Chapter 4 Eukaryotic Microorganisms

Molds

Mushrooms Fungi

Yeasts

Algae

Protozoa

Eukaryotic Microorganisms

Major differences among fungi, algae and protozoans

Fungi are heterotrophic eukaryotic microorganisms. 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 defined as usually motile eukaryotic unicellular microorganisms.

The morphology Reproduction Classification Typical species

Fungi

Fungi

1. Filamentous fungi

2. Unicellular fungi

The morphology of filamentous fungi

The filamentous fungi consists of two pats: the mycelium and the spores.

The filamentous fungi develop multicellular branching structures known as hyphae, which are connected filaments of vegetative cells. Integrated masses of hyphae are called a mycelium.

Each hypha is about 5-10 um wide.

(1)nonseptate;

(2)septate

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

Asexual spores

Sporangiospores （孢囊孢子） Conidiospores （分生孢子） Arthrospores or Oidia （节孢子） Chlamydospores （厚壁孢子）

Sporangiospore

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.

Sporangiospore

rhizoid

Chlamydospores are thick-walled cells within the hyphae

Chlamydospores

Arthrospores

Conidiospores

Conidiospores are arranged in chains at the end of a conidiophore

Conidiospores

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

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).

Sexual Spores

The method of a serial dilutions for viable counting

Chlamydospore External Mucor racemosus

arthrospore External Geotrichum candidum

Conidiospore External Aspergillus niger

Penicillium notatum

Sporangiospore Internal Rhizopus oryzae

Asexual spores of filamentous fungi

Name of fungus Location of spores Examples

Several types of sexual spores

Oospores （卵孢子） Zygospores （接合孢子） Ascospores （子囊孢子） Basidiospores （担孢子）

The major classes of fungi

OomycetesZygomycetesAscomycetesBasdiomycetesDeuteromycetes

Fungi hyphae representives Sexual spore

Zygomycetes Non -septate Mucor; Rhizopus Zygospore

Ascomycetes Septate Neurospora;

SaccharomycesAscospore

Basidiomyctes Septate Agaricus;

amanitaBasidiospore

Deuteromycetes Septate Aspergillus;

PenicilliumNot found

Classification and major properties of fungi

Oospores （卵胞子） : these are formed within a special female structure, the oogonium( 藏卵器 ). Fertilization of eggs, or oospheres ( 卵球 ), by male gametes in an antheridium ( 雄器 ) 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

Ascospores ： these single-celled spores are produced in a sac called an ascus. There are usually 8 ascospores in each ascus.

various ascocarps formed by different ascomycete fungi.

plectocarp pyrenocarp discocarp

Ascospores formation: 1. yeast 2. Neurospora

Basidiospores: These single-celled spores are borne on a club-shaped structure called basidium.

Basidiospores

Mushroom

Fungi usually grow better in an acidic pH (5.0), which is too acidic for the growth of most common bacteria.

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.

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

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.

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.

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.

Classification of fungi

The classification of fungi, unlike that of bacteria, is based primarily on the characteristics of the sexual spores and fruiting bodies present during the sexual stages of their life cycles. However, 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 abundantly 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. Two well-known species are N. Crassa and N. Sitophila. Some species are responsible for food spoilage, and some species are used in industrial fermentations. Certain species produce ascospores, conidia is usually oval. Because of the characteristic pink or red color of the conidia , they are often called pink bread molds.

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 important economically because 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. Conidia.

yeasts

Morphological characteristics Reproduction Characteristics of colony Typical species of yeasts

Morphological characteristics

Yeasts are usually unicellular. Yeast cells are larger than most bacteria. 1-5 um 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 and wine and in baking. Budding and 4 ascospores.Schizosaccharomyces: binary fission and 8 ascospores. Some species are used in the fermentation of beer.

Typical species of yeasts

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 shapes. Some colonies become quite complex and superficially resemble higher plants in structure.

The cell wall is thin and rigid. The cell walls of many algae are surrounded by outer matrix, which often becomes pigmented and stratified. Chloroplasts . There are 5 chlorophylls: a, b, c, d, and e. Chlorophyll a is present in all algae. simple sexual reproduction or asexual reproduction (many algae produce flagellated spores and/or non motile spores in sporangia).

Typical species of algae

Chlorella: green algae, unicellularSpirogyra( 水绵 ): green algae, filamentous form. The walls of the filament are continuous. The chloroplasts of Spirogyra form a spiral within the filaments. Diatoms ( 硅藻 ) ： golden brown in color. They have two overlapping halves; one is larger another is small.

Red algae: exhibit tissue differentiation and should be classified as plants. They contain phycocyanin ( 藻蓝蛋白 ) and phycoerythrin ( 藻红蛋白 ) 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 because they fix carbon dioxide into organic molecules that can be consumed by chemoheterotrophs.

Seasonal changes in nutrients, light, and temperature cause fluctuations in algal populations; periodic increases in numbers of algae are called blooms. Blooms of a few species indicate that the water in which they grow is polluted

cell structure and characteristics of protozoa

Protozoa are unicellular nonphotosythetic eukaryotic microorganisms. They generally lack cell walls. There are 65000 species of protozoa. Protozoans are mostly aerobic heterotrophs, although many intestinal protozoans are capable of anaerobic growth. Some protozoa have one nucleus, but others have two or more nuclei.

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

typical species of protozoa

Euglena ( 眼虫 ) ：Amoeba( 变形虫 ):Parameicium( 草履虫 ):Plasmodium ( 疟原虫 ):