Lecture on Euglena (PDF)

PHYLUM- PROTOZOA  Kingdom Kingdom Eubacteria Archaea Opalina Myxidium Capable of gliding movement only Nosema Characteristics  Habit & Habitat (solitary/free-living/parasitic)  Cell le...

PHYLUM- PROTOZOA  Kingdom Kingdom Eubacteria Archaea Opalina Myxidium Capable of gliding movement only Nosema Characteristics  Habit & Habitat (solitary/free-living/parasitic)  Cell level- Unicellular  Morphology (external shape & size)  Nucleus (macronucleus/micronucleus)  Locomotor organelles (pseudopodia/flagella/cilia/pelicular contractile structures)  Method of locomotion (amoeboid/flagellar/ciliary/metabolic)  Feeding mode (holophytic/holozoic/pinocytosis/saprozoic/myxotrophic)  Respiration  Reproduction(asexual/sexual)  Special structures  Pathogenic /non-pathogenic  If pathogenic (host, disease/signs & symptoms/life cycle)  Euglena viridis Domain- Eukarya Kingdom- Protista Phylum- Protozoa Subphylum- Sarcomastigophora Superclass- Mastigophora Class- Phytomastigophora Order- Euglenida Genus- Euglena Species- viridis Euglena viridis (eu = true; glene = eye-ball; L., viridis = green) Interesting facts  Considered as connecting link between animals and plants.  A diverse group containing some 54 genera and at least 800 species.  Species of Euglena were among the first protists to be seen under the microscope.  In 1674 the Dutch pioneer of microscopy Antoni van Leeuwenhoek first time observed Euglena.  In low moisture conditions, or when food is scarce, Euglena forms a protective wall around itself and lies dormant as a resting cyst until environmental conditions improve.  Characteristics Habit & Habitats It is a common, solitary and free living freshwater flagellate. found worldwide. Euglena live in fresh and brackish water rich in organic matter and can also be found in moist soils. It is found in freshwater pools, ponds, ditches and slowly running streams. Body structure /Morphology Euglena viridis is elongated and spindle-shaped in appearance. The anterior end is blunt, the middle part is wider, while the posterior end is pointed. From the anterior end arises a whip like flagellum. Euglena are characterized by an elongated cell (60 microns in length) with a single large spherical or oval nucleus, numerous chlorophyll-containing chloroplasts (cell organelles that are the site of photosynthesis), a contractile vacuole (organelle that regulates the cytoplasm), an eyespot/stigma, and one or two flagella. Unlike plant cells, Euglena lack a rigid cellulose wall and have a flexible pellicle (envelope) that allows them to change shape. Sensitivity of Euglena viridis  Euglena viridis have an eyespot/stigma ( works like a sensorial organ) situated in the frontal region.  Eyespot can detect light and is capable of reacting to small changes of the intensity of the light.  Shows photosensitivity and their responses vary according to the intensity of light source.  Normally, it swims parallel to the light rays and towards the source of light.  The stigma (composed by thirty to fifty granules of beta-carotene), together with the thickening on the flagellum, constitutes a sort of ‘optic organelle’ for the animal.  The animal can also respond to various concentrations of chemicals, oxygen and carbon dioxide. This single-celled-organism has a number of organelles to carry out various important bodily functions such as-  Flagellum- A long, mobile filament that the Euglena uses to propel itself in its environment.  Reservoir- The part used for storage of nutrients.  Stigma- A light sensitive-spot that allows the Euglena to detect light, so that it may move towards it in order to conduct photosynthesis.  Chloroplast- The bright green body colour of this organism is due to the presence of chloroplasts inside its cell. Euglena's chloroplasts are quite unique because they are surrounded by three membranes, while those of plants have only two membranes. Organelle that allows the organism to conduct photosynthesis.  Contractile Vacuole- Expels excess water into the reservoir.  Pellicle- Stiff membrane made of proteins and somewhat flexible, can also be used for locomotion when crunching up and down or wriggling.  Nucleus- The central organelle which contains DNA and controls the cell's activity, contained within the Nucleolus. Method of locomotion (flagellar & euglenoid) The structures and pattern of movement of prokaryotic and eukaryotic flagella are different. Eukaryotes have one to many flagella, which move in a characteristic whip like manner. The flagella closely resemble the cilium in structure. The core is a bundle of nine pairs of microtubules surrounding two central pairs of microtubules (called as nine-plus-two arrangement) Each microtubule is composed of the protein tubulin. The coordinated sliding of these microtubules confers movement. The base of the flagellum is anchored to the cell by a basal body.  Stages of flagellar movement Stages of euglenoid movement Long flagellum works as a propeller and helps it to move forward Euglena sometimes shows a very peculiar motion in which waves through water. Flagellum makes a series of lateral movements and as a of contraction pass along the body from anterior to posterior result, a pressure is exerted on water at right angles to its surface. A end and the animal creeps forward. The contractions are series of undulating waves pass along the flagellum from base to tip at brought about by the stretching of protoplasm on the pellicle or the rate of twelve per second that push the animal forward. The flagellar by the localised fibrils, called myonemes, in the ectoplasm. action exerts forces on the surrounding medium that drives the water away from a stationary animal. Feeding mode (Holophytic & Saprozoic)  Holophytic/autotrophic Like green plants it can manufacture its own food by photosynthesis. Food is stored as a specialized complex carbohydrate known as paramylon, which enables the organisms to survive in low-light conditions or helps the organism to survive long periods of light deprivation. Paramylon is most abundantly seen in well-fed individuals.  