L.1-G.Biology
Mycology
D.Ebtihal Muiz
Introduction to fungi
The fungi (singular fungus ) are a kingdom of eukaryotic organisms .
The are heterotrophic and digest their food externally , absorbing nutrient
molecules into their cells . Yeasts , molds and mushroom are examples of
fungi . The branch of biology involving the study of fungi is knownas
mycology (Gr. Mykes mushroom + logos = discourse).
Fungi and bacteria are the primary decomposer of organic matter in
most terrestrial ecosystem . Fungi are characterized by a life cycle that
begins with germination from a spore or resting structure , following by a
period of growth as substrate is exploited to produce biomass ..Finally
there is a period of sporulation , where propagules are formed that can be
disseminated from the parent mycelim.
In this lecture we will discuss what fungi are from a cultural,
ecological, phenotypic - and phylogenetic perspective. How can fungi fit
into two Kingdoms? The answer lies in the way we define the term
fungus (plural: fungi). Fungi are eukaryotic, heterotrophic, absorptive
organisms that develop a rather diffuse, branched, tubular body and
reproduce by means of spores. This describes, not a single
phylogenetic line, but rather a way of life shared by organisms of
different evolutionary backgrounds. We recognize chromistan fungi as
well as eumycotan fungi. If you find this strange, consider the ‘algae’ for
a moment -- they also include representatives of two Kingdoms:
eubacterial prokaryotes (the blue-green cyanobacteria), and chromistans
(the rest). Both algae and fungi are defined functionally or ecologically,
rather than phylogenetically.
Their vegetative cells usually have chitinous cell walls (chitin is a
polymer composed of N-actetylglucosamine). Fungi live in their food,
secreting digestive enzymes that break food polymers into monomers and
oligomers that can be absorbed through the fungal cell wall
Study questions:
1. What features distinguish fungi from other groups of organisms?
2. In what ways are fungi typical eukaryotes?
3. Why are fungi important?
For purposes of classification (which is actually a method of information
1
storage and retrieval), related genera are grouped into families, families
are grouped into orders, orders into classes, classes into phyla, and phyla
into Kingdoms. Here is a sample of how an organism is classified in this
hierarchical (boxes within boxes) system. Note that the binomial is in
italics, as it is in most scientific publications, while the names of higherranking taxa (families, orders, etc) are not in italics. If you refer to a
binomial in writing, it should be underlined, to show that it would be
printed in italics.
Kingdom: EUMYCOTA
Phylum: Dikaryomycota
Subphylum: Basidiomycotina
Class: Holobasidiomycctes
Order: Agaricales
Family: Agaricaceae .
Genus: Agaricus
Species: Agaricus brunnescens -- the edible mushroom.
Hawksworth suggested that since there appear to be about 250,000
species of flowering plants in the world, there are probably six times as
many fungi - about 1,500,000 fungi, in fact. Even if this figure is an overestimate and there are only half-a-million fungi, we have still described
only 20% of the total, and a huge task lies before us.
Mycology is the study of fungi
mykes (Gr.) - cap; mushroom
fungus (L:) = sphongos (Gr.) - sponge
Mycology is improperly coined; according to the rules of Greek
mycetology. There are approximately 70,000 described species of fungi,
however, it is estimated that there are over I million species of fungi on
the planet. Some have
criticized this latter figure a being an overestimate, but suffice it to say
that the majority of the world's species of fungi are yet to be named.
Do you realize that you come into to contact with fungi numerous times
on a daily basis? Just a few example include the bread you had with
dinner, the antibiotics you took to rid your body of a bacterial infection,
or simply the multitude of fungal spores you process with every breath.
Unfortunately, most students of biology do not receive sufficient
education on fungi and are grossly unaware of their importance in society
and in the environment. It is my hope that by the end of this class you
2
will have greatly increased your knowledge of fungal biology and
enhanced your appreciation of fungi and their importance to life on earth.
Summary of Fungal Attributes
From our discussion on how fungi are able to carry out their various
activities, the following attributes can be used to characterize those
organisms that we classify as fungi:
A-They are heterotrophs. That is, they cannot manufacture their
own food from simple compounds as plants are able to do. So
they are dependent on other organisms to produce their foods,
e.g., sugars, starches, proteins, fats, etc. Fungi can be further
divided into saprobes, parasites, symbionts, facultative parasites
and facultative saprobes.
B-The food gathering part of a fungus is made up of either
filamentous, hollow, branched tubes called mycelium or are
single cells called yeasts.
C-Structures called spores reproduce the fungus in the form of
mycelium or yeast cells.
D-They have cell walls. This is a characteristic generally
attributed to plants, but unlike plants, most fungal cell walls are
composed of chitin, a carbohydrate, and is the same material
which makes up the exoskeletons of insects. Plant cell walls are
composed of cellulose.
E-Fungi are eukaryotes as are most other organisms with which
you are familiar. However, bacteria differ from fungi in that
they are prokaryotes.
F-Absorption: The process by which fungi "eat". This differs from the
way in which we eat in that a fungus will digest its food before eating it.
