Protozoa
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Chapter 2 Introduction to Protozoa Background Information Domain Eukarya – Membrane bound organelles, including nucleus Many kingdoms, 40+, depending on what classification scheme is used Classification is always changing Protozoa are animal-like protists Primitive – Single celled – Colonial Gave rise to modern day plants and animals Diversity is the rule in every aspect – – – – Feeding / energetics Life cycles Reproduction Physiology / osmoregulation – Locomotion – Morphology Protozoan Diversity Review of the Eukaryotic Cell Protists lack cellular specialization (with few exceptions) Individual organelles carry out all physiological processes Cell membrane – Barrier to the outside environment – Selective passage of molecules – Plays a role in endo / exocytosis Cytoplasm – Ectoplasm – outer, stiff, portion – Endoplasm – inner, fluid, portion Internal membrane system – Consists of endoplasmic reticulum (ER), Golgi bodies, and lysosomes – Compartmentalizes the cell The Cytoskeleton Main types – Microfilaments (made of Actin) – Microtubules Functions – Maintain cell shape – Locomotion – cilia, flagella, and pseudopodia – Cell division – Transport vesicles around cell Cilia Numerous, short projections that beat in an oar-like fashion to produce movement Consists of microtubule core (axoneme) enclosed in cell membrane – Ring of 9 doublets, plus two singlets, centrally located – (9x2)+2 pattern Anchored by a basal body (9x3 pattern) Flagella Far fewer than cilia, but structurally identical Long Undulate in a whiplike fashion to produce movement Both cilia and flagella require ATP to move Pseudopodia Used for locomotion, food capture, and endocytosis Actin disassembly results in a conversion of ectoplasm to endoplasm Protozoan Physiology Same rules apply in single celled organisms as do in metazoans In fact, environmental effects may be more pronounced – Ectothermic – Large SA : Vol Important considerations – – – – Feeding and nutrition Enzyme function Osmoregulation Reproduction Feeding and Nutrition Heterotrophs Photoautotrophs Mixotrophs – Can switch between heterotrophy and autotrophy, depending on conditions Endosymbiotic theory explains how energy producing organelles evolved Nutrition occurs in four phases: – Ingestion – Digestion –mechanical and/or chemical – Absorption – Elimination Digestion typically intracellular. Food is phagocytized and a food vacuole is created. Digestive enzymes are dumped into vacuole Enzyme Function Protein form equals function Enzymes are subject to denaturation under the following conditions: – Extreme pH – Extreme temperature (especially high temperatures) – Extreme salinity. For this reason, osmoregulation is important Osmoregulation Many protists posses a specialized organelle known as a contractile vacuole A collection of tubules known as the spongiome, collect ions from the cytoplasm and deliver them to the contractile vacuole proper The vacuole contracts and its contents are extruded The consequences of being an osmoconformer Reproduction All species reproduce asexually (clonally) – Fission – splitting of parent that results in two or multiple individuals – Budding – portion of parent splits off to form new individual No recombination Budding Hydra (NOT a Protozoan) Though less common some species can even reproduce sexually Conjugation – two individuals fuse – dissolve portions of their cell membranes – exchange genetic material Recombination is the result Asexual vs. Sexual Advantages to clonal reproduction – Allows reproduction in the absence of a mate. Good for isolated species – Allows offspring to be reproduced quickly; no energy is lost to gamete production, fertilization, or development – Perpetuates identical genotypes; beneficial if already well adapted to that environment Disadvantage – Limited genetic possibilities. Constricts the gene pool and species could die out when the environment changes Advantages to sexual reproduction – Increases genetic variability via crossing over, independent assortment of chromosomes, and random fertilization – Result may be better environmental adaptability for certain individuals, and the species as a whole Disadvantage – Finding mates in isolated or sessile species Encystment Water is pumped out and organism forms capsule around itself Benefit is the organism can survive harsh environmental conditions for years – Desiccation resistant – Does not require food – Wind dispersal Chapter 3 - Protozoa Protozoa Name means “first animals” 215,000 described species. Equal to the number of described vascular plants 10 times more diverse than bacteria and viruses Protozoan Ecology Very important ecologically Many are photoautotrophs, and make up 40% of all primary productivity Many make up a large component of plankton communities 25% of the described species live as symbionts. Many of these are parasitic Many are important nutrient cyclers Form and