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For educational purposes only; do not review, quote or
abstract:-- Information on
the basics of Mycology & The
Fungi |
Bacteria ►
An
Introduction To
The
Study of Fungi1
Including Some Bacteria and Slime Molds (Contact) CONTENTS
CLICK on
underlined file names and included illustrations to enlarge:
Introduction The following section on Schizomycophyta, Amoebozoa
and Eumycophyta follows the classification that prevailed from the
latter third of the 20th Century until the present. The arrangement of the various subgroups
is based on the presumed evolution of the most primitive to the more
highly advanced organisms with previous names of groups being included in
parentheses. Although further
rearrangements are expected as more biological and biochemical data are
forthcoming the presented design should enable identification of major
orders, families and genera. Emphasis has been placed on morphological and
behavioral characteristics, and a simple diagrammatic style is used for most
of the illustrations. A binocular microscope with a 20X magnification is
advisable for students wishing to view living and preserved specimens. Greater detail on a particular group of
fungi may be found by referring to publications listed in the References or through Internet searches. This is a self-contained database with a minimum of
links outside its limits. Independent
Internet searches are encouraged for greater detail on a particular fungal
group. Background & Overview
The first scientific effort to classify the fungi was
made by Anton De Bary in 1860. He
divided the fungi into four groups: Saprophytes
(nutrients derived from dean organic material), Facultative Parasites
(able to become parasitic but generally saprophytic, Facultative
Saprophytes (able to become saprophytic but generally parasitic, and Parasites
(only able to survive on a living host).
Mycology was originally a branch
of botany, but fungi are evolutionarily more closely related to animals than
to plants albeit this was not widely accepted until the late 20th
Century. There have been many
schemes developed to classify organisms (see Systems
& Kingdoms) and fungi in particular. Two contemporary proposals to classify
fungi are shown in Table 1 & Table
2. Historically, the bacteria and slime molds were also included under the
broad group "Fungi" until they were separated into "Kingdoms"
of their own (Table 1) (Also See Wikipedia). All of these are alike in one
respect: they lack chlorophyll and
thus cannot make their own food.
They, like animals, depend for their food either directly or
indirectly on green plants. The following sections discuss diagnostic structures
that aid in the identification of the major organism groups in an arrangement
that begins with primitive forms and proceeds to the more advanced. Included are Bacteria (Monera, Schizomycophyta), Slime Molds (Amoebozoa), and the True Fungi (Eumycophyta) and their principal Classes: Zygomycota (zygote fungi), Ascomycota
(sac fungi), Basidiomycota (higher fungi),
and Deuteromycota (Fungi Imperfecti). Representative Genera and some species of
major families are included. Of
special interest is that sexual processes that appear throughout these groups
gradually disappear as they ascend the evolutionary ladder. The systematic study of these organisms is
scarcely two hundred years old, but humans have known the manifestations of
this group of organisms for thousands of years. Yet today few realize how intimately our lives are linked with
them. They plan such an important
role in the slow but constant changes taking place around us because of their
ubiquity and their amazingly large numbers.
They are the agents responsible for much of the disintegration of
organic matter, and as such they affect us directly by destroying food and
fiber and other goods that are manufactured from raw materials subject to
their attack. They cause the majority
of plant diseases and man7y diseases of animals and humans. They are the basis of a number of
industrial processes involving fermentation, such as making wines, bread,
beers and even the fermentation of the cacao bean and the preparation of
certain cheese. They are deployed in
the commercial preparation of many organic acids and of some vitamins, and
are responsible for the manufacture of a number of antibiotic drugs, notably
penicillin. Fungi in particular are
both destructive and beneficial to agriculture. On the one hand they do extensive damage to crops by causing
plant disease, while on the other they increase the fertility of the soil by
inducing various changes that eventually result in the release of plant
nutrients in a form available to green plants. Their widespread use as edible food in the form of mushrooms
also should not be overlooked. ============================= The fungi rank
prominently in numbers of species among
organisms. Comparison estimates of
some species as of 2010 are noted as follows: Cyanophyta (Cyanobacteria) = 1,800
species Euglenophyta (Euglenozoa) – Flagellate
protozoa = 350 species Chlorophyta (Green algae) = 3,250
species Protista (Chrysophyta) (Golden algae)=
5,225 species Phacophyta (Protista—Brown algae) =
1,675 species Rhodophyta (Red algae) = 2,810 species Dinoflagellata (Pyrophyta -- fire algae) = 1,215 species Monera (Bacteria) (Shizomycophyta -- = 2,200 species Protista (Myxomycophyta) = 535 species Eumycophyta (Eumycetes) – True fungi =
142,000 species Bryiophyta (Mosses) = 28,000 Tracheophyta (Vascular plants) =
380,000 (most likely many more species exist) The five main food sources that are required by fungi are Carbon, Nitrogen, Minor elements, Vitamins (Thiamin & Biotin) and Oxygen. The main carbon source is Sucrose, but one group, the Mucorales, is unable to use it as a source of carbon. Main Groups of Fungi
Zygomycota (Phycomycetes) -- zygote fungi Ascomycota (Ascomycetes) -- sac fungi Basidiomycota (Basidiomycetes) --
higher fungi Deuteromycota (Deuteromycetes or Fungi Imperfecti) – anamorphic fungi General Characteristics of Fungi The fungi are a group of living
organisms that do not possess chlorophyll.
