Microorganism : Fungi, Classification, structure , general characteristics and morphology related to food

1. FUNGI

2. Five-kingdom system
 All life on earth is divided into five kingdoms:
 Plants
 Animals
 Fungi
 Protozoa
 Bacteria

3. FUNGI
 Fungi are eukaryotic microorganisms
Two major groups of organisms make up the
fungi.
 The multicellular filamentous fungi - molds
 The unicellular fungi - yeasts.
 Study of fungi – mycology
 Study of fungal diseases - mycoses

4. All molds are fungi but all fungi
are not molds--
yeasts are fungi but they are
unicellular and produce no aerial
mycelium
molds filamentous fungi that
produce aerial mycelium

5. The Kingdom of the Fungae
 Myceteae
 Great variety and complexity
 Approximately 100,000 species
 Majority are unicellular
or colonial

6. The Kingdom of the Fungae
Can be divided into three groups:
 Yeasts
 Molds
 Macroscopic Fungi

7. The Kingdom of the Fungae
Can be divided into three
groups:
 Molds
 Long, threadlike cells
 Filamentous arrangement
(hyphae)
 Some are dimorphic
(yeast-like and
filamentous forms exist)

8. The Kingdom of the Fungae
Macroscopic fungi
 Mushrooms, toad
stools
 Bracket fungi
 Stink horns

10. What is a Fungus?
To be considered a fungus, an organism
 Must be eukaryotic
 Possess cell walls
 Grow by extending filamentous cells called
hyphae, or by budding
 Obtain nutrients by releasing digestive enzymes
into the environment to break down organic
molecules, which are then absorbed
 Have no chlorophyll.
 cell walls have chitin.

12. Different forms of Fungi
 mushrooms
 rusts
 molds
 truffles
 yeast

13. GENERAL
CHARACTERSTI
CS OF FUNGI

14. General Characterstics
 Molds consist –long, branched, thread like filaments of cells called
hyphae.
 The total hyphal mass of a fungus is called as mycelium.
 The hyphae may be septate or aseptate (coenocytic)
 Many fungi are dimorphic in nature and change from a yeast form
to a mold form.
 They consist typical eukaryotic nuclei and membrane bound
organelles.
 The ribosomes are of 80s type.
 Most of the fungi are saprophytes and secure nutrients from dead
organic material.
 They grow best at optimum pH of 5.5 and optimum temperature of
20-350C.
 Fungi are aerobic in nature. Some yeasts are facultatively
anaerobic and carry out fermentation.

15. General Characterstics
 Majority of fungi are terrestrial. A few are fresh water or
marine.
 Some are parasitic and some are symbiotic.
 Many are pathogenic and cause several diseases.
 They are the important decomposers and breakdown the
organic matter.
 They lack chlorophyll and cannot carryout photosynthesis.
 They range in size from single-celled microscopic yeast to
multicellular molds and macroscopic puff balls and
mushrooms.
 They may be unicellular (yeasts) or multicellular and
filamentory ( molds).

16. General Characterstics
 Their primary storage material is glycogen which is a polysaccharide.
 They reproduce asexually, sexually or by both methods.
 The asexual reproduction occurs by the production of specific types of
spores such as arthrospores, chlamydospores, sporangiospores,
conidiospores, zoospores and blastospores.
 Some fungi exhibit binary fission type of reproduction.
 Sexual reproduction involves the union of two compatible nuclei or sex
organs or sex cells.
 They produce sexual spores such as ascospores, basidio spores, zygospores
and oospores.
 Some fungi produce useful substances such as penicillin, acetone, butanol
sorbitol etc.
 Some fungi produce antibiotic substances, eg. Penicillin.
 Fungi are usually filamentous.

17. FUNGI
 Fungi play a vital role in the environment
 economically important as a food source
 Cells of fungi are quite similar to those of plants, protists,
and animals.
 lack of chlorophyll separates them from plants.
 Since they do not ingest their food (by eating) they are
not animals.
 Most fungi reproduce through the generation of spores
(Mycelia sterilia being an exception).
 Fungal spores are non-motile (meaning they cannot
move of their own accord). This further separates fungi
from protists, which also can produce spores, but if they
do, they are often motile.

18.  Together with bacteria, fungi are the major
decomposers of organic materials in the soil.
 They degrade complex organic matter into
simple organic and inorganic compounds and
help recycle carbon, nitrogen, phosphorous,
and other elements for reuse by other
organisms.
 As molds grow by digesting the organic
material, they gradually destroy whatever they
grow on.
 Cause many plant and human diseases.

