fungi
It has been duly observed and amply demonstrated that
fungi invariably grow as single cells, as
in
yeast, or as multicellular filamentous colonies, as in molds and mushrooms. Interestingly, fungi do
not contain
chlorophyll (i.e., the nature’s organic green matter), hence they are saprophytic (i.e., they
obtian food from dead organic matter) or
parasitic (i.e., they obtain nourishment from the living organisms),
and above all the body’s normal flora categorically contains several
fungi. However, most fungi
are
not pathogenic in nature.
Importantly, the
fungi that essentially cause disease belong to a specific group known as fungi
imperfecti
. In immunocompetent humans these fungi usually cause minor infections of the hair, nails,
mucous membranes
, or skin. It is, however, pertinent to mention here that in a person having a compromised
immune system
due to AIDS or immunosuppressive drug therapy, fungi critically serveas a source of the viable opportunistic infections that may even cause death ultimately.
Another school of thought defines
fungi as — ‘those microorganisms that are invariably
nucleated, spore-bearing and do not possess chlorophyll, generally reproduce both asexually and
sexually, and have somatic structural features that are essentially surrounded by cell walls comprising
of polysaccharides, cellulose and/or chitin, mannan, and glucan.
In fact,
fungi are considered to be mostly saprophytic, making use of dead organic matter as a
source of energy
, vital natural organic decomposers, and destroyers of food stuffs. While a major
segment of species happen to be
facultative parasites that specifically able to feed upon either live or
dead organic matter, and a relatively minor quantum of species may only survive on the
living
protoplasms
. These fungi are designated as obligate parasites thereby overwhelmingly causing disease
of man, animals, and plants. They also prove to be of reasonably great economic and medical
importance.
Industrial Research
— Certain fungi are intimately associated with the manufacture of bread,
beer
, and wines (fermentative procedures) ; production of edible varieties of cheese, vitamins, and
organic acids (
viz., lactic acid, citric acid, acetic acid etc.) ; and several ‘antibiotics’.
Biological Research
— Geneticists and Biochemists exploit the fungi profusely by virtue oftheir extraordinarily unique reproductive cycles, but having a rather relatively simple metabolism.
Reproduction (Cultivation) of Fungi
A large number of
fungi invariably get reproduced both asexually and sexually. Nevertheless,
the ensuing
morphology, and the cycle of these reproductive structures is employed extensively in
carrying out their elaborated and logical
classification.
Asexual Reproduction
The most common procedure of
asexual reproduction is usually accomplished by the help of
spores
. In common practice most of them are found to be colourless (hyaline), while a few of them are
duly pigmented as green, yellow, red, orange, black or brown. In fact, their size may invariably range
from small to large and their shape from
globose via oval, oblong, needle-shaped to helical. Virtually,
the ensuing infintie variation in adequate spore appearance and their arrangement prove to be of immense
utility for
proper identification. Asexual reproduction may be borne particularly in a sac-likestructure termed as sporangium ; and the spores being referred to as sporangiospores being called
Salient Features :
The salient features related to asexual reproduction are as follows :
(1) The simplest form of available fungal spore is known as the
zoospore, which possess no rigid
cell wall, and is duly propelled by flagella.
(2) Flagellum is usually found to be much more complex than that observed in bacteria.
(3)
Flagellum is made up of 11 parallel fibrils, of which 9 forming a cylinder and 2 placed
centrally
.
(4) Base of
flagellum enters the cell and gets attached to the nucleus by a structure termed as
rhizoplast
.
(5)
Flagellum structure (9 + 2 fibrils) is usually found to be fairly consistent with that shown
for other
flagellated organisms.
(6)
Sporangium designates the asexual reproductive structure pertaining to these aquatic
fungi
. In its early stages it is found to be loaded with nuclei and protoplasm.
(7) Cleavage takes place subsequently whereby the numerous sections invariably get developed
into the corresponding
uninucleate zoospores.
(8) Finally, following a motile phase, the resulting zoospore encysts, losing its
flagellum, and
rests quietly just prior to
germination.
Sexual Reproduction
Importantly, the
sexual reproduction is characterized by the strategical union of two compatible
nuclei
; and the entire phenomenon may be distinctly divided into three phases, namely :
Phase I :
The union of the gametangia (i.e., sex-organs) brings the nuclei into close proximity
within the same protoplast. It is also referred to as
plasmogamy.
Phase II :
It is known as karyogamy, which takes place with the fusion of two nuclei. It has been
duly observed that in the
lower fungi the said two processes may take place in immediate sequence ;
whereas, in the
higher fungi they do occur at two altogether different time periods in the course of their
life-cycle
.
Phase III :
It is known as meiosis that essentially takes care of the nuclear fusion whereby the
actual number of the
chromosomes is distinctly and significantly reduced to its original haploid state.
Industrial Importance of Fungi
There are several vital and important
industrial importance of fungi, which shall be enumerated
briefly as under :
Production of Wines and Beer
Natural yeasts
have been employed over the centuries in Italy and France, to ferment fruit
juices
(wines) or cereal products viz., malt (silent alcohol) in the commercial production of various
types of world-class whiskies, rums, vodkas, brandies, gins, and the like. The high-tech industrial manufacturers
of today largely make use of the critical and effective pasteurization of the yeast
Saccharomyces
cerevisiae
.
In the production of wine and beer, the lower temperature favours the fermentation of yeast.
Under these circumstances the
organisms (bacteria) are usually discouraged due to two major reasons,
namely :
(
a) acidity of the fermentation medium, and(b) addition of hops that exert a mild inhibitory action to the microorganisms.
Thus, the fermentation invariably takes place under the
anaerobic conditions thereby giving
rise to the production of
alcohol (i.e., ethanol).
Examples :
Following are certain typical examples of alcohols commonly used in the manufacture
of
‘alcoholic beverages’, such as :
(
i) Silent Spirits — Spirits obtained by the fractional distilation of alcohol produced by fruit or
cereal fermentation.
(
ii) Brandy — obtained from wine.
(
iii) Whisky — obtained from malted cereals (Barley).
(
iv) Rum — obtained from fermented molasses (i.e., a by product from sugar-industry
containing unrecoverable sugar upto 8–10%).
Production of Bakery Products
The baker, strain of
Saccharomyces cerevisiae are meticulously selected for their specific high
production of CO
2 under the aerobic parameters. In actual practice, the Baker’s Yeast is particularly
manufactured for
bread-making, and is available commonly as ‘dried yeast’ or ‘compressed yeast’.
These also find their abundant use as a
food supplement by virtue of the fact that are fairly rich in
Vitamin B variants
.
Production of Cheeses
There are certain
typical fungi which are specifically important in the manufacture of cheeses.
Example
: The mould Penicillium roqueforti is usually employed in the production of the blueveined
cheeses
. In actual practice, the spores of the fungus are normally used to inoculate the cheese,
that is subsequently
‘ripened’ at 9°C in order to discourage the very growth of organisms other than the
Penicillium
. Because, the moulds happen to be of aerobic nature, adequate perforations are carefully
made in the main bulk of the cheese so as to allow the passage of air to gain entry. However, the
decomposition of fat takes place to impart these cheeses a
characteristic flavour.
Interestingly, the mould
Penicillium comemberti grows very much on the surface of the cheese,
and develops inwards producing the characteristic liquefaction and softening of the surface,
i.e., incontrast to the aforesaid P. roqueforti that grows within the body of the cheese.