Chapter 4 Eukaryotic Microorganisms

Chapter outline 4.1 Eukaryotic cell structure 4.2 Fungal growth and reproduction 4.3 Major group and properties of fungi 4.4 Yeasts 4.5 Slime molds 4.6 Protozoa 4.7 Algae

Concepts Eukaryotes, genetic material is distributed between cells by the highly organized , complex processes called mitosis and meiosis. Eukaryotic cells differ most obviously from prokaryotic cells in having a variety of membranous organells in the cytoplasmic matrix and the majority of their genetic material within membrane-delimited nuclei. Eukaryotes are heterotrophic microorganisms.

4.1 Eukaryotic cell structure Cytoplasmic membrane Ribosomes Cytoplasm Mitochondrion Nuclear membrane Nucleus Nucleolus Endoplasmic reticulum Chloroplast

The eukaryotic cell is more complex The eukaryotic cell is more complex. All eukaryotes contain a membrane-enclosed nucleus. The eukaryotic cell can be enclosed by a cell wall or cell walls may be absent . Organelles are universal among eukaryotic cells while chloroplasts are found only in photosynthetic cells.

Eukaryotic Microorganisms Molds Mushrooms Fungi Yeasts Algae Protozoa

Major differences among fungi, algae and protozoans Kingdom Fungi Protista and Plantee Protista Nutritional type Chemoheterotroph Photoautotroph Multicellular All, except yeasts Some None Cellular arrangement Unicellular, filamentous, fleshy(such as mushrooms) colonial, tissues Unicellular Food acquisition Absorptive cytostome Characteristic feature Sexual and asexual spores Pigments Motility; some form cysts Embryo

Fungi are heterotrophic eukaryotic microorga- nisms Fungi are heterotrophic eukaryotic microorga- nisms. They are nonphotosynthetic and typically form reproductive spores. Algae are phototrophic eukaryotes that contain photosynthetic pigments within a structure called the chloroplast Protozoa are animallike protists exhibiting heterotrophic nutrition and they can be def- ined as usually motile eukaryotic unicellular microorganisms.

4.2 Fungal growth and reproduction Fungi contain cell walls and produce spores, most described species form a relatively tight phylogenetic cluster. Three major groups of fungi are recognized: the molds the yeasts the mushrooms

Molds The molds are filamentous fungi. They are widespread in nature. Each filament grows mainly at the tip, by extension of the terminal cell . A single filament is called a hypha (plural, hyphae). Hyphae usually grow together across a surface and form compact tufts, collectively called a mycelium, which can be seen easily without a microscope

In most cases, the vegetative cell of a fungal hypha contains more than one nucleus, often hundreds of nuclei are present. Even if a hypha has cross-walls, cytoplasmic movement is often not prevented, as there is usually a pore in the center of the septum through which nuclei and cytoplasmic particles can move.

nonseptate (2)septate

Filamentous fungi The morphology Reproduction Classification Typical species

The morphology of filamentous fungi The filamentous fungi consists of two parts: the mycelium and the spores. A typical hypha is a nucleated tube containing cytoplasm. Usually there is extensive cytoplasmic movement within a hypha, generally in a direc-tion toward the hyphal tip, and the older portions of the hypha usually become vacuolated and virtually devoid of cytoplasm. Each hypha is about 5-10 um wide.

Reproduction Asexual spores are formed by the aerial mycelium of one organism. When these spores germinate, they become organisms that are genetically identical to the parent. Sexual spores result from the fusion of nuclei from two opposite mating strains of the same species of fungus. Organisms that grow from sexual spores will have genetic characteristics of both parental strains.

Asexual Spores Asexual spores are produced by an individual fungus through mitosis and subsequent cell division; there is no fusion of the nuclei of cells. Several types of asexual spores are produced by fungi.

Main types of asexual spores Sporangiospores Conidiospores Arthrospores Chlamydospores

Sporangiospores Sporangiospores are formed within a sporangium

Rhizopus (class Zygomycetes): These are common bread molds, which cause much food spoilage. They have nonseptate. It forms rootlike hyphae called rhizoid, as well as stolons. Zygospores are produced when plus and minus strains are both present. rhizoid Sporangiospores

Chlamydospores Chlamydospores are thick-walled cells within the hyphae

Arthrospores

Conidiospores Conidiospores are arranged in chains at the end of a conidiophore

Conidiospores

Asexual spores of filamentous fungi Name of fungus Location of spores Examples Chlamydospore External Mucor racemosus Arthrospore Geotrichum candidum Conidiospore Aspergillus niger Penicillium notatum Sporangiospore Internal Rhizopus oryzae

Sexual Spores Some molds also produce sexual spores, formed as a result of sexual reproduction. The latter occur from the fusion either of unicellular gametes or of specialized hyphae called gametangia. Alternatively, sexual spores can originate from the fusion of two haploid cells to yield a diploid cell, which then undergoes meiosis and mitosis to yield individual spores.

