & proportions of internal ions), Maintenance of osmotic pressure – Balance hypertonic vs hypotonic environments A challenge for freshwater protozoans Achieved by: 1. Active transport 2. Contractile vacuoles = Works with » tubules, » water tracts and » small vesicles Amoeba Paramecium  Sensitivity & response to environmental stimuli – Protozoa show some degree of sensitivity due to: Conductivity of protoplasm Cilia & Flagella are touch-sensitive Extrusomes = membrane bound organelles capable of ejectability Eye spots or stigmata = photo-sensitive Reproduction – Asexual reproduction 1. Binary fission = 2 similar progeny (daughter cells) 2. Multiple fission = >2 similar progeny (nucleus divides repeatedly before cytokinesis 3. Budding = A portion of the parent breaks off & differentiates into a new individual 4. Plasmotomy = in some multinucleate spp, parent simply divides in two w/out any mitotic division Binary fission  Common life stages protozoans Many have cyst stages secreted by trophic or spore stages Cysts/spores have four basic functions: – protect against unfavorable conditions – serve as sites for multiplication – assist in attachment to surfaces such as hosts – aid in transmission stage from host to host  Sexual Reproduction 1. Syngamy = production of n cells that fuse to restore 2n condition A. Isogamy = gametes are similar in size & shape B. Anisogamy = gametes of two distinct types C. Autogamy = re-formation of a genetically new nucleus w/in a single individual D. Conjugation = genetic mixing by the exchange of nuclear material between mates  Higher Classification & Biology of Selected Protozoa Phylum Sarcomastigophora – amoebas & flagellates Use flagella or pseudopodia or both Autotrophic or heterotrophic – Subphylum Mastigophora – the flagellates Unifying feature = possession of ≥1 flagella Considered polyphyletic Class Phytomastigophorea – the photosynthetic flagellates Class Zoomastigophorea – the non-photosynthetic flagellates  Phytomastigophorea – Order Euglenida Commonly found in ponds rich in decaying organic matter Body shape maintained by pellicle Most with 2 flagella of unequal lengths Photosynthetic spp (1/3) store food reserves as starchy paramylon 2/3 of euglenids are heterotrophic Reproduction appears to be exclusively asexual Examples: Euglena, Peranema  Order Dinoflagellida – Biflagellate, free-living or symbiotic in freshwater & marine – Body shape maintained by pellicle with alveolar vesicles Alveoli may be filled with cellulose – 50% of spp are photosynthetic; rest are heterotrophic or both Order Volvocida – Volvox and Chlamydomonas  Zoomastigophora Order Choanoflagellida – Uniflagellate, sessile protozoans that are either solitary or colonial – All free-living – Flagellum encircled by a protoplasmic collar  similar to sponge choanocytes – Viewed as transitional link to sponges or as Metazoan ancestors Link also has DNA support  Order Kinetoplastida – Tryapanosomes & relatives – Body shape maintained by non-alveolate pellicle – Uni- or bi-flagellate – Reproduction asexual (binary fission); no sexual reproduction observed – Trypanosomes Are exclusively parasitic in plants, invertebrates & vertebrates Cell covered by glycoprotein layer that protects against host immune system – Glycoprotein composition changes regularly (coded for by ~1000 different genes) Vertebrate parasites cause several serious diseases: Disease Parasite Host Vector _________________________________________________________ Leishmaniasis Leishmania sp. Humans Phlebotomine sandflies - Kala-azar; skin sores & ulcers Trypanosomiasis Trypanosoma spp. - Nagana T. brucei Ungulates Tsetse-flies - Sleeping sickness T. gambiense Humans Tsetse-flies T. rhodesiensis Humans Tsetse-flies - Chagas’ disease T. cruzi Humans Kissing bugs General life cycle of a trypanosoma Parasitic Mastigophora and their predilection sites and diseases they cause Tissue parasites Leishmania, Leishmaniasis, Kala-azar/black fever Attack the skin, liver, spleen Visceral, cutaneous and mucocuteneous leishmaniasis Intestinal parasites, Giardia lamblia, found in water bodies (contaminated) Symptoms manifest themselves following an incubation period ranging from 3 to 25 days and include: – abdominal cramps, – stomach bloating, – intermittent episodes of diarrhoea, and tiredness. Diagnosis is achieved by laboratory examination of a faecal specimen. Reproductive organs Trichomonas vaginalis four flagellates, forms a trophozoites  