Bacteria are the only other group of organisms that eat in this fashion
3
Humans have utilized/interacted with fungi for thousands of
years
A. Religion:
1-Egypt : the god Osiris produced wine as a gift to humans
2-Greece: Dionysus the god of win& (among other things)
3-Rome: Bacchus the god of wine; mushrooms produced by thunderbolts
thrown to earth by Jupiter
4-Guatemaula & Mexico: mushrooms produced by thunderbolts; use of
hallucinogenic mushrooms in rituals
B:History
1-Ergotism in Europe caused by the fungus Clvaiceps purpurea
2-Irish potato famine caused by the “fungus” Phytophthora infestans
C. Economics & Industry:
1-Food industry: commercial cultivation, cheese, tempeh, food spoilage,
mycotoxins
2-Medicine: vitamins, antibiotics
3-Industrial: organic acids
4-Pathogens: animal & plant
D. Major advances in science
1-Neitrospora crassa: discovered by Shearer & Dodge in 1927 initiated
the field of haploid genetics led to development of many modern genetic
theories, Beadle & Tatum: Nobel prize for one gene-one enzyme; other
biochemical pathways
2-discovery of antibiotics
3-theory of symbiosis
Early scientists and mycologists
1-Van Leeuwenhoek - invention of the microscope, 17th century
2-Pier’ Antonio Micheli - “Father” or founder of modern mycology;
Italian botanist, 1729 publication “Nova Plantarum Genera”; included his
studies on fungi
What are fungi?
Eukaryotic, spore-bearing, heterotrophic organisms that produce
extracelluar enzymes
and absorb their nutrition.
4
Phenotypic and ecological characters of fungi:
I) Body plan:
• reduced thallus: unicellular (yeast), filamentous, or both (=dimorphic),
or else amoeboid/plasmodial
• hyphae are the basic cellular unit in filamentous fungi; they may be
septate or coenocytic (aseptate)
• limited tissue differentiation and division of labor;
somatic (rhizomorphs, stroma and sclerotia) & reproductive structures
plectenchyma: all organized fungal tissue, somatic & reproductive
prosenchyma: loosely woven hyphae, parallel in orientation
pseudoparenchyma: closely packed hyphae, more or less isodiametric
2) Nuclear status:
•eukaryotic; uni, bi- or multinucleate (mono or dikaryons); nucleolus
• may be haploid, diploid (less frequent), homo- or heterokaryotic
• mitosis
intranuclear (except for slime molds); nuclear membrane doesn’t
breakdown during mitosis
centric & noncentric
centric in flagellated forms; typical centrioles of eukaryotes; paired,
cylinders of 9 triplets of microtublues
noncentric in nonflagellated forms; possess spindle pole bodies (SPBs)
differ from centrioles in lacking microtubular component
both centrioles & SPBs are associated with nuclear membrane
3) Organelles:
• mitochondria
•endoplasmic reticulum
• dictyosome cisternae (=golgi apparatus)
•vacuoles
•microbodies
• microtubules
typical eukaryote assemblage of organelles + fungal specific ones
(especially association with cell wall synthesis)
4)Cell wall:
Well-defined, major carbohydrates are chitin and B-glucans (cellulose in
some); know the difference between chitin & cellulose
5
fungal specific organelles involved in cell wall growth
• Spitzenkorper; associated with growing hyphal tips in septate fungi
• chitosome microvesicular struc containing and transporting chitin
syntheses to growing cell wall
• vesicles
5) Nutrition:
a-Heterotrophic, absorptive, produce extrace]lular enzymes
b-Saprobes; pathogens; symbionts (parasites — commensals - mutualists)
c-The role fungi play in their immediate environment is often governed
by what extracellular enzymes they can produce
6) Life cycle: simple to complex; wide variety
7) Sexuality:
• sexual and/or asexual reproduction
• mono; or dioecious
•homo— and heterothallic
•mating systems .heterothallic only
bipolar (unifactorial) - compatibility controlled by alleles of a single
factor or locus
tetrapolar (bifactorial) - compatibility controlled by alleles of two factors,
or loci, located on two different chromosomes
secondary homothallic (bifactorial system) - 2 nuclei with compatible
mating types are incorporated into a single spore
asexual reproduction
• arthrospores
•chlamydospores
• conidia
8) Sporocarps microscopic or macroscopic. limited tissue
differientiation
9) Habitat: ubiquitous
6
Characters that separate the Fungi (=the Kingdom Fungi) from
‘fungi”
Kingdom Fungi
Protistan fungi
mitochondria:
cristae flattened
cristae tubular
motile cells:
no motile cells or posterior
flagella
cell walls
motile cells with
anterior or lateral flagella
chitin
cellulose
alpha-aminoadepic
diaminopimelic
acid (AAA)
(DAP)
carbohydrate:
lysine synthesis :
Oomycota
Phyla:
Chytridiomycota
Hyphochytriomycota
Zygomycota
Labyrinthulomyeota
Basidiomycota
Slime molds (Myxomycota,
Ascomycota
Acrasioimycota)
Some advantages and disadvantages of fungi
Fungi are the agents responsible for much of disintegration of organic
matter , and a such they affect us directly by destroying food , fabrics ,
leather and other consumers , good manufactured from raw materials
subject to fungal attack , they cause the majority of known plant diseases
, and many diseases of animals and of man , they are basis of number of
industrial processes involving fermentation , such as the making of bread
, wines and the preparation of cheeses , and are responsible for the
manufacture of number of antibiotic drugs , notably penicillin . Fungi are
both destructive and beneficial to agriculture, they are responsible for
damage to crops by causing plant disease, while on the other they
increase the fertility of the soil by inducing various changes which result
in the release of plant nutrients in a form available to green plants.
7
General characteristics of the Phyla of the Kingdom Fungi
Chvtridiomvcota:
-unicellular to mycelial
-zoospore with single posterior whiplash flagellum; only flagellated true
fungi
Zygomycota:
-generally aseptate mycelium
-production of zygosporangia & zygospores
Basidiomycota:
-septate mycelium, complex dolipore septa
-dikaryotic, haploid mycelium
-production of exospores (basidiospores) on a basidium
-production of complex sporocarps
Ascomycota:
-septate mycelium, simple septa
-monokaryotic, haploid mycelium
-production of endospores (ascospores) in an ascus
-production of complex sporocarps
8