Function Protozoan body was is known as a pellicle Pellicle is composed of the cell membrane and cytoskeleton: – – – – Microfilaments (Actin) Microtubules Vesicles such as alveoli Any combination of the above Phylum Euglenozoa Two main classes – Euglenoidea – Kinetoplastida Both are flagellates Both reproduce asexually Both are solitary Class Euglenoidea 1000 species Elongate Free-living Solitary Reproduction is clonal, and occurs via longitudinal binary fission Posses a contractile vacuole Two flagella, one long, one short Posses a pigmented eyespot that shades the photosensitive paraflagellar body Heterotrophic, photoautotrophic, or mixotrophic Photosynthetic species rotate on their longitudinal access as they swim toward the light Can produce a starch-like carbohydrate – Known as paramylon – Produced in the pyrenoids of their chloroplasts – Stored as granules in cytoplasm Class Kinetoplastida 600 species Reproduce asexually Posses one or two flagella Most are parasitic All posses a conspicuous mass of DNA, known as a kinetoplast, located in one large mitochondrion Link between kinetoplast and parasitic lifestyle of most species – Kinetoplast codes for mitochondrial morphogenesis – Parasites alternate between aerobic and anaerobic host environments Trypanosoma is a gut parasite of insects and blood parasite of vertebrates – Chagas’s disease – African sleeping sickness Tsetse Fly Distribution Trypanosoma possesses one large flagellum that joins an undulating membrane, which runs the length of the organism The pellicle’s protein composition (antigens) is controlled by roughly 1000 genes (40% of the genome) – Thus, the parasite is able to effectively elude the host’s immune system Phylum Chlorophyta Green algae Posses chloroplasts with chlorophyll a and b (same as plants) Can synthesize and store starch Marine and freshwater species Some genera are non-motile and filamentous, such as Spirogyra Others such as Volvox are flagellated, motile, and colonial In Volvox, up to 6000 individual cells may make up a hollow spherical colony Individual cells are connected by cytoplasmic bridges There is some cellular differentiation in Volvox – Non-flagellated gonidia (reproductive cells) can reproduce sexually or asexually During asexual reproduction: – Gonidium undergoes several rounds of fission – Inverted (flagella pointing in) daughter colony is created – Flagella later point out – Daughter colony bursts out of the parent colony Volvox is closely related to plants, but also provides insight to the evolution of animals – Blastocysts look almost identical Phylum Choanoflagellata 600 species Marine and freshwater Tiny - 10µm Solitary or colonial Free-living or sessile Stalked, spherical, or occurring in sheets Not surprising that they are closely related to animals – Closely resemble collar cells of sponges One large flagellum w/ base surrounded by a collar of microvilli Flagellum beats and collar traps bacteria and organic molecules Particles ingested by phagocytosis Intracellular digestion Phylum Retortamonada or Metamonada Often live in anoxic environments – Many living in the guts of insects and vertebrates – Mitochondria typically absent, as a result of this – Thus, adapted for surviving on glycolysis Giardia lamblia posses four flagella Giardia is often contracted by drinking from mountain streams. Symptoms are often referred to as “beaver fever.” (Giardiasis) Phylum Axostylata Another heterotrophic flagellate, closely related to the members of Phylum Retortamonada Trichomonas vaginalis is the most famous representative Small parasite with four flagella that infects the urogenital tract of humans – Can be transmitted sexually Phylum Alveolata Consists of three subphyla: – Dinoflagellata – Ciliophora – Apicomplexa Have similar rDNA sequences Posses alveoli, sacs, deep to the cell membrane Alveolata The most notable shared characteristic is the presence of cortical alveoli, flattened vesicles p acked into a continuous layer supporting the membrane, typically forming a flexible pellicle. In dinoflagellates th ey often form armor plates. Subphylum Dinoflagellata Dinoflagellates 4000 marine and freshwater species Posses chloroplasts – Important 1° producers – Red-brown to gold-brown in color, due to photosynthetic pigments – Chloroplasts acquired through endosymbiosis Contribute to planktonic bioluminescence Some are endoparasites of protozoa, crustaceans, and fish Certain genera responsible for “red tides.” – May result in massive die-offs of shellfish and fish – Harms animals who eat contaminated organisms Posses a sulcus and two flagella Have a skeleton known as a theca (test or lorica) Reproduce via binary fission, or may encyst Subphylum Ciliophora 8000 described ciliates Sophisticated protozoans Have some degree of anterior – posterior polarity Most are motile and solitary Many posses specialized ciliature – Somatic cilia – Oral cilia Function of alveoli is to store Ca2+ Release of Ca2+ causes changes in ciliary beat, and discharge of extrusomes – Trichocysts – long shafts that are thought to defend against predators – Toxicysts – longs shafts with toxin that are used for prey capture – Mucocysts – release mucus and creates sticky surface for prey capture or protective cysts Paramecium changes directions upon colliding with something solid – Known as avoidance reaction – Result of Ca2+ and K+ release from alveoli – Depolarization, similar to an action potential Two very interesting sessile genera, Vorticella and Stentor Vorticella – Colonial – Each cell possesses a long stalk with a spasmoneme (spiral fiber) – Contracts to withdraw from predators Stentor is a similar genus Ciliates have two types of nuclei – Macronucleus – genes are actively transcribed – Micronucleus – master copy of genome; inactive except during cell division. They are diploid with little RNA Shapes and numbers (1 to 20) of these nuclei varies across genera – Bean shaped in Paramecium – String of beads in Stentor Subphylum Apicomplexa or Sporozoa Another group of alveolates The sporozoans, form spores Mostly parasitic Posses an apical complex – Attaches to or penetrates host cell – Cone contains digestive enzymes Four species of Plasmodium that cause malaria – #1 human parasite – 300 million worldwide infected each year – 1% die each year – Anopheles mosquito is the vector Complex life cycle – Sporozoite – motile, infective stage possessing apical complex – Merozoite – motile, reinfective stage, also has apical complex – Gametocytes – reproductive stage. Usually, male and female gametocytes pair up and release gametes (sexual reproduction) – Spore – gametes pair to form zygotes, and a protective capsule is secreted Sporozoites – Injected into blood by mosquito – Attack liver cells Merozoites – Derived from sporozoites – Reinfect liver cells or move to red blood cells (RBCs) – Reinfect RBCs, in pulses Cyclical merozoite release correlates with cyclical nature of malaria symptoms – Chills – Fever – Fatigue due to loss of hemoglobin – Serious damage due to the blocking of capillaries by infected (less pliable) RBCs Gametocytes – Formed in RBCs, but do not pair – Release gametes in the gut lumen of mosquito, after being ingested – Form zygotes which penetrate gut wall and encyst to form spore – Sporozoites, produced in spore, later migrate to salivary glands – Sporozoites released with mosquito’s next blood meal Amoeboid Protozoa Posses pseudopodia for locomotion and prey capture (heterotrophs) Have a complex cytoskeleton Marine, freshwater, and terrestrial species Same design found elsewhere in the animal kingdom – Archeocytes of sponges – Mammalian white blood cells (WBCs) Three main groups of amoeboid protozoans – Amebas – 3 Phyla – Phylum Foraminifera – Phylum Actinopoda Amebas Several important genera that you will study in lab – – – – – Amoeba Chaos Entamoeba Arcella Difflugia May or may not have a test (lorica, theca) Arcella has dome shaped test covering its top; pseudopodia extend from underneath Chaos can reach 5mm in length Diversity of pseudopodia – Lobopodia – wide and rounded – Filopodia – slender and may be branched Freshwater species have one to several contractile vacuoles – No need in marine species Some like Entomoeba histolytica are parasitic – Causes dysentery Phylum Foraminifera The forams Mostly marine Numerous reticulopodia (special filopodia) branch and interconnect to form reticulopodial network Vesicular traffic gives reticulopods a granular appearance Locomotion is accomplished by reticulopodial network – Extends – Anchors to substrate – Retracts Forms a probing net that is also used for finding food Have a test, usually composed of calcium carbonate Most are multichambered. Usually start life occupying one chamber, but extend and secrete new tests May be benthic or planktonic, and there are structural differences between the tests of the two types – Planktonic tests are more fragile – Also have spines to increase surface area, and thus buoyancy Foram tests create natural wonders in the form of chalk and limestone – Pink sands of Bermuda – White Cliffs of Dover in England – Blocks of pyramids Phylum Actinopoda Planktonic Spherical with a perforated test Posses many axopodia – Long, stiff, needle-like pseudopodia – Have microtubule support rods – Can attach and retract – Used for flotation, locomotion, and hunting Distinct cellular regions due to the presence of a layer of pseudopodia (not actinopods) – Cortex – shroud of pseudopodia over the test. Digests prey and transfers nutrients – Medulla – inner portion of cell. Houses nucleus, nutrients, or oil drops for buoyancy Divided into two classes – Radiolaria – Heliozoa Class Radiolaria Marine Mostly planktonic Siliceous, spherical test Large, up to 20cm in some colonial species Class Heliozoa Sun animalcules Marine, freshwater, or terrestrial (on mosses) Contractile vacuoles in freshwater species Similar to radiolarians