They resemble green plants as generally they have definite cells
walls, they are usually nonmotile, although they may have motile reproductive
cells, and they reproduce by means of spores. They do not have stems, roots or leaves, nor dor they have a
vascular system as the more advanced types of plants. Fingi are usually
filamentous and multicellular; their nuclei can be seen with relative ease;
their somatic structures with few exceptions show little differentiation and
practically no division of labor. The filaments that make up the
body of a fungus elongate by apical growth (Plate
51). However, most parts of an
organism are capable of growth, and a tiny fragment from almost any port of
the fungus is enough to start a new individual. Reproductive structures are differentiated from somatic
structures and show a variety of forms, which are useful for identification. Few fungi may be identified if their
reproductive stages are not available.
This is becuase with few exceptions the somatic parts of fungi
resemble those of many other fungi. The fungi obtain their food either
by infecting living organisms, by behaving as parasites, or by attacking dead
organic matter. Most fungi, whether
normally parasitic or not, are able to live on dead organic matter, which
makes it possible to grow them on synthetic media. Fungi that live on dead matter are unable to infect living
organisms and are referred to as obligate saprobes. Those capable of inciting disease or of living on dea organic
matter are referred to as facultative parasites or facultative saprobes. Those that require living protoplasm are
obligate parasites. Fungi also differ
from most plants in that they require already elaborated food to live and are
incapable of manufacturing their own.
But, if provided with carbohydrates in some form most fungi can
synthesize their own proteins by utilizing inorganic or organic sources of
nitrogen. Many fungi can synthesize
vitamins, which they need to grow and reproduce as do other organisms. Excess food is usually stored in the form
of glycogen or oil. Fungi vary in their food
requirements. Some are omnivorous and
can live on anything that contains organic matter. Other fungi are more restricted in their diet and a few of the
obligate parasites not only require living protoplasm but are also highly
specializes as to the species and even the variety of host they
parasitize. Enzymes determine what
foods are able to be used. The Fungus Vegetative Body
The mycelium is the entire
vegetative body of a single thalus.
It is composed of thread-like structures or hyphae. The diameter of a hypha varies between 2
and 50 microns. Branching occurs
behind the tip, there being some degree of apical dominance. Walls in the Zygomycota (Phycomycetes) are
principally of cellulose, while in the other
groups the walls may contain a combination of cellulose and fungus chitin.
The mycelial type of thallus is not present in many of the lowest
members of fungi, and a few degenerate forms in the higher fungi also lack
it. Occasionally, as in the Zygomycota, a single hypha will
compose the entire mycelium and cross walls will form at random. The absence of cross walls is known as coenocytic, and is also characteristic of the Zygomycota. Septa are the cross walls and
are characteristic of the higher true fungi (Plate
52b). In some species a pore (hole) is left in the septa and protoplasm is continuous
from cell to cell of the hypha. In the Basidiomycota (Basidiomycetes) a characteristic
feature is that a clamp is formed, and the septa do
not reach to the end of the diameter.