19. MOLDS
 Molds belong to the fungus family
 Molds are multicellular, filamentous fungi
 Moulds are microscopic, plant-like org’s,
 Growth can be easily recognised by it's cottony
appearance.
 Very common organisms that grow on food materials to
spoil the foods and can be easily be identified

24. Structure
 The thallus (body) of a mold consists of long
branching filaments of cells joined together; these
filaments are called hyphae (sing:hypha).
 Hyphae can grow to immense proportions. The hyphae
of a single fungus in Oregon extend across 3.5 miles.

28. Structure - Hyphae
 septate hyphae : Hyphae of most molds contain
cross-walls called septa which divide them into distinct,
uninucleate (one-nucleus) cell-like units --- septate
fungi
 coenocytic hypae : Hyphae of few classes of fungi
contain no septa and appear as long, continuous cells
with many nuclei. Cytoplasm passes through and
among cells of the hypha uninterrupted by cross walls -
-- coenocytic fungi.
 Even in fungi with septate hyphae, there are usually
openings in the septa that make the cytoplasm of
adjacent “cells” continuous; these fungi are actually

30. Structure - Hyphae
 Hyphae grow by elongating at the tips.
 Each part of hyphae is capable of growth, and when a
fragment breaks off, it can elongate to form a new
hyphae.
 In the laboratory, fungi are usually grown from
fragments obtained from a fungal thallus.
 Portion of a hyphae that obtains nutrients is called the
vegetative hyphae
 Portion concerned with reproduction is the
reproductive or aerial hypha, so named because it
projects above the surface of the medium on which
the fungus is growing.
 Aerial hypae often bear reproductive spores

31. Structure - Mycelium
 When environmental conditions are suitable,
the hypae grow to form a filamentous tangled
mass called a mycelium, which is visible to
the unaided eye .

33. Characteristics of Fungal Hyphae:
Septate versus Coenocytic

34. Mycelium: Large, Visible Mass of
Hyphae

35. GROWTH
 Molds release countless tiny microscopic cells
called spores, which spread easily through
the air and form new colonies where they find
the right conditions.
 For molds to grow and reproduce, they need
only a food source – any organic material,
such as leaves, wood, paper, or dirt – and
moisture (relative humidity > 60%).

36. Growth of mold
 Development of fungi cultures usually begins with
a spore.
 In the presence of moisture, the spore swells with
water much like a germinating Plant seed.
 Then the spore wall expands through a preformed
weak spot [the germ pore] to create a thin,
balloon-like protuberance.
 This first extension of growth is called a hypha
resembling long, worm-like structures.
 With continued growth, the hyphae will branch
and grow into a visible colony called a
"mycelium.“

38. FUNGI - NUTRITION
 All fungi are chemoheterotrophs, requiring organic
compounds for energy and carbon.
 Mostly saprophytes - obtain their nutrients from
dead organic matter.
 Play an important role in the environment by
decomposing and recycling organic matter.
 Few are parasitic on plants causing major losses of
crops.
 Others find their way into humans or other animals
and cause serious infections.

39. Nutrition of Fungi
The nutritional need of a fungus are facilitated by the
enzymes cellulase and/or
chitinase.
 Acquire nutrients by absorption
 Most are saprobes
 Some trap and kill microscopic soil-dwelling nematodes
 Haustoria allow some to derive nutrients from living plants and
animals
 Most are aerobic; some are anaerobic; many yeasts are facultative
anaerobes

40. NUTRITIONAL ADAPTATIONS
 Fungi are generally adapted to environments that
would be hostile to bacteria.
 Fungi are chemo heterotrophs, and, like bacteria, they
absorb nutrients rather than ingesting them as animals
do.
 Fungi differ from bacteria in certain environmental and
nutritional requirements
 Fungi usually grow better in an environment with a pH
of about 5, which is too acidic for the growth of most
common bacteria.
 Almost all molds are aerobic. Most yeasts are

41. NUTRITIONAL ADAPTATIONS
 Most fungi are more resistant to osmotic pressure
than bacteria; most can therefore grow in
relatively high sugar or salt concentrations.
 Fungi can grow on substances with a very low
moisture content, generally too low to support the
growth of bacteria.
 Fungi require somewhat less nitrogen than
bacteria for an equivalent amount of growth.
 Fungi are often capable of metabolizing complex
carbohydrates, such as lignin (a component of
wood), that most bacteria cannot use for
nutrients.

42. FUNGI - Genome
 Fungi have relatively very small nuclei, containing
very few nucleotides in their genomes.
 Example: the amount of nucleotides in mushrooms is
eight times that in E. coli (a prokaryote) but is only
1% of that in humans .

