Eukaryotic Microbes PDF

EUKARYOTIC MICROBES  ALGAE: CHARACTERISTICS AND CLASSIFICATION Algae are photosynthetic, eukaryotic organisms. All algal cells consist of cytoplasm, a cell wall (usually), a cell membrane, a nucleus, plastids, ribosomes, mitochondria, and Golgi bodies. ❑ Some have a pe...

EUKARYOTIC MICROBES  ALGAE: CHARACTERISTICS AND CLASSIFICATION Algae are photosynthetic, eukaryotic organisms. All algal cells consist of cytoplasm, a cell wall (usually), a cell membrane, a nucleus, plastids, ribosomes, mitochondria, and Golgi bodies. ❑ Some have a pellicle, a stigma, and/or flagella. Algae range in size from unicellular microorganisms (e.g., diatoms) to large, multicellular organisms (e.g., seaweeds or kelp). Algae produce energy by photosynthesis. ❑ Some may use organic nutrients. ALGAE: CHARACTERISTICS AND CLASSIFICATION Algae may be arranged in colonies or strands and are found in fresh and salt water, in wet soil, and on wet rocks. Most algal cell walls contain cellulose. Depending on their photosynthetic pigments, algae are classified as green, golden, brown, or red algae. Algae include diatoms, dinoflagellates, desmids, Spirogyra, Chlamydomonas, Volvox, and Euglena. Algae are an important source of food, iodine, fertilizers, emulsifiers, and stabilizers and gelling agents for jams and culture media. ALGAE: CHARACTERISTICS AND CLASSIFICATION Diatoms are tiny, usually unicellular algae that live in both freshwater and seawater. Dinoflagellates are microscopic, unicellular, flagellated, often photosynthetic algae. Green algae include desmids, Spirogyra, Chlamydomonas, Volvox, and Euglena, all of which can be found in pond water ALGAE: CHARACTERISTICS AND CLASSIFICATION Desmids are unicellular algae, some of which resemble a microscopic banana Spirogyra is an example of a filamentous alga, often producing long green strands in pond water. Chlamydomonas is a unicellular, biflagellated alga, containing one chloroplast and a stigma. ALGAE: CHARACTERISTICS AND CLASSIFICATION Volvox is a multicellular alga, consisting of as many as 60,000 interconnected, biflagellated cells, arranged to form a hollow sphere. Euglena it possesses features possessed by both algae and protozoa. DIATOMS COMMON POND WATER ALGAE AND PROTOZOA A. Amoeba sp. B. Euglena sp. C. Stentor sp. D. Vorticella sp. E. Volvox sp. F. Paramecium sp. B and E are algae. A, C, D, and F are protozoa. ALGAE IN DIFFERENT ENVIRONMENTS  ALGAE: MEDICAL SIGNIFICANCE One genus of algae, Prototheca, is a very rare cause of human infections (i.e., protothecosis). Algae in several other genera secrete toxic substances called phycotoxins. ❑ Phycotoxins are poisonous to humans, fish, and other animals. ❑ If ingested by humans, the phycotoxins produced by the dinoflagellates that cause “red tides” can lead to a disease called paralytic shellfish poisoning. PROTOTHECA CELLS  PROTOZOA: CHARACTERISTICS Protozoa are nonphotosynthetic, eukaryotic organisms. Most protozoa are unicellular, free- living, and found in soil and water. ❑ Protozoal cells are more animal-like than plant-like. ❑ All protozoal cells possess a variety of eukaryotic structures/organelles. ❑ Protozoa cannot make their own food by photosynthesis; some ingest whole algae, yeasts, bacteria, and smaller protozoa as their source of nutrients.  PROTOZOA: CHARACTERISTICS Protozoa do not have cell walls, but some possess a thickened cell membrane called a “pellicle,” which serves the same purpose—protection. A typical protozoan life cycle has two stages—a trophozoite and a cyst. The trophozoite is the motile, feeding, dividing stage. ❑ The cyst is the nonmotile, dormant, survival stage. Some protozoa are parasites. ❑ Parasitic protozoa cause many human diseases, such as malaria, giardiasis, and trypanosomiasis.  