All true fungi (Eumycophyta) have well-defined nuclei. In the coenocytic condition there may be nuclei distributed throughout the hypha (Plate 52a). When mycelia occur in the Phycomycota they are characteristically of the coenocytic type. Septations (cross-walls in the hyphae) are almost entirely lacking.
Vacuoles and food particles and oil droplets also are
distributed throughout the mycelium.
Again in the coenocytic condition nuclei may or may not (usually not)
exhibit conjugate nuclear dividion.
In septate mycelium (with or without septal pores), some species may have many nuclei
distributed in one cell (multinucleate). Other species may have two nuclei per cell
(dicaryotic).
A dicaryotic cell will usually exhibit conjugate nuclear division, which is
the simultaneous division of the two nuclei in a dicaryon. This gives rise to four daughter
nuclei. These generally become
separated by a septum into two cells, the sister nuclei migrating into
different daughter cells.
Also, in the septate condition (septa
= “cross wall”), the two hyphae will fuse (hyphal
anastomosis). This may occur
between hyphae on the same mycelium or on two closely related species. In this condition the nuclei may migrate
over the “bridge.” Further division
may result in daughter nuclei migrating through septal pores to adjoining cells. This results in a heterocaryotic effect, which is where
there are different nuclei in the mycelium.
It allows for a recombination of characters. Most Ascomycota, Basidiomycota and Deuteromycota form mycelia
the hyphae of which are divided by septa.
All hyphae do
not have the same growth rate.
Nevertheless, some forces keep the total margin at an even level
Stolons are parts of hyphae
that skip across the substrate surface.
At points of contact with the substrate, growth is stimulated and
hyphae will penetrate the substrate.
These penetrating hyphae are then called rhizoids.
In some Basidiomycota (Basidiomycetes) a bunch of
horizontal hyphae will form a cable over the
substrate (rhizomorphs). This is typified in Armelaria, the
“shoe-string fungus.” The outer edge of the hyphae forms a thick
cell wall. Its function is believed
to be the transportation of water across dry areas. The cables are usually large enough to be readily viewed
without a microscope and resemble small roots of a seed plant.
Often the fruiting bodies will arise
from rhizomorphs, which is particular true of stinkhorn fungi. Sclerotia (sing. = sclerotium)
is a very dense, heavy-packed group of hyphae surrounded by a thick wall (Plate 56a,b).
They are usually found in the higher fungi, and in certain genera and
species they can be of considerable size.
The outer hyphae are usually thick-walled so that the whole structure
appears firm and hard. The color is
mostly brown or blackish even though the rest of the mycelium may be
white. Sclerotia may store food and
serve as resistant vegetative resting structures when they occur (Plate 56c,d).
Haustoria are usually
found among the obligate parasites where they occur in the intercellular hyphae (= a protuberance
that dissolves the host cell wall and develop into the cell (Plate 53).
There are various kinds and they serve as identification characters
for certain species. Naturally they
do not occur in an intracellular parasite.
Some Eumycophyta are not myceliar and are characterized by a single
cell (e.g., yeasts).
[Please see PLATE 1 and PLATE 2
for additional examples of fungal vegetative bodies.] |
Nature & Reproduction of The Fungi
History
Ancient cultures were well aware of fungi, but they
knew mainly the fleshy kinds. They
did not associate the parasitic forms, such as rusts and mildews, with
disease. They were often amazed at
the rapidity of growth. Theophrastus (3-4 BCE) believed that fungi were
plants without roots, stems and leaves.
The Greeks and Romans formed the spontaneous generation idea of fungus
origins. Pliny (1 AD) proposed that
lightening and thunder were implicated in the rise of fungi. He observed “fairy
rings of fungi,” which are actually the expanding mycelium.
Anton DeBary in 1850
noted that fungi develop from spores.
Franz Unger in 1840 advocated that fungi
were associated with disease and were the results of disease. He believed that the “morbid
sap” of the host was transformed into the fungus. Micheli in Florence, Italy
published Novum Plantarum Genera
in 1729. He described fungi along
with other plants in this book, but he did not believe in spontaneous
generation. He thought that fungi
also had seeds (viewed their powdery spores). In a classic experiment he used two sterile melons, which he
placed under bell jars. He inoculated
one and left the other as a control.
Mycelia developed on the inoculated portion, which he compared with
that of the parent. He repeated the
experiment several times and concluded that because of their lightness,
fungal spores were in the air at all times.