Order Diplomonadida – Predominantly symbiotic flagellates = both commensals & parasites in vertebrate digestive tracts – With paired nuclei – Each nucleus associated with a bundle of flagella – Lack mitochondria – Reproduction asexual; sexual form unknown – Example: Giardia lamblia Cosmopolitan symbiont in human digestive tract Causes giardiasis (diarrhhea, dehydration & intestinal pain)  Order Trichomonadida – With ≥4 flagella – Lack mitochondria – Commensal or parasitic symbionts Trichomonas vaginalis – sexually transmitted – Most strains have low pathenogenicity  asymptomatic – Other strains cause severe inflamation (itching & discharge) T. tenax = oral commensal/parasite – Obligate mutualists Trichonympha in digestive tracts of wood-eating termites & roaches  Subphylum Sarcodina – the amoebas Primary means of locomotion = pseudopodia Pseudopodia take several forms: – Lobopodia – typically broad with rounded tips (like fingers) – Filopodia – threadlike & often branch – Reticulopodia – always branch extensively & anastomose  dense pseudopodial networks – Axopodia – pseudopodia stiffened by inner core of microtubules Microtubules run along the pseudopodium length through its centre Superclass Rhizopoda – Use lobopodia or filopodia – common in moist or aquatic habitats – Most are free-living; some endosymbiotic – Life cycle in many involves cysts   trophozoites – Class Lobosea = sarcodines with lobose to filiform pseudopodia Order Amoebida – naked Lobosea e.g. Amoeba, Entamoeba – Amoeba = free-living – Entamoeba coli = cosmopolitan commensal in human intestines – Entamoeba gingivalis = commensal in teeth & gums – Entamoeba histolytica = a serious parasite in humans  amoebic dysenetery Order Arcellida – shelled or testate Lobosea – Arcella = secreted shell – Difflugia = shell constructed from sand grains – Both free-living in freshwater – Class Filosea – rhizopodans with filiform pseudopodia With simple or branching filopodia  Phylum CILIOPHORA – the ciliates Higher classification remains unchanged Typically possess cilia categorized by function & structure – Functional cilia categories: 1. Oral ciliature = associated with cytostome & surrounding area  feeding 2. Somatic ciliature = cilia on general body surface  locomotory – Structural cilia categories: 1. Simple cilia 2. Compound ciliature Cirrus = discrete bundle of cilia in a row tapering toward a tip Membranelle = cilia in several adjacent rows leaning toward each other Undulating membrane = flattened sheet of cilia that move as a unit Paramecium  Cytostome position on cell body varies (has taxonomic significance) – Anteriorly located – Laterally located – Ventrally located Pellicle consists of alveoli – Considered homologous with that of Dinoflagellates & Apicomplexa Water expulsion vesicle fixed in position  Dimorphic nuclei or heterokaryotic – Macronucleus is polyploid & vegetative – Micronucleus is diploid & reproductive Sexual reproduction by conjugation & autogamy Life style – 2/3 are free-living Most are mobile & holozoic e.g. Paramecium Some form temporary attachments Others are permanently sessile (attach to substratum) – 1/3 are symbiotic in or on invertebrates & vertebrates – Some are parasitic (Balantidium coli)  Reproduction in ciliates (Paramecium) 1. Asexual reproduction Paramecium divides by transverse binary fission Both nuclei (macro and Micronuclei) increase in size they pull themselves apart macronucles divides amitotically (random distribution of chromosomes between the two newly formed macronuclei micronucleus divide mitotically (spindle forming sharing of chromosomes done) Cytoplasmic constriction forms around the middle of the organism and separates into 2 daughter paramecium.  2. Sexual Reproduction- Conjugation Two compatible mating conjugants adhere to each other at their oral grooves the pellicle breaks down and a cytoplasmic bridge is formed Respective macronuclei disintegrate each micronucleus divides meiotically resulting into 4 daughter micronuclei Three micronuclei disintegrate and disappear. The surviving micronucleus divides once mitotically to form two identical gametic nuclei. – Exchange of the male gametes takes place across the cytoplasmic bridge to opposite conjugant. – Male and female fuse forming zygotic nucleus.  