Fungi are a diverse group of eukaryotic organisms separate from plants and animals, with over 100 thousand identified species, 200 of which are pathogenic. They can exist in multicellular forms (molds) or unicellular forms (yeasts), and reproduce through both asexual and sexual means, producing various types of spores. Fungi play significant ecological roles as decomposers and have considerable economic importance in food production and pharmaceuticals, alongside harmful effects like mycoses, which are chronic fungal infections.

2. Introduction
o Fungi are a large, diverse and widespread group of organisms that include
microorganisms such as molds, yeasts and mushrooms. These organisms are
classified as a kingdom which is separate from other eukaryotic life kingdom of
plants and animals.
o More than 100 thousand species of fungi have been identified by biologists. It
is estimated that more than 1.5 million species currently exist on earth. Among
them 200 are pathogenic.
o More than 1 billion dollar loss for fungi annually.
o Study of fungi is called mycology.

4. Characteristics of Fungi
o Eukaryotic
o Have no chlorophyll – non photosynthetic.
o Cell wall composed of special component called chitin.
o Most multicellular (hyphae), some unicellular (yeast).
o Non motile.
o Are more related to animals than plant kingdom.
o Lack true roots, leaves and stems.
o Absorptive heterotrophs – Digest food externally and then absorb it.
o Decomposers
o Can grow in any direction.
o Can invade the interior of a substrate with absorptive filaments.

5. Vegetative structure
Molds and yeasts
o The thallus (body) of a mold or fleshy fungus consists of long filaments of cells joined together; these
filaments are called hyphae (singular: hypha) which can extend over 4 square miles.
o In most molds, the hyphae contain cross-walls called septa (singular: septum), which divide them into
distinct, uninucleate (one-nucleus) cell-like units. These hyphae are called septate hyphae.
o In a few classes of fungi, the hyphae contain no septa and appear as long, continuous cells with many
nuclei. These are called coenocytic hyphae.

6. o Hyphae grow by elongating at the tips. Each part of a hypha is capable of growth, and when a fragment
breaks off, it can elongate to form a new hypha.
o The portion of a hypha that obtains nutrients is called the vegetative hypha.
o The portion concerned with reproduction is the reproductive or aerial hypha. Aerial hyphae often bear
reproductive spores. When environmental conditions are suitable, the hyphae grow to form a
filamentous mass called a mycelium, which is visible to the unaided eye.

7. Yeasts
o Yeasts are non filamentous, unicellular fungi that are typically spherical or oval.
o Like molds, yeasts are widely distributed in nature; they are frequently found as a white powdery coating
on fruits and leaves.
o Budding yeasts, such as Saccharomyces, divide unevenly. In budding, the parent cell forms a
protuberance (bud) on its outer surface. As the bud elongates, the parent cell’s nucleus divides, and one
nucleus migrates into the bud. Cell wall material is then laid down between the bud and parent cell, and
the bud eventually breaks away. One yeast cell can in time produce up to 24 daughter cells by budding.
Some yeasts produce buds that fail to detach themselves; these buds form a short chain of cells called a
pseudohypha. Ex: Candida albicans.

8. o Fission yeasts, such as Schizosaccharomyces, divide evenly to produce two new cells. During fission,
the parent cell elongates, its nucleus divides, and two offspring cells are produced.
o Yeasts are capable of facultative anaerobic growth, which allows these fungi to survive in various
environments. If given access to oxygen, yeasts perform aerobic respiration to metabolize
carbohydrates into carbon dioxide and water; denied oxygen, they ferment carbohydrates and
produce ethanol and carbon dioxide. This fermentation is used in the brewing, wine-making, and
baking industries.
Dimorphic Fungi
o Some fungi, most notably the pathogenic species, exhibit
dimorphism—two forms of growth. Such fungi can grow
either as a mold or as a yeast.
o The moldlike forms produce vegetative and aerial hyphae;
the yeastlike forms reproduce by budding.
o Dimorphism in pathogenic fungi is temperature
dependent: at 37°C, the fungus is yeastlike, and at 25°C, it
is moldlike.
o In the most case of non pathogenic fungi, dimorphism
depends on CO2 concentration.

9. Life Cycle of Fungi
Both sexual and asexual reproduction in fungi occurs by the formation of spores.
Asexual spores
o Asexual spores are produced by an individual fungus through mitosis and subsequent cell division. Two
types of asexual spores are produced by fungi. One type is a conidiospore and another type is
sporangiospore.
 Conidiospore
 Conidiospore, or conidium (plural: conidia), a unicellular or multicellular spore that is not enclosed
in a sac. Conidia are produced in a chain at the end of a conidiophore. Such spores are produced by
Penicillium and Aspergillus. Few types of conidiospores are –
 Arthroconidia: Arthroconidia are single, slightly thicked walled spores formed by the fragmentation
of a septate hypha. One species that produces such spores is Coccidioides immitis.
 Blastoconidia: Blastoconidia are formed from the buds of its parents cells. Such spores are found in
some yeasts such as Candida albicans and Cryptococcus.
 Chlamydoconidia: chlamydoconidia are thick-walled spore formed by rounding and enlargement
within a hyphal segment. A fungus that produces chlamydoconidia is the yeast Candida albicans.