Saprozoic Euglena normally does not ingest solid food, nutrition. However, in the absence of sunlight euglena lives by this method and feeds on decaying organic substances and absorb food directly through the cell surface via phagocytosis (in which the cell membrane entraps food particles in a vacuole for digestion). Respiration The respiration in Euglena viridis is aerobic. It absorbs dissolved oxygen from the surrounding medium by diffusion. In the process of photosynthesis, during day-time, a good amount of oxygen is liberated. There is every reason to believe that this oxygen is used in metabolic activities. Excretion  Osmoregulation- The water content of the body is regulated by the contractile vacuole which periodically empties into the reservoir. Small accessory vacuoles appear in the cytoplasm and later fuse together to form a large contractile vacuole. On reaching its maximum size it bursts, so as to discharge its contents into the reservoir and hence to the outside.  With the removal of the excess of water some of the dissolved nitrogenous excretory substances also get rid of.  The nitrogenous waste products (ammonia) resulting from catabolism pass out by diffusion through the general surface of the body. Some excretory substance may be emptied by the contractile vacuole into the reservoir.  Euglena ejects its excreta through the cytopharynx and releases them to the surroundings through the cytostome. Near the anterior end is a funnel- like depression, called cell-mouth or cytostome, which leads into a short, tubular cell-gullet or cytopharynx. It is often mistakenly called gullet. Cytopharynx passes into an enlarged, spherical permanent cavity or vesicle in the protoplasm, which is called reservoir. Reproduction(asexual/sexual)  Euglena reproduce asexually through binary fission, a form of cell division.  Euglena reproduce asexually by means of longitudinal cell division, several species produce dormant cysts that can withstand drying.  Reproduction begins with the mitosis of the cell nucleus, followed by the division of the cell itself. Euglena divide longitudinally, beginning at the front end of the cell, with the duplication of flagellar processes, gullet and stigma.  During fission locomotory activities are suspended and the flagellum is withdrawn in some cases. The blepharoplast is the first to divide and the two halves remain attached by a spindle-like structure or by a strand.  Reports of sexual conjugation are rare, and have not been substantiated. Encystment in Euglena viridis  Many protozoans respond to adverse environmental conditions by encysting- they secrete a thick, tough wall around themselves and effectively enter a quiescent state comparable to hibernation.  Euglena viridis encysts during the periods of draught and extreme cold.  During the encystment process, the protozoan cell undergoes a series of changes that considerably reduce the complexity of the organism. The cyst wall is composed of a varying number of layers, the components of which are dependent on the species. Flagellated organisms and ciliates lose their flagella and cilia, the contractile vacuole and food vacuoles disappear, and the distribution of organelles within the cell may be reorganized. In some species the cell volume reduces considerably. These changes are reversed during the process of excystment.  The animal becomes inactive, withdraws flagellum and assumes a round shape.  Gradually, protective walls are secreted.  On the return of favourable condition the cyst wall breaks and the Euglena comes out. Adaptations  The ability to form a resistant cyst is widespread among diverse protistan groups and probably developed early in their evolutionary history. Resting cysts also are easily carried by the wind and form an important means of dispersal for species that live in the soil or are common in ephemeral ponds and pools. In climates with distinct cold seasons, the cyst may be an important phase in the annual life cycle.  The cyst plays an important role in the life cycles of several parasitic protozoans that have a free-living dispersal stage, such as Entamoeba histolytica and Cryptosporidium. The cysts are excreted in the host’s faeces and survive in water or soil. Humans are usually infected through drinking contaminated water or eating raw fruit and vegetables grown where human faeces are used as fertilizer. Human consumption Starting in 2005, Tokyo-based Euglena Company has started marketing Euglena-based food and beverage products, based on their provision of both plant- and animal-based nutrients. The powdered euglena contains minerals, vitamins and docosahexaenoic, an omega-3 acid. The powder is used as ingredient in other foods to make it more healthy While the fitness of euglena for human consumption had long been surmised, Euglena Co. was the first to develop a technique to cultivate and farm the microorganism in large enough quantities to be commercially viable. Euglena Company is also experimenting with the use of Euglena as a potential fuel source. -A 4gnt KO mice is unique model for gastric cancer. This KO mice spontaneously develops differentiated-type gastric cancer. - E. gracilis is widely used as food supplement to promote human health as it contains rich nutrients. - Paramylon is a member of β-glucans and one of the major component of Euglena. - Chronic inflammation play crucial event in carcinogenesis that is intricately linked with the continuum of pre-cancerous cascade (metaplasia, dysplasia) to invasive carcinogenesis. This study was to evaluate the effect of Euglena on gastric cancer. Euglena and paramylon administration has no significant effect on gastric mucosal thickness  Administration of Euglena or paramylon decrease infiltration of inflammatory cells to gastric mucosa PML- Polymorphonuclear leukocytes Infiltration of inflammatory cells initiate the precursor lesion and cascade to differentiate-type gastric cancer Euglena and paramylon decreases replicating cells and angiogenesis Euglena and paramylon alter inflammatory cytokines expression Euglena and paramylon have no effect on IgA production in small intestine Euglena and paramylon administration decreases expression of cytokines -which promotes progression of gastric carcinogenesis -which promotes migration and invasive properties of cells This study reveals that contrary to notion that major effect of Euglena is due to paramylon, the effect of Eugelna were at similar levels or greater as observed with paramylon. This shows that other bioactive components of Euglena such as vitamin C, E and β-carotene could be important for its anti-carcinogenic effect. Study shows effect of Euglena on factors promoting gastric cancer.