In a second experiment he seeded an area in the leaf mat of a forest
with non-indigenous species of mushroom.
Later he observed mycelium and still later the fruiting bodies. Reproduction in the fungi is varied and sometimes very
complex. A sexual process, or the
equivalent, is often involved.
However the fungi are noted for the diversity of means they possess
for asexual reproduction. ------------------------------------------- Some fungi employ fragmentation of hyphae as a means of
propagation. The hyphae break up into
their component cells, called oidia, which behave
like spores (Plate 57a). If the cells become enveloped in a thick
wall before they separate from each other or from other hyphal cells
adjoining the, they are called chlamydospores
(Plate 57b). Fragmentation may also occur accidentally by the breaking off
of parts of the mycelium through external forces. Such pieces of mycelium under favorable conditions can start a
new individual. Laboratory
propagation is frequently made from mycelial fragments. Fission can occur through the simple
splitting of a cell into two daughter cells by constriction. This is found among the bacteria
generally, but some fungal yeasts may do this also (Plate 58a). Budding is the asexual
production of a small outgrowth from a parent cell. The bud increases in size while still attached to the parent
cell. It eventually breaks off and
forms a new individual (Plate 58b). Sometimes chains of buds form a short
mycelium. Most yeasts have budding,
but it also occurs in many other fungi at different phases of their life
history or under certain conditions of growth. The commonest method of asexual reproduction in fungi
is by means of spores. Spores vary in
color, size, shape, number of cells and the way that the spores themselves
are borne (Plate 58b) ------------------------------------------- Spores are small, detachable
bodies, with either one or more cells and capable of germinating (Plate 54).
Most fiungi produce these small detachable bodies, the function of
which might be compared to that of seeds in higher plants. Although there are many spore types in the
fungi, this discussion will stress basically five different types: Conidia, Sprangiospores, Zoospores
(Planospores), Ascospores and Basidiospores.
Other types include aeciospores, uredospores, pycnospores,
etc. Nevertheless, a number of fungi
form more than one type , e.g., both ascospores and conidiospores), usually
at different stages in their development.
The spores may be either colored or hyaline and exhibit a variety of
shapes. They are frequently
unicellular but may be two- or more celled.
Some fungi bear them on or within a fruiting
body, which consists of a dense aggregation of hyphae. The spore output of some fungi is in the
millions or even billions of spores being produced by a single
individual. They are distributed in a
variety of ways, but when they travel by air currents they can be the source
of severe allergies as they are breathed in and
begin to germinate on the linings of respiratory systems in humans and
animals. During some stages of the life history of most fungi
the mycelium becomes organized into loosely or compactly woven tissues as distinguished
from the loose hyphae ordinarily making up the thallus. The general term plectenchyma
is used to designate all organized fungal tissues. Two types of
plectenchyma are prosenchyma, which is a
loosely woven tissue where the component hyphae lie mostly parallel to one
another and their typically elongated cells are easily distinguishable; and pseudoparenchyma which consists of closely
packed, generally isodimetric or oval cells that resemble the parenchyma
cells of higher plants. In this type
of tissue the hyphae have lost their individuality and are not
distinguishable as such (Plate 55). Conidia are small,
detachable bodies, either with one or more cells and capable of germinating. Catenulate
conidia are borne in chains.
They may become catenulate by continuous pinching-off of the end of
the conidiophore, or the first conidium may
divide giving rise to the second, and so on:
Sporangiospores are
common in the Phycomycota:
Zoospores (Planospores)
are characteristic of aquatic fungi:
Ascospores
are characteristic of the Ascomycota, although these also exhibit other
spore types.
Basidiospores are
characateristic of the Basidiomycota, although these also exhibit other spore
types:
All the noted spores are “walled structures”
except the zoospores Provost in 1807 first
observed a spore germinate from one fungus species. In the process of germination a spore must have a suitable
environment (water taken up). The
wall becomes thin in one or more places after water has been taken in.
In double-walled spores, the outer wall cracks on
germination.
Viability may be either long or short. Some spores are not durable at high
altitudes (high ultra-violet rays cause lethal mutagens). Sometimes simply the presence of an
element, e.g., Boron, will stimulate germination. In multicellular spores each cell can give rise to a mycelium.