43. Cultural Characteristics
 Some molds look velvety on the upper surface
 some look dry and powdery
 some wet or gelatinous.
 Some molds are loose and fluffy
 some are compact.
 some are hard.
 Some possess pigments in their mycelium (red,yellow,
blue- green, brown, black, pink, orange etc)
 Mold growth on surfaces can often be seen in the
form of discoloration
 The appearance of the molds indicates its genus.

44. Physiological Characteristics
Temperature requirement –Most molds grow
well at ordinary temperature
Mesophilic and psychrotrophic range.
Optimum temperature = 25 to 30 c
but few grow well at 35 to 37c or
above(Aspergillus)
 A number of molds grow well at refrigeration and
freezing temperatures : -5 to -10c
 Few are thermophilic - can grow at a high
temperature.

45. Physiological Requirements
Moisture requirement – Aw of 0.6 -0.65
 Molds require less moisture to grow than yeast
and bacteria.
 If dried food has a moisture content below 14
to 15%, it will prevent or delay mold growth.
 Xerophilic molds use the humidity in the air as
their only water source; other molds need
more moisture

46. Physiological Requirements
 Oxygen Requirement –
 Molds are aerobic require oxygen for their growth.
 Fungi are aerobic or facultatively anaerobic,
anaerobic.
 pH :Grow over a wide range of pH(2-8.5) Majority
are favored by an acid pH.

47. Media
 In general can utilize many foods, ranging from
simple to complex.
 Most molds possess a variety of hydrolytic
enzymes and some are grown for their amylases,
pectinases, lipases and proteinases.

48. Identification
 Yeast identification, like bacterial identification,
involves biochemical tests. However, multicellular
fungi are identified on the basis of physical
appearance, including colony characteristics and
reproductive spores.

49. Where are molds found?
 Found in virtually every environment and can
be detected, both indoors and outdoors, year
round.
 Mold growth is encouraged by warm and
humid conditions.
 Outdoors - they can be found in shady, damp
areas or places where leaves or other
vegetation is decomposing.
 Indoors - they can be found where humidity
levels are high, such as basements or
showers

51. REPRODUCTION
 Fungi reproduce by the production of spores
 Fungal spores can be either asexual or sexual .
 Filamentous fungi can reproduce asexually by fragmentation of their
hyphae.
 Mold reproduce using both sexual and asexual reproduction methods.
 Molds reproduce through producing very large numbers of small spores,
which may contain a single nucleus or be multinucleate.
 Spores are formed from aerial hyphae
 Mold spores can be asexual (the products of mitosis) or sexual (the
products of meiosis)
 Many species can produce both types.
 Spores are of considerable importance in the identification of fungi
 At the end of the hyphae are the reproductive structures that produce
spores.
 Spores are produced on different structures depending on species.

52. Asexual and Sexual Reproduction in
fungi
 Telemorphs : The sexual fungi (perfect,
meiotic).
 They produce sexual spores.
 Anamorph: The asexual fungi (imperfect,
mitotic)
 Ex: Penicillium is an anamorph that arose from
a mutation in a telemorph.
 Holomorph: the whole fungus, including
anamorphs and teleomorph.
 many fungi can have both, especially
Ascomycota-- most have either one or the
other

58. Asexual Spores
 Asexual Spores are called conidia (sing:
conidium)
 When these spores germinate, they become
organism that are genetically identical to the
parent cell.
 Asexual spores are produced by the hypae
of an individual fungus through mitosis and
subsequent cell division
 There is no fusion of the nuclei of cells.

59. Asexual Spores
 Conidiospore/conidium (plural: conidia): Unicellular or multicellular
spores that are produced in a chain at the end of a conidiophores.
 Such spores are produced by Aspergillus.
 Conidia are not enclosed in a sac.
 Blastospores : blastoconidia are produced in a cluster by budding from a
parent cell (conidium).
 consists of buds coming off the parent cell.
 Such spores are found in yeasts, such as candidia albicans and
Cryptococcus.
 Sporangiospores: Spores 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.

64. Asexual Reproduction

65. sexual reproduction
 During sexual reproduction, compatible nuclei
unite within the mycelium and form sexual spores.
 Sexually opposite cells may unite within a single
mycelium, or different mycelia.
 When the cells unite, the nuclei fuse and form a
diploid nucleus.
 Several divisions follow, and the haploid state is
reestablished.

67. Sexual spores
 Sexual spores result from the fusion of nuclei
from two opposite mating strains of the same
species of fungus.
 Fungi produce sexual spores less frequently
than asexual spores.
 Organism that grow from sexual spores will
have genetic characteristics of both parental
strains.

