Microbial Diversity: Eukaryotic Microbes}

Algae

• Photosynthetic, eukaryotic organisms.

• Classified in the kingdom Protista.

• Algal cells consist of cytoplasm, a cell wall, a cell membrane, a nucleus, plastids, ribosomes, mitochondria, and Golgi bodies.

• Some algal cells have a pellicle (a thickened cell membrane), a stigma (a light-sensing organelle, also known as an eyespot), and flagella (whip-like appendage for locomotion).

• More plantlike than protozoa but lack true roots, stems, and leaves.

• Range in size from tiny, unicellular, microscopic organisms (e.g., diatoms, dinoflagellates, desmids) to large, multicellular, plantlike seaweeds (e.g., kelp).

• May be arranged in colonies or strands and are found in freshwater and saltwater.

• Produce energy by photosynthesis, using energy from the sun, carbon dioxide, water, and inorganic nutrients from the soil to build cellular material.

• Most algal cell walls contain cellulose, a polysaccharide not found in the cell walls of any other microorganisms.

• Classified as green, golden (or golden brown), brown, or red depending on the types of photosynthetic pigments they possess.

Algae vs. Plants

• Similarities:

  • Eukaryotic

  • Photosynthetic

  • Cells contain chlorophyll

  • Use carbon dioxide as an energy source

  • Store energy in the form of starch

• Differences:

  • Composed of roots, stems, and leaves: Algae - No; Plants - Yes (most, exceptions include bryophytes)

  • Cell walls contain cellulose: Algae - Most (exceptions include diatoms and dinoflagellates; Euglena and Volvox do not have cell walls); Plants - Yes

  • Method of reproduction: Algae - Both asexual and sexual; Plants - Sexual

  • Contain a vascular system to transport internal fluids: Algae - No; Plants - Yes (most, mosses and other bryophytes are avascular)

Diatoms

• Tiny, usually unicellular algae that live in both freshwater and seawater.

• Important members of the phytoplankton.

• Have silicon dioxide in their cell walls.

• Deposits of diatoms are used to make diatomaceous earth, which is used in filtration systems, insulation, and abrasives.

Green Algae Examples

• Desmids: Unicellular algae, some resemble a microscopic banana.

• Spirogyra: Filamentous alga, often producing long green strands in pond water.

• Chlamydomonas: Unicellular, biflagellated alga, containing one chloroplast and a stigma.

• Volvox: Multicellular alga (colonial alga or colony), consisting of as many as 60,000 interconnected, biflagellated cells, arranged to form a hollow sphere.

• Euglena: Possesses features of both algae and protozoa.

  • Contains chloroplasts, is photosynthetic, and stores energy in the form of starch (algae).

  • Presence of a primitive mouth (cytostome) and the absence of a cell wall (protozoa).

  • Possesses a photosensing organelle called a stigma and a single flagellum.

  • Can sense light and swim into the light.

  • Can obtain nutrients by ingesting food through its cytostome.

  • Possesses a pellicle, which serves the same function as a cell wall—protection.

Algae Importance and Impact

• Important source of food, iodine and other minerals, fertilizers, emulsifiers for pudding, and stabilizers for ice cream and salad dressings; also used as a gelling agent for jams and nutrient media for bacterial growth.

• Nearly 50% oil, studying them as a source of biofuels.

• Agar used as a solidifying agent in laboratory culture media is a complex polysaccharide derived from a red marine alga.

• Damage to water systems is frequently caused by algae clogging filters and pipes if many nutrients are present.

• One genus of algae, Prototheca is a very rare cause of human infections causing a disease known as protothecosis.

  • Prototheca lives in soil and can enter wounds, especially those located on the feet.

  • Produces a small subcutaneous lesion that can progress to a crusty, warty-looking lesion.

  • If the organism enters the lymphatic system, it may cause a debilitating, sometimes fatal infection, especially in immunosuppressed individuals.

• Algae in several other genera secrete substances (phycotoxins) that are poisonous to humans, fish, and other animals.

Protozoa

• Eukaryotic organisms classified in the kingdom Protista.

• Most protozoa are unicellular (single-celled), ranging in length from 3 to 2,000 \,\mu m.

• Most of them are free-living organisms, found in soil and water.

• Protozoal cells are more animal-like than plantlike.

• All protozoal cells possess a variety of eukaryotic structures and organelles, including cell membranes, nuclei, endoplasmic reticulum, mitochondria, Golgi bodies, lysosomes, centrioles, and food vacuoles.

• Some protozoa possess pellicles, cytostomes, contractile vacuoles, pseudopodia, cilia, and flagella.

• Protozoa have no chlorophyll and, therefore, cannot make their own food by photosynthesis.

• Some ingest whole algae, yeasts, bacteria, and smaller protozoans as their source of nutrients; others live on dead and decaying organic matter.

• Do not have cell walls, but some possess a pellicle, which serves the same purpose as a cell wall—protection.

• Some ingest food through a primitive mouth or opening, called a cytostome.