Conjugation cont.. Conjugants separate and go independently. – Zygotic nucleus divides mitotically forming 8 daughter nuclei – Four transform into macronuclei and other four into micronuclei – Three daughter micronuclei degenerate leaving only one the ex-conjugants undergo binary fission – two macronuclei enter each new cell and micronucleus divides mitotically – further division takes place where the two macronuclei separate one going into separate cell and respective micronucleus dividing. – The result is 8 daughter cells from two separated ex- conjugants with four from each.  Sexual Reproduction 1. Syngamy = production of n cells that fuse to restore 2n condition A. Isogamy = gametes are similar in size & shape B. Anisogamy = gametes of two distinct types C. Autogamy = re-formation of a genetically new nucleus w/in a single individual D. Conjugation = genetic mixing by the exchange of nuclear material between mates Fig. 28-11b-2 MEIOSIS Haploid Diploid micronucleus micronucleus Compatible mates The original Diploid macronucleus micronucleus disintegrates. MICRONUCLEAR FUSION Key (b) Conjugation and reproduction Conjugation Reproduction  Phylum Apicomplexa Higher Classification – Class Gregarinea – Class Coccidia Gregarinea – Parasites of invertebrates, mainly annelids & arthropods – Infect body cavity, intestine or reproductive system of hosts – Most spp produce a resistant spore or oocyst (sporocyst w/ sporozoites) – Hosts typically get infected by ingesting spores – Life cycle usually involves one host & has only 2 phases = sporogony & gamogony – Examples: Monocystis lumbrici, Gregarina cuneata & Stylocephalus longicollis Coccidia – Primarily parasites of vertebrates, in eipithelium of digestive tract, liver, kidneys or blood cells – Are intracellular – Life cycle has 3 major phases: merogony, gamogony & sporogony – Example: Plasmodium spp – life cycles involve 2 hosts  All are parasitic No cilia, flagella or pseudopodia Characterized by presence of the apical complex – Considered important for attaching the parasite to &/or facilitating entry into a host cell – Found at anterior end, beneath cell membrane of motile infective stages Present in sporozoites and merozoites stages Cell membrane strengthened into alveolar pellicle With single nucleus  Apicomplexans are parasites of animals, and some cause serious human diseases One end, the apical complex, contains a complex of organelles specialized for penetrating a host Most have sexual and asexual stages that require two or more different host species for completion The apicomplexan Plasmodium is the parasite that causes malaria Plasmodium requires both mosquitoes and humans to complete its life cycle Approximately 2 million people die each year from malaria (mainly children under 5yrs)  Malaria (plasmodium) Malaria is characterized by severe intermittent fever occurring every 48 or 72 hours, depending on the species. The 48 hour fever is called tertian because it occurs every third day - fever on day 1, no fever on day 2, fever on day 3 and so on. The 72 hour fever is called quartan, because it returns on every fourth day. These vary from asymptomatic infections (no apparent illness), to the classic symptoms of malaria (fever, chills, sweating, headaches, muscle pains), to severe complications (cerebral malaria, anemia, kidney failure) that can result in death.  Asexual reproduction by multiple fission = shizogony – Occurs at 2 or 3 positions in the life cycle: 1. Sporogony = a single zygote  many spores or sporozoites 2. Merogony = a single large multinucleated cell = schizont  many small merozoites 3. Gamogony = a gamont  many gametes Sexual reproduction by syngamy – The resulting zygote undergoes sporogony Involves meiotic divisions first followed by repeated mitotic divisions Anopheles Trophozoite Human mosquito Merozoites Gamont Sporozoites MEROGONY Schizont GAMOGONY Gametes Spores SPOROGONY Zygote Plasmodium developmental stages in red blood cells  Prevention of malaria Avoid the parasite – Female anopheles mosquito – Long sleeved clothes – Repellants – Screens on doors and windows – Being indoors after dusk Biological – Sterile males – Viruses that will only attack the mosquitoes Environmental – Remove vegetation near settlements – Remove stagnant water Treatment/prophylaxis – Malaria Tablets or injections when going to malaria areas. (Atovaquone/Proguanil (Malarone), Chloroquine, Doxycycline, Mefloquine, Primaquine, Tafenoquine) Life cycles of P. falciparum, P. malariae, P. ovale and P. vivax differ in details related to frequency of multiple fission, morphology of schizonts & gametocytes