PROTOZOA: CHARACTERISTICS Protozoa are sometimes divided into groups, based on their method of locomotion: ❑ Amoeba move by means of pseudopodia (“false feet”), for example, Entamoeba histolytica, the cause of amebic dysentery. ❑ Ciliates move by means of hairlike cilia, for example, Balantidium coli, the cause of balantidiasis. ❑ Flagellates move by means of whiplike flagella, for example, Giardia intestinalis, the cause of giardiasis. ❑ Sporozoa have no visible means of locomotion, for example, Plasmodium spp., the cause of malaria. A POND WATER AMEBA PROTOZOA THAT CAUSE HUMAN DISEASES Photomicrograph of a Digitally colorized scanning Balantidium coli trophozoite electron micrograph of a (arrows are pointing to the Giardia lamblia trophozoite cilia)  FUNGI: CHARACTERISTICS The study of fungi is called mycology; scientists who study fungi are called mycologists. Fungi are found virtually everywhere. Some fungi are harmful, some are beneficial. Fungi represent a diverse group of eukaryotic organisms that include yeasts, moulds, microsporidia, and fleshy fungi (e.g., mushrooms). Fungi are the “garbage disposers” of nature. Fungi are not plants; they are not photosynthetic.  FUNGI: CHARACTERISTICS Fungal cell walls contain a polysaccharide called chitin. Some fungi are unicellular, while others grow as filaments called hyphae. ❑ Hyphae intertwine to form a mass called a mycelium. Some fungi have septate hyphae (the hyphae are divided into cells by cross walls or septa). Some fungi have aseptate hyphae (the hyphae do not contain septa). Whether or not a fungus has aseptate or septate hyphae is an important clue to its identification.  FUNGI: CHARACTERISTICS Depending on the species, fungal cells can reproduce by budding, hyphal extension, or the formation of spores. There are two general categories of spores: ❑ Sexual spores ❑ Asexual spores (also called conidia) Some fungi produce both asexual and sexual spores. Fungal spores are very resistant structures. FUNGAL COLONIES AND TERMS RELATING TO HYPHAE  FUNGI: CLASSIFICATION Classification of fungi is based primarily on their mode of sexual reproduction and the type of sexual spore they produce. The six phyla of fungi are Zygomycotina, Chytridio-mycotina, Ascomycotina, Basidiomycotina, Microsporidia, and Deuteromycotina. Deuteromycotina or Deuteromycetes include the medically important moulds such as some Aspergillus species and Candida albicans ❑ Fungi in this phylum have no mode of sexual reproduction, or the mode of sexual reproduction is not known. MICROSCOPIC APPEARANCE OF VARIOUS FUNGI ASEXUAL REPRODUCTION IN RHIZOPUS AND ASPERGILLUS MOULDS  FUNGI: YEASTS Yeasts are eukaryotic, unicellular organisms that lack mycelia. Individual yeast cells, also referred to as blastospores or blastoconidia, can be observed only using a microscope. Yeasts usually reproduce by budding, but occasionally by a type of spore formation. A string of elongated buds is known as a pseudohypha (not really a hypha). Some yeasts produce thick-walled, spore-like structures called chlamydospores (or chlamydoconidia). GRAM-STAINED CLINICAL SPECIMEN CONTAINING BUDDING YEAST CELLS  MICROSCOPIC APPEARANCE OF THE YEAST CANDIDA ALBICANS A = Chlamydospores B = Pseudohyphae C = Budding yeast cells (blastospores)  FUNGI: YEASTS Yeasts are found in soil and water and on the skins of many fruits and vegetables. ❑ Yeasts have been used for centuries to make wine and beer. ❑ Saccharomyces cerevisiae is a yeast used in baking. ❑ Candida albicans is the yeast most frequently isolated from human clinical specimens, and is also the fungus most frequently isolated from human clinical specimens.  FUNGI: YEASTS Yeast colonies may be difficult to distinguish from bacterial colonies. ❑ A simple wet mount can be used to differentiate yeast colonies from bacterial colonies. Yeasts are larger than bacteria and are usually oval-shaped. Yeasts are often observed in the process of budding. Bacteria do not bud.  