• Some contain an organelle called a contractile vacuole, which pumps water out of the cell.

• Vorticella spp. have a contractile stalk containing a primitive muscle fiber called a myoneme.

• A typical protozoan life cycle consists of two stages: the trophozoite stage and the cyst stage.

  • The trophozoite is the motile, feeding, dividing stage in a protozoan’s life cycle.

  • The cyst is the nonmotile, dormant, survival stage.

• Some protozoa are parasites, breaking down and absorbing nutrients from the body of the host in which they live; many are pathogens.

• Other protozoa coexist with the host animal in a type of mutualistic symbiotic relationship—a relationship in which both organisms benefit.

Protozoa Classification

Protozoa Details

• Amoeba move by means of cytoplasmic extensions called pseudopodia (false feet).

  • Ameboid movement: an ameba extends a pseudopodium in the direction it intends to move, and then the rest of the cell slowly flows into it.

  • Phagocytosis: An ameba ingests a food particle (e.g., a yeast or bacterial cell) by surrounding the particle with pseudopodia, which then fuse together.

  • The ingested particle, surrounded by a membrane, is referred to as a food vacuole or phagosome.

  • Digestive enzymes, released from lysosomes, then digest or break down the food into nutrients.

  • Pinocytosis: When fluids are ingested in a similar manner.

  • One medically important ameba is Entamoeba histolytica, which causes amebic dysentery (amebiasis) and extraintestinal amebic abscesses.

• Ciliates move about by means of large numbers of hairlike cilia on their surfaces exhibiting an oarlike motion and are the most complex of all protozoa.

  • A pathogenic ciliate, Balantidium coli, causes dysentery in underdeveloped countries and is the only ciliated protozoan that causes disease in humans; usually transmitted from drinking water contaminated by swine feces.

• Flagellated protozoa or flagellates move by means of whiplike flagella.

  • A basal body (also called a kinetosome or kinetoplast) anchors each flagellum within the cytoplasm, exhibiting a wavelike motion.

  • Some flagellates are pathogenic.

    • Trypanosoma brucei subspecies gambiense, transmitted by the tsetse fly, causes African sleeping sickness in humans.

    • Trypanosoma cruzi causes American trypanosomiasis (Chagas disease).

    • Trichomonas vaginalis causes persistent sexually transmitted infections (trichomoniasis) of the male and female genital tracts.

    • Giardia lamblia (also known as Giardia intestinalis) causes a persistent diarrheal disease.

• Nonmotile protozoa—protozoa lacking pseudopodia, flagella, or cilia—are classified together in a category called sporozoa.

  • The most important sporozoan pathogens are the Plasmodium spp. that cause malaria and are transmitted by female Anopheles mosquitoes, which become infected when they take a blood meal from a person with malaria.

  • Cryptosporidium parvum causes severe diarrheal disease (cryptosporidiosis) in immunosuppressed patients, especially those with acquired immunodeficiency syndrome (AIDS).

  • Other pathogenic sporozoans include Babesia spp. (the cause of babesiosis),

  • Cyclospora cayetanensis (the cause of a diarrheal disease called cyclosporiasis), and Toxoplasma gondii (the cause of toxoplasmosis).

Fungi

• Found almost everywhere on Earth, some living on organic matter in water and soil (saprophytic fungi), and others living on and within animals and plants (parasitic fungi).

• Fungi also live on many unlikely materials, causing deterioration of leather and plastics and spoilage of jams, pickles, and many other foods.

• Beneficial fungi are important in the production of cheeses, beer, wine, and other foods, as well as certain drugs (e.g., the immunosuppressant drug cyclosporine) and antibiotics (e.g., penicillin).

• A diverse group of eukaryotic organisms that include yeasts, moulds, and mushrooms.

• As saprophytes, their main source of food is dead and decaying organic matter (

Here are some of the significant terms from this note:

• Algae: Photosynthetic, eukaryotic organisms classified in the kingdom Protista.

• Protozoa: Eukaryotic organisms classified in the kingdom Protista; more animal-like than plant-like.

• Fungi: A diverse group of eukaryotic organisms including yeasts, molds, and mushrooms, found almost everywhere on Earth.

• Diatoms: Tiny, usually unicellular algae with silicon dioxide in their cell walls, important members of the phytoplankton.

• Green Algae: Includes desmids, spirogyra, chlamydomonas, volvox, and euglena.

• Trophozoite: The motile, feeding, dividing stage in a protozoan’s life cycle.

• Cyst: The nonmotile, dormant, survival stage in a protozoan life cycle.

• Sporozoa: Nonmotile protozoa lacking pseudopodia, flagella, or cilia; includes Plasmodium, Cryptosporidium, Babesia, Cyclospora, and Toxoplasma.

• Pseudopodia: Cytoplasmic extensions used by amebae for movement and phagocytosis.

• Cilia: Hairlike structures used by ciliates for movement.

• Flagella: Whiplike appendages used by flagellates for movement.