68. Sexual Spores
 Fungal sexual spores results from sexual
reproduction which consists of three phases:
 Plasmogamy (Cell fusion): A haploid
nucleus of a donor cell (+) penetrates the
cytoplasm of a recipient cell (-).
 Karyogamy(Nuclear fusion): The (+) and (-)
nuclei fuse to form a diploid zygote nucleus.
 Meiosis. The diploid nucleus gives rise to
haploid nuclei (sexual spores), some of which
may be genetic recombinants.

69.  Oospores are produced when male gametes
(reproductive nuclei)enter a large spherical cell
(oogonium) and fertilize the eggs within.
 Ascospores are produced within spherical
cells called asci
 most often in groups of 4 or 8
 Usually the asci are produced within some kind
of enclosing structure and thus are not found
exposed on the hyphae.

71.  Zygospores :
 Do not occur inside any kind of enclosing
structure
 produced by the direct fusion of two hyphal
protrusions from neighbouring filaments.
 Usually zygospores are recognized as large,
nearly spherical, often dark brown or black,
rough-walled spores with two connecting
hyphae, representing the two mating
gametangia

73.  Basidiospores : produced externally on a
structure called a basidium. Basidia come in a
variety of forms, but those commonly
encountered on moulds will be club-shaped
and bear four or eight spores on sharp
projections at the apex.

75. Common Molds
 Absidia
 Alternaria
 Ascomycetes
 Aspergillus
 Basidiomycetes
 Cladosporium
 Curvularia
 Fusarium
 Mucor
 Penicillium
 Pithomyces
 Stachybotrys
 Trichoderma
 Ulocladium

76. Fungal spores - Bacterial
endospores
 Fungal spores are quite different from bacterial
endospores.
 Bacterial endospores allows a bacterial cell to survive
adverse environmental conditions.
 A single vegetative bacterial cell forms one endospore,
which eventually germinates to produce a single vegetative
bacterial cell. This process is not reproduction because it
does not increase the total number of bacterial cells.
 But after a mold forms a spore, the spore detaches from the
parent and germinates into a new mold. Unlike the bacterial
endospore, this is a true reproductive spore; a second
organism grows from the spore.
 Although fungal spores can survive for extended periods in
dry or hot environment, most do not exhibit the extreme
tolerance and longevity of bacterial endospores.

77. YEAST

79. Yeasts
 Yeasts are single-celled eukaryotic
microorganisms.
 Size: yeasts are 5 to 10 µm in diameter.
 They are larger than bacteria.
 Yeasts are non filamentous unicellular fungi.
 Typically spherical or oval in shape
 Yeasts consists single nucleus and eukaryotic
organelles.
 classified in the kingdom Fungi, with 1,500
species currently described.
 estimated to be 1% of all fungal species.

80. Yeast
Yeasts are very important economically:
- Yeasts are responsible for fermentation of beer and
bread. (Saccharomyces cerevisiae)
- Ethanol production
- Wastewater treatment:
a mixed culture of yeasts Candida lipolytic Candida
tropicalis, and Yarrowia lipolytica grown on
hydrocarbons or gas oil.

82. Cytological methods
 Unstained yeast cells can hardly be visualized by light
microscopy. At 1000 fold magnification, it may be
possible to see the yeast vacuole and cytosolic
inclusion bodies.
 By phase contrast microscopy together with an
appropriate staining technique, several cellular
structures can be distinguished.
 A very convenient tool to localize and even to follow
the movement of particular proteins within yeasts cells
is the use of the green fluorescent protein (GFP) from
the jelly fish (Acquorea Victoria) as a reporter
molecule.
 Organelle ultrastructure and macromolecular
architecture can only be obtained with the aid of EM.

83. Structure of Yeast Cell
 Yeast cells share most of the structural and
functional features of higher Eukaryotes — which
has rendered yeast an ideal model for Eukaryotic
cell biology.
 Ultrastructural features observed: Cell wall,
periplasm, Plasma membrane, bud scar,
cytoplasm, nucleus, mitochondria, Endoplasmic
reticulum, Golgi Apparatus, Secretory vesicles,
vacuole, peroxisomes.

84. Structure of Yeast Cell
 In contrast to mammalian cells, peculiarities of
yeast cells are that they are surrounded by a rigid
cell wall and develop birth scars during cell
division, the vacuole corresponds to lysosomes is
higher cells.
 Bud scars are specialized, ring –shaped convex
protrusions at the cell surface which remain on the
mother cells (of budding yeasts) after cell division
and birth of daughter cells. The concave
indentations remaining on the surface of the
daughter cell after budding are called birth scars.