A fungal sexual spore results from sexual reproduction, consisting of three phases: A haploid nucleus of a donor cell (+) penetrates the cytoplasm of a recipient cell (Plasmogamy). The (+) and (-) nuclei fuse to form a diploid zygote nucleus (Karyogamy). By meiosis, the diploid nucleus gives rise to haploid nuclei (sexual spores), some of which may be genetic recombinants (Meiosis).

Several types of sexual spores Oospores Zygospores Ascospores Basidiospores

Oospores formed within a special female structure, the oogonium Oospores formed within a special female structure, the oogonium. Fertilization of eggs, or oospheres, by male gametes in an antheridium give rise to oospores. oogonium antheridium Oospores formation oospheres oospores

Zygospores Zygospores are large, thick-walled spores formed when the tips of two sexually compatible hyphae of certain fungi fuse together.

Zygospores

Various ascocarps formed by different ascomycete fungi. Ascospores Ascospores are single-celled ,they are produced in a sac called an ascus. There are usually 8 as-cospores in each ascus. Various ascocarps formed by different ascomycete fungi. plectocarp pyrenocarp discocarp

Basidiospores are single-celled spores, they are borne on a club-shaped structure called basidium.

4.3 Major group and properties of fungi hyphae representives Sexual spore Zygomycetes Non -septate Mucor; Rhizopus Zygospore Ascomycetes Septate Neurospora; Saccharomyces Ascospore Basidiomyctes Agaricus; amanita Basidiospore Deuteromycetes Aspergillus; Penicillium Not found

Classification of fungi The classification of fungi is based primarily on the characteristics of the sexual spores and fruiting bodies present during the sexual stages of their life cycles. The perfect life cycle of many fungi are yet unknown. They are placed in a special class of Deuteromycetes

Typical species of filamentous fungi Mucor (class Zygomycetes): occur in soil and on fruits, vegetables and starchy foods. Some are used in the manufacture of cheeses. Their mycelium are nonseptate and are white or gray. Zygospores are produced when plus and minus strains are both present. No stolons or rhizoids.

Rhizopus (class Zygomycetes): these are common bread molds, which cause much food spoilage. They have nonseptate. It forms rootlike hyphae called rhizoid, as well as stolons. Zygospores are produced when plus and minus strains are both present.

Neurospora (Class Ascomycetes) : this genus is widely used in the study of genetics and metabolic pathways. Some species are responsible for food spoilage, and some species are used in industrial fermentations. Certain species produce ascospores, conidia is usually oval.

Agaricus (Class Basidiomycetes) : The best known species is A Agaricus (Class Basidiomycetes) : The best known species is A. campestris,the field mushroom and A. bisporus ,the cultivated mushroom. Most of the larger species of Agaricus are edible.

Aspergillus (Class Deuteromycetes): the aspergilli are widespread in nature. Some species are involved in spoilage. They are used in a number of industrial fermentations, including the production of the citric acid and gluconic acid. A.niger. The aspergilli produce septate, branching mycelium. Conidia, the colors are black, brown, and green.

Penicillium (Class Deuteromycetes ): members of them occur widely in nature. Some species cause rot or other spoilage. Some are used in industrial fermentations, and penicillin is produced by P.notatum and P.chrysonegum. Some reproduce sexually by ascospore formation. Penicillia have septate vegetative mycelium.

Fungi differ from bacteria in certain environmental requirements and in the following nutritional characteristics: 1. Fungi usually grow better in an acidic pH (5.0), which is too acidic for the growth of most common bacteria. 2. Most molds are aerobic, so they grow on surfaces rather than throughout a substrate. Yeasts are facultative anaerobes.

3. Most fungi are more resistant to osmotic pressures than bacteria are; most fungi are therefore able to grow in high sugar or salt concentrations. 4. Fungi are capable of growing on substances with a very low moisture content, generally too low to support the growth of bacteria.

5. Fungi require somewhat less nitrogen for growth than bacteria. 6. Fungi are capable of using complex carbohydrates, such as lignin (wood), that most bacteria cannot metabolize.

4.4 yeasts Morphological characteristics Reproduction Characteristics of colony Typical species of yeasts

Morphological characteristics Yeasts are usually unicellular. Yeast cells are larger than most bacteria.1-5um in width and 5-30 um or more in length. They are commonly egg-shaped. Yeasts have no flagella. Asexual reproduction is by budding or binary fission; Sexual reproduction is by forming ascospore.

Typical species of yeasts Saccharomyces: there are about 30 species. S.cerevisiae are used in the fermentation of beer, wine and in baking. Budding and 4 ascospores. Schizosaccharomyces: binary fission and 8 ascospores. Some species are used in the fermentation of beer.

Life cycle of yeast

Mushrooms Mushrooms are filamentous basidiomycetes that form large fruiting bodies. They live as saprophytes in the soil or on the trunks of trees. Mushroom basidospores are dispersed through the air and initiate mycelia growth on favorable, usually moist, substrates.

From here an extensive mycelium forms following the fusion of two haploid mycelia to yield a cell containing two nuclei (a dikaryo- tic state); the latter is the beginn-ings of a fruiting body.

4.5 Slime Molds Slime molds have phenotypic similarity to both fungi and protozoa. Like fungi, slime molds undergo a life cycle and can produce spores. However, like protozoa, slime molds are motile and can move across a solid surface.

From a phylogenetic perspective slime molds are more ancient than fungi and some protozoa, but more derived than flagellated protozoa and their evolutio-nary predecessors.

The slime molds can be divided into two groups, the cellular slime molds and the acellular slime molds. For the cellular slime molds vegetative forms are composed of single amebalike cells. For acellular slime molds vegetative forms are masses of protoplasm of indefinite size and shape called plasmodia.

4.6 protozoa Protozoa are unicellular eukaryotic microorga-nisms that lack cell walls . They are generally colorless and motile. Protozoa are distinguished from prokaryotes by their eukaryotic nature and usually greater size, from algae by their lack of chlorophyll, from yeasts and other fungi by their motility and absence of a cell wall, and from the slime molds by their lack of fruiting-body.

Protozoa obtain food by ingesting other organ-isms or organic particles. Protozoa are found in a variety of freshwater and marine habitats; a large number are parasitic in other animals, including humans, and some are found growing in soil or in aerial habitats, such as on the surface of trees.

Most protozoa reproduce asexually, most often by binary fission Most protozoa reproduce asexually, most often by binary fission. Some protozoa also exhibit sexual reproduction , usually by conjugation.

Cell structure and characteristics of protozoa Protozoa are unicellular nonphotosythetic eukaryotic microorganisms and lack cell walls. Protozoans are mostly aerobic heterotrophs, although many intestinal protozoans are cap-able of anaerobic growth. Some protozoa have one nucleus, but others have two or more nuclei.

Typical species of protozoa Euglena Parameicium Amoeba Plasmodium

4.7 Algae Algae are a large group of eukaryotic organisms that contain chlorophyll and carry out oxygenic photosynthesis. Although most algae are of micr-oscopic size and hence are clearly microorganisms, a number of forms are macroscopic. Algae are either unicellular or colonial, the latter occurring as aggregates of cells.

Cell structure and characteristics of algae

Algae cells are eukaryotic, single cells or multicellular Algae cells are eukaryotic, single cells or multicellular. Algae contain chlorophyll and are photosynthetic. Algae have a wide range of sizes and sha-pes. Some colonies become quite complex and superficially resemble higher plants in structure.

The cell wall is thin and rigid, it is often surrounded by outer matrix, which often becomes pigmented and stratified. There are 5 chlorophylls: a, b, c, d, and e. Chlorophylla is present in all algae. Simple sexual reproduction or asexual reproduction (many algae produce flage-llated spores and/or non motile spores in sporangia).

Motility and Ecology of Algae A number of algae are motile, because of flagella; cilia do not occur in algae.

Typical species of algae Chlorella: green algae, unicellular

Diatoms: golden brown in color Diatoms: golden brown in color. They have two overlapping halves; one is larger another is small.

Spirogyra: green algae, filamentous form Spirogyra: green algae, filamentous form. The walls of the filament are continuous. The chloroplasts of Spirogyra form a spiral within the filaments.

Red algae: exhibit tissue differentiation and should be classified as plants. They contain phycocyanin and phycoerythrin in addition to chlorophyll. The red color is due to the phycoerythrin .

Roles of Algae in Nature Algae are an important part of any aquatic food chain, they fix carbon dioxide into org-anic molecules. Seasonal changes in nutrients, light, and temperature cause fluctuations in algal po-pulations; periodic increases in numbers of algae are called blooms.

REVIEW QUESTIONS: 1.Some fungi can reproduce both sexually and asexually. What are the advantages and disadvantages of each? 2. At present time those fungi that have no sexual reproduction cannot be classified with their sexually reproducing relatives. Why? Do you think this is likely to change in the future?

3. The term mushrooming is a proverbial description for expanding rapidly. Why is this an accurate metaphor? 4. How can algae be distinguished from the photosynthetic bacteria? 5. How do protozoa move? Reproduce?