------------------------------------------- In 1952 Alexopoulos gave a detailed narrative of Sexual
Reproduction in the fungi, which holds true into the 21st Century, and the
following description is derived therefrom [Alexopoulos, C. J. 1952.
Introductory Mycology.
John Wiley & Sons, NY. 482
p.].
The most common methods where
compatible nuclei are brought together (plasmogamy) are the following:
2. Gametangial
contact. In a large
number of fungi, the gametes of the male or of both the male and the female
gametangia have been reduced to undifferentiated protoplasts consisting
chiefly of a nucleus. Such gametes are never released from the gametangia to
the outside, but are transferred directly from one gametangium into the
other. In this method, two gametangia of opposite sex come in contact, and
one or more gamete nuclei migrate from the male to the female. In no case do
the gametangia actually fuse or in any way lose their identity during the sexual
act. The male nuclei, in some species, enter the female gametangium through a
pore developed by the dissolution of the gametangial walls at the point of
contact; in other species, an especially developed fertilization tube serves
as a passage for the male nuclei (Plate 60).
After the passage of the nuclei has been accomplished the oogonium continues
its development in various ways, and the antheridium eventually
disintegrates.
a.
Passage of the contents of one gametangium into the other through a
pore developed in the gametangial walls at the point of contact. This method is typical of some holocarpic
forms in which the entire thallus acts as a gametangium, the male thallus
attaching itself to and emptying its entire content into the female thallus (Plate 78f). b.
Direct fusion of the two gametangial cells into one. This takes place
by the dissolution of the contacting walls of the two gametangia, resulting
in a common cell in which the two protoplasts mix (Plate 61, 111g,
112g). 4. Spermatization. Some fungi bear numerous, minute,
uninucleate, spore-like, male structures termed spermatia that h are produced
in various ways. The spermatia are
carried by insects, wind, water, or (in some other way, to the female
gametangia or to special receptive hyphae, or even to somatic hyphae, to
which they become attached. A pore develops at the point of contact, and the
contents of the spermatium pass into the particular receptive structure that
serves as the female organ (Plate 62)
Sexual compatibility.
Although this phenomenon is certainly related to sex because it affects
sexual reproduction, compatibility should not be confused with sex. There are, for example, many fungi that
produce clearly distinguishable male and female sex organs on the same
thallus but in which, nevertheless, single individuals are sexually self-sterile because
their male organs are incompatible with their female organs and no
plasmogamy can take place. On the basis of sex, most fungi
may be classified into three categories: 1. Hermaphroditic, in which each
thallus bears both male and female organs.
Fungi in the above sex categories
belong to one or the other of the following two groups on the basis of compatibility: 1. Those in which every
thallus is sexually self-fertile, and can therefore reproduce sexually by
itself without the aid of another thallus.
------------------------------------------- Please see the following for additional examples of Fungal
Structures & Reproduction: Plate 1 = Fungal Vegetative
Body-1 Plate 2 = Fungal Vegetative
Body-2 Plate 3 = Examples of Fungus
Spores Plate 51 = Successive
growth stages of hypha: Gelasinospora
autosteira. Plate 52 = Somatic
hyphae. Plate 53 = Three types
of haustoria. Plate 54 = Two stages
in spore germination. Plate 55 = Fungal
tissues: Parenchyma & Pseudoparenchyma. Plate 56 = Stroma
& sclerotium: Daldinia sp.
& Claviceps purpurea Plate 57 = Asexual
reproduction: Fragmenting hypha: Collybia
conigena & Fusarium sp. Plate 58 = Asexual
reproduction: Budding Plate 58b = Various types of
fungal spores. Plate 59 = Sexual
reproduction: Planogametic
copulation: Catenaria sp., Allomyces arbuscula & Monoblepharella
taylori. Plate 60 = Sexual
reproduction: Plasmogamy thru'
gametangial contact in Pythium aphanidermatum. Plate 61 = Sexual
reproduction: Plasmogamy thru'
gametangial copulation in Sporodinia garndis. Plate 62 = Sexual
reproduction: Plasmogamy by
spermatization in Pleurage anserina. Plate 63 = Sexual
reproduction: Plasmogamy thru'
somatogamy in Peniophora sambuci. |
