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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. 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
Yeasts
Algae
Protozoa
Fungi
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
Some
None
Embryo
None
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.
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.
Mycelium.swf
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.
(1)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 direction 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.
Sporangiospores
rhizoid
T2010.gif
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
Location of
fungus
spores
Chlamydospore External
Arthrospore
External
Conidiospore
External
Sporangiospore
Internal
Examples
Mucor racemosus
Geotrichum
candidum
Aspergillus niger
Penicillium notatum
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:
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).
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.
oogonium
Oospores
formation
antheridium
oospheres
oospores
Zygospores
Zygospores are
large, thick-walled
spores formed when
the tips of two
sexually compatible
hyphae of certain
fungi fuse together.
Zygospores
Ascospores
Ascospores are single-celled ,they 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
Basidiospores are single-celled spores, they are
borne on a club-shaped structure called basidium.
Basidiospores
4.3 Major group and properties of fungi
Fungi
hyphae
representives
Sexual spore
Zygomycetes
Non -septate Mucor;
Rhizopus
Zygospore
Ascomycetes
Septate
Neurospora;
Saccharomyces
Ascospore
Basidiomyctes
Septate
Basidiospore
Deuteromycetes
Septate
Agaricus;
amanita
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. 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
T2015.gif
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 dikaryotic state); the latter is the beginnings 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 microorganisms 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 organisms 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 capable 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 microscopic 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 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, 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 flagellated 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.
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 organic molecules.

Seasonal changes in nutrients, light, and
temperature cause fluctuations in algal populations; 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?