GRAM-STAINED CLINICAL SPECIMEN CONTAINING YEASTS, BACTERIA, AND WHITE BLOOD CELLS COLONIES OF C. ALBICANS ON BLOOD AGAR  FUNGI: MOULDS Often spelled “molds.” Moulds are often seen in water and soil and growing on food. Moulds produce cytoplasmic filaments called hyphae. ❑ Aerial hyphae extend above the surface of whatever the mould is growing on. ❑ Vegetative hyphae grow beneath the surface. Reproduction is by spore formation, either sexually or asexually, on the aerial hyphae (also known as reproductive hyphae).  FUNGI: MOULDS Moulds have great commercial importance. ❑ Some produce antibiotics. Examples: Penicillium and Acremonium ❑ Some moulds are used to produce large quantities of enzymes that are used commercially. ❑ The flavor of cheeses like bleu cheese, Roquefort, Camembert, and Limburger are due to moulds that grow in them.  MICROSPORIDIA A new addition to the Kingdom Eumycota are a diverse group of organisms called microsporidia. Originally thought of as protozoa, recent molecular studies show they share more characteristics with the Eumycota. Microsporidia are about the size of bacteria (1-4 µm) and have a unique organelle called a polar filament. MICROSPORIDIA LIFE CYCLE  FUNGI: FLESHY FUNGI These fungi include mushrooms, toadstools, puffballs, and bracket fungi. They consist of a network of filaments or strands (the mycelium) that grows in soil or on rotting logs. The fruiting body that grows above the ground forms and releases spores. Some mushrooms are edible; some are extremely toxic. FLESHY FUNGI GROWING ON THE FOREST FLOOR FUNGI: MEDICAL SIGNIFICANCE A variety of fungi, including yeasts, moulds, and some fleshy fungi, are of medical, veterinary, and agricultural importance because of the diseases they cause in humans, animals, and plants. The infectious diseases of humans and animals that are caused by moulds are called mycoses. Fungal infections of humans are categorized as superficial, cutaneous, subcutaneous, and systemic mycoses SUPERFICIAL AND CUTANEOUS MYCOSES Superficial mycoses are fungal infections of the outermost areas of the human body—hair, nails, and epidermis. Cutaneous mycoses are fungal infections of the living layer of the skin, the dermis. ❑ A group of moulds collectively referred to as dermatophytes cause tinea (“ringworm”) infections. ❑ Note that “ringworm” infections have nothing to do with worms. ❑ The yeast Candida albicans can also cause cutaneous, oral, and vaginal infections.  SUPERFICIAL AND CUTANEOUS MYCOSES Subcutaneous and systemic mycoses are more severe types of fungal infections. Subcutaneous mycoses are fungal infections of the dermis and underlying tissues (e.g., Madura foot). Systemic mycoses are fungal infections of the internal organs of the body. ❑ Spores of some pathogenic fungi may be inhaled with dust from contaminated soil or dried bird or bat feces. They may also enter through wounds of the hands and feet. A VARIETY OF MOULDS GROWING ON BREAD  DIMORPHIC FUNGI A few fungi, including some pathogens, can live as either yeasts or moulds, depending on growth conditions. This phenomenon is known as dimorphism, and the fungi are called dimorphic fungi. ❑ When grown in vitro at body temperature (37°C), dimorphic fungi grow as yeasts and produce yeast colonies. ❑ When grown in vitro at room temperature (25°C), dimorphic fungi exist as moulds, producing mould colonies. ❑ In vivo, dimorphic fungi exist as yeasts. DIMORPHIC FUNGI LICHENS AND SLIME MOULDS Lichens are observed as colored, often circular patches on tree trunks and rocks. ❑ Lichens are composed of an alga and a filamentous fungus (and sometimes a yeast) living in a mutualistic relationship. ❑ Lichens are classified as protists. Slime moulds are found in soil and on rotting logs. Slime moulds have both fungal and protozoal characteristics. Slime moulds are classified as protists. EXAMPLES OF LICHENS A SLIME MOULD ON THE FOREST FLOOR LIFE CYCLE OF A SLIME MOULD