Freshwater Microorganisms

Freshwater Microorganisms • Amoebas are composed of just one cell. They are protozoans with no fixed shape. • Amoebas move by making part of its body move in the direction it wants to travel (a pseudopod). Then slowly the rest of the cell follows. In order to eat, an Amoeba flows around other microorganisms and then engulfs them. To reproduce the Amoeba splits itself into two cells. • Certain kinds of Amoeba can cause Amoebic Dysentery. Paramecium • This slipper-shaped protozoan is found in lakes, ponds, and puddles. Its constantly moving by beating rows of microscopic hairs, called cilia, that work like miniture oars. Paramecium feeds on bacteria and other microoriganisms by sweeping them into its groove shaped mouth. • It has contractile vacuoles to pump water out to maintain homeostasis. Blepharisma • The Blepharisma is a common ciliate found in most any pond. If it lives in bright sunlit ponds it is usually colorless. When exposed to an intense artificial light, the pink pigment emits a poisonous toxin that completely disintegrates the creature. Euglena • Euglena A genus of unicellular, green, photosynthetic protists, sometimes regarded as algae (division Euglenophyta), sometimes as protozoa (class Phytomastigophora). The cell body is typically spindle- shaped but is capable of broadening and narrowing to some extent; it is motile with a single flagellum. Euglena is common in all fresh-water habitats, especially when these are slightly polluted with organic matter. • Euglena has chloroplasts, so it gets its energy by eating and photosynthesizing. Stentor • Stentor, sometimes called trumpet animalcules are a genus of filter-feeding, heterotrophic ciliate protists, representative of the heterotrichs. They are usually horn-shaped, and reaching lengths of 2 millimeters, they are among the biggest known unicellular organisms. • They are named after Stentor, the Greek announcer. Vorticella • The Vorticella is a protist (protozoan) and belongs to the Phyllum Ciliophora. It is a very interesting, stalked ciliate with an inverted bell shape. The stalk contains a contractile fibril called a myoneme. When stimulated, it shortens, causing the stalk to coil like a spring. • Vorticella usually anchor themselves to small particles of material however, it is not uncommon to see them free swimming. When they undergo fission, they split along the longitudinal axis in a process called budding. When they finally split apart, one keeps the myoneme and the other free swims away and grows its own. The main purpose for the cilia at the top is to sweep food down into the gullet. Didinium Didinium’s main prey, Paramecium Didinium • The Didinium belongs to the Phyllum Ciliophora. They are from 80-200 um long. • Didinium are fast moving carnivorous protozoans that feed almost exclusively on live Paramecium. • When its "nose" (shown at top) strikes a Paramecium it latches on with a threadlike trichocyst. Once captured and paralyzed, the didinium devours the Paramecium whole. • The "C"-shaped structure inside the body is a band shaped nucleus and can sometimes be seen with a regular light microscope. • Didinium will encyst when the food source is depleted and excyst when the food returns. Volvox • Volvox is a Chlorophyte, or green alga. It exists as a grand spherical colony. Each little alga within the colony bears two flagella, whip-like hairs. The individual alga are connected to each other by thin strands of cytoplasm that enable the whole colony to swim in a coordinated fashion. The individual alga also have small red eye spots. • The colonies even have what we could call a front and rear end. Or, since Volvox resembles a little planet, a 'north and south pole'. In the northern region the eyespots are more developed. This helps the colony to swim towards the light. This differentiation of cells make Volvox quite unique. It is a colony that comes really close to being a multi-celled organism. • At the end of its life, Volvox bursts open and the small spheres inside it develop into new Volvox. Trypanosoma brucei • Trypanosoma brucei is a parasitic protist species that causes African trypanosomiasis (or sleeping sickness) in humans and nagana in animals in Africa. There are 3 sub-species of T. brucei: T. b. brucei, T. b. gambiense and T. b. rhodesiense. • These obligate parasites have two hosts – the tsetse fly and mammalian host (possibly human). Because of the large difference between these hosts, the trypanosome undergoes complex changes during its life cycle to facilitate its survival in the insect gut and the mammalian bloodstream. Toxoplasma gondii • Toxoplasma gondii is a species of parasitic protozoa in the genus Toxoplasma. The definitive host of T. gondii is the cat, but the parasite can be carried by many warm-blooded animals (birds or mammals). Toxoplasmosis, the disease caused by T. gondii, is usually minor. However, it can have serious or even fatal effects on a fetus whose mother first contracts the disease during pregnancy or on an immunocompromised human or cat. Plasmodium • Plasmodium is a genus of parasitic protists. Infection by these organisms causes malaria. • Of the over 200 known species of Plasmodium, at least 10 species infect humans. Other species infect animals, including monkeys, rodents, birds, and reptiles. The parasite always has two hosts in its life cycle: a mosquito vector and a vertebrate host. Daphnia • Daphnia are tiny crustaceans, never growing larger than a couple of millimeters no matter how well they eat. They are sometimes called water fleas because they are about that size and superficially look like fleas. • But unlike fleas they are nearly transparent, live in water, have a shell, and are graced with an interesting array of modified appendages for sensing, feeding, and swimming. Daphnia are free swimmers, propelling themselves with surprising speed, considering they use a pair of modified antennae to swim. As they travel they filter even tinier organisms from the water. They feed on single-celled algae, yeast, and bacteria. Daphnia in turn are eaten by fish and aquatic insects. It seems that their role in life is to provide a snack for a larger organism. • Eggs are carried in the brood pouch on the back. The heart, found just above the brood patch, can be seen beating in live specimens. .

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