85. Structure of Yeast Cell
 Yeast cytoplasm is an acidic (pH 5.25) colloidal fluid.
 Cytoskeleton comprises the microtubules and the
microfilament.
 Freely suspended 80s ribosomes
 Yeast nucleus is a round lobate organelle 1.5 μm in
diameter.
 yeast nuclear DNA can be isolated as linear molecules
ranging in size from 10 μm - 50 μm.
 Endoplasmic Reticulum is the site of bio synthesis and
modifications of proteins that are to be exported.

86. Structure of Yeast Cell
 From ER, proteins are directed to the Golgi Apparatus by
vesicles, which fuse at the Cis side and are exported from the
Golgi Apparatus at the trans side. In Golgi further
modifications of the protein by carbohydrate side chains may
take place.
 Proteins delivered from the Golgi are directed to different
destination within the cell or to the exterior via different
secretory vesicles to the vacuole, the bud region during
mitosis, the plasma membrane , the periplasm.
 Peroxisomes (membrane-enclosed organelles that contain
enzymes involved in a variety of metabolic reactions,
including several aspects of energy metabolism) perform a
variety of metabolic functions in Eukaryotic cells.
 Mitochondria – under aerobic conditions, yeast mitochondria
are involved in ATP synthesis coupled to oxidative
phosphorylation

87. Yeasts
 Like molds, yeasts are widely distributed in
nature; they are frequently found as a white
powdery coating on fruits and leaves.

88. Reproduction
 Most yeasts reproduce asexually.
 Yeasts grow as single cells producing daughter cells
either by
an asymmetric division process called Budding - the
budding
yeasts or by
 Binary fission (splitting in two) - the fission yeasts.
 Budding: a small bud cell forms on the cell, which
gradually enlarge and separate from the mother
cells.
 Most of the yeasts reproduce by budding.

90. Budding
 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.
 Yeasts reproduce rapidly. One yeast cell can in time
produce up to 24 daughter cells by budding.
 Budding yeasts divide unevenly (Saccharomyces)

91. Budding

93. Bud Scar

94. Bud Scar

95. Pseudohypha
 Some yeasts produce buds that fail to detach
themselves; these buds form a short chain of cell
called a pseudohypha.
 Candida albicana attaches to human epithelial cells
as a yeasts but usually requires pseudohypha to
invade deeper tissues

97. Fission: similar to budding
During this parent cells elongates, grow to
certain size its nucleus divides, and two
equal daughter cells are produced.
Only a few yeast species reproduce by
fission. e.g. Schizosaccharomyces
 divide evenly to produce two new cells.

100. Yeast respiration
 Yeasts are facultative anaerobes, which allows them to
grow in a variety of environments.
 When oxygen is available, they carry out aerobic respiration.
 When oxygen is not available, they ferment carbohydrates to produce
ethanol and carbon dioxide.
 Yeasts can use oxygen or an organic compound as the final electron
acceptor; this is valuable attribute because it allows these fungi to survive
in various environments.
 If given access to oxygen, yeasts perform aerobic respiration to metabolize
carbohydrate to 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. Saccharomyces species produce ethanol in brewed beverages
and Co2 for leavening bread dough .

101. Morphology
 Yeast size can vary greatly depending on the species,
typically measuring 4 -12 µm long and 3–4 µm in
diameter, although some yeasts can reach over 40 µm
in diameter.
 spherical or oval in shape
 some species of yeast forms may become multicellular
through the formation of strings of connected budding
cells known as pseudohyphae as seen in most molds

102. Nutrition and growth
 Yeasts are chemoorganotrophs, as they use organic
compounds as a source of energy and do not require
sunlight to grow.
 Carbon is obtained mostly from hexose sugars, such
as glucose and fructose, or disaccharides such as
sucrose and maltose.
 Some species can metabolize pentose sugars such as
ribose, Xylose
 Some species can metabolize alcohols and organic
acids.
 Yeast species require oxygen for aerobic cellular
respiration (obligate aerobes) or are
anaerobic(fermentative yeast), facultative anaerobes.

103. Cultural Characterstics
 yeasts are grown in the laboratory on solid growth
media or in liquid broths.
 They grow especially well in substances containing
sugar.
 Increase in the number of yeasts cells on a solild
medium produce a colony similar to a bacterial colony.
 Common media used for the cultivation of yeasts
include
 potato dextrose agar or potato dextrose broth
 Wallerstein Laboratories nutrient agar
 yeast peptone dextrose agar

104. Cultural Characterstics
 Temperature:
 Yeasts vary in temperