Chapter 4 Eukaryotic Microorganisms

Chapter outline

4.1 Eukaryotic cell structure4.2 Fungal growth and reproduction4.3 Major group and properties of fungi4.4 Yeasts4.5 Slime molds4.6 Protozoa4.7 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 structureCytoplasmicmembrane

Ribosomes

Cytoplasm

Mitochondrion

Nuclear membraneNucleus

Nucleolus

Endoplasmicreticulum

Chloroplast

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.

Molds

Mushrooms Fungi

Yeasts

Algae

Protozoa

Eukaryotic Microorganisms

Major differences among fungi, algae and protozoans

FUNGI ALGAE PROTOZOANS

Kingdom Fungi Protista and Plantee Protista

Nutritional type Chemoheterotroph Photoautotroph Chemoheterotroph

Multicellular All, except yeasts Some None

Cellular

arrangement

Unicellular,

filamentous,

fleshy(such as

mushrooms)

Unicellular,

colonial,

filamentous,

tissues

Unicellular

Food acquisition Absorptive Absorptive Absorptive

cytostome

Characteristic

feature

Sexual and

asexual spores

Pigments Motility; some

form cysts

Embryo None Some None

Protozoa are animallike protists exhibiting heterotrophic nutrition and they can be def- ined as usually motile eukaryotic unicellular microorganisms.

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

Fungi contain cell walls and produce spores, most described species form a relatively tight phylogenetic cluster.

the molds

the yeasts

the mushrooms

4.2 Fungal growth and reproduction

Three major groups of fungi are recognized:

The molds are filamentous fungi. They are widespread in nature. Each filament grows mainly at the tip, by extension of the terminal cell .

Molds

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.

Mycelium.swf

(1)nonseptate (2)septate

The morphology Reproduction Classification Typical species

Filamentous fungi

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 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.

Asexual Spores

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.

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rhizoid

Sporangiospores

Chlamydospores are thick-walled cells within the hyphae

Chlamydospores

Arthrospores

Conidiospores

Conidiospores are arranged in chains at the end of a conidiophore

Conidiospores

Name of fungus

Location of spores

Examples

Chlamydospore External Mucor racemosus

Arthrospore External Geotrichum candidum

Conidiospore External Aspergillus niger

Penicillium notatum

Sporangiospore Internal Rhizopus oryzae

Asexual spores of filamentous fungi

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.

Sexual Spores

1. A haploid nucleus of a donor cell (+) penetrates the cytoplasm of a recipient cell (Plasmogamy).

2. The (+) and (-) nuclei fuse to form a diploid zygote nucleus (Karyogamy).

3. By meiosis, the diploid nucleus gives rise to haploid nuclei (sexual spores), some of which may be genetic recombinants (Meiosis).

A fungal sexual spore results from sexual reproduction, consisting of three phases:

Several types of sexual spores

Oospores Zygospores Ascospores Basidiospores

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

antheridium

oospheres

oospores

oogonium

Oospores formation

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

Zygospores

Zygospores

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

Ascospores

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

Basidiospores

Fungi hyphae representives Sexual spore

Zygomycetes Non -septate Mucor; Rhizopus

Zygospore

Ascomycetes Septate Neurospora;

Saccharomyces

Ascospore

Basidiomyctes Septate Agaricus;

amanita

Basidiospore

Deuteromycetes Septate Aspergillus;

Penicillium

Not found

4.3 Major group and properties of fungi

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. 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.

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.

Fungi differ from bacteria in certain environmental requirements and in the following nutritional characteristics:

4. Fungi are capable of growing on substances with a very low moisture content, generally too low to support the growth of bacteria.

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.

6. Fungi are capable of using complex carbohydrates, such as lignin (wood), that most bacteria cannot metabolize.

5. Fungi require somewhat less nitrogen for growth than bacteria.

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.

Saccharomyces: there are about 30 species. S.cerevisiae are used in the fermentation of beer, wine and in baking. Budding and 4 ascospores.

Typical species of yeasts

Schizosaccharomyces: binary fission and 8 ascospores. Some species are used in the fermentation of beer.

Life cycle of yeast

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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.

Mushrooms

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.

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.

4.6 protozoa

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. 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

Amoeba

Parameicium

Plasmodium

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.

4.7 Algae

Cell structure and characteristics of algae

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).

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

Motility and Ecology of Algae

Typical species of algae

Chlorella: green algae, unicellular

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

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?