11.  Sporangiospore
 The other type of asexual spore is a sporangiospore, formed within a sporangium, or sac, at the end of
an aerial hypha called a sporangiophore. The sporangium can contain hundreds of sporangiospores.
Such spores are produced by Rhizopus.
Sexual spores
A fungal sexual spore results from sexual reproduction, which consists of three phases:
o Plasmogamy : A haploid nucleus of a donor cell (+) penetrates the cytoplasm of a recipient cell (-).
o Karyogamy : The (+) and (-) nuclei fuse to form a diploid zygote nucleus.
o Meiosis : The diploid nucleus gives rise to haploid nuclei (sexual spores), some of which may be genetic
recombinants.

13. Nutritional Adaption of Fungi
o Fungi usually grow better in an environment with a pH of about 5, which is too acidic for the growth of
most common bacteria.
o Almost all molds are aerobic. Most yeasts are facultative anaerobes.
o Most fungi are more resistant to osmotic pressure than bacteria; most can therefore grow in relatively
high sugar or salt concentrations.
o Fungi can grow on substances with a very low moisture content, generally too low to support the
growth of bacteria.
o Fungi require somewhat less nitrogen than bacteria for an equivalent amount of growth.
o Fungi are often capable of metabolizing complex carbohydrates, such as lignin (a component of wood),
that most bacteria can’t use for nutrients.

14. Medically Important Fungi
Zygomycoya
o Conjugation fungi
o Saprophytic molds
o Coenocytic hyphae
o Asexual spore : Sporangiospore
o Sexual spore : Zygospore (when the nuclei of two cells that are morphologically similar to each other fuse)

16. Microsporidia
o Unusual eukaryotes because they lack mitochondria.
o They also don’t have microtubules.
o Obligate intracellular parasites.
o Sexual reproduction has not been observed but probably occurs within the host.
o Causes human diseases such as diarrhea, keratoconjunctivitis.

17. Ascomycota
o Sac fungi
o Include molds and yeasts
o Septate hyphae
o Asexual spore : Conidiospore
o Sexual spore : Ascospore (when the nuclei of two cells that can be either morphologically similar or
dissimilar fuse)
o The members of this phylum are called sac fungi because of the ascus.

18. Basidiomycota
o Club fungi
o Septate hyphae
o Includes mushrooms
o Asexual spore : Conidiospore
o Sexual spore : Basidiospore
o Four basidiospores per basidium

19. Fungal Diseases
Any fungal infection is called a mycosis. Mycoses are generally chronic (long-lasting) infections because
fungi grow slowly. Mycoses are classified into five groups.
Systemic mycoses
o Systemic mycoses are fungal infections deep within the body.
o Caused by soil fungi.
o The spores are transmitted by inhalation; these infections typically begin in the lungs and then spread
to other body tissues.
o They are not contagious from animal to human or from human to human.
o Examples : Histoplasmosis, Coccidioidomycosis.

20. Subcutaneous mycoses
o Subcutaneous mycoses are fungal infections beneath the skin.
o Caused by saprophytic fungi that live in soil and on vegetation.
o Infection occurs by direct implantation of spores or mycelial fragments into a puncture wound in the skin.
o Example: Mycetoma, sporotrichosis etc.
Cutaneous mycoses/ Dermatomycoses
o Infect only the epidermis, hair, and nails.
o Dermatophytes secrete keratinase (an enzyme that degrades keratin).
o Infection is transmitted from human to human or from animal to human by direct contact or by contact
with infected hairs and epidermal cells.
o Example: Tinea corporis, Tinea paedis etc.

21. Superficial mycoses
o Localized along hair shafts and in superficial (surface) epidermal cells.
o The superficial mycoses are usually confined to the outermost layer of skin, hair, mucosa and do not invade
living tissues.
o These infections are prevalent in tropical climates.
o Example: Pityriasis versicolor, Tinea nigra etc.
Opportunistic mycoses
o An opportunistic pathogen is generally harmless in its normal habitat but can become pathogenic in a
host who is seriously debilitated or traumatized, who is under treatment with broad-spectrum
antibiotics, whose immune system is suppressed by drugs or by an immune disorder, or who has a lung
disease.
o Example: Pneumocystis is an opportunistic pathogen in individuals with compromised immune systems
and is the most common life-threatening infection in AIDS patients.

22. Economic Effects of Fungi
o Fungi has been used to produce citric acid for foods and beverages since 1914. Example : Aspergillus niger.
o The yeast Saccharomyces cerevisiae is used to make bread, wine, hepatitis B vaccine.
o Trichoderma is used commercially to produce the enzyme cellulase, which is used to remove plant cell walls to
produce a clear fruit juice.
o Taxomyces produces taxol (Anticancer drug).
o A foam filled with Paecilomyces fumosoroseus is being used as a biological alternative to chemicals to kill termites
hiding inside tree trunks and other hard-to-reach places.
o Coniothyrium minitans are used to kill fungi on crops.
Beneficial effect
Harmful effect
o Mold spoilage of fruits, grains, and vegetables is relatively common, but bacterial spoilage of such foods is not.
There is little moisture on the unbroken surfaces of such foods, and the interiors of fruits are too acidic for many
bacteria to grow there. Jams and jellies also tend to be acidic, and they have a high osmotic pressure from the
sugars they contain. These factors all discourage bacterial growth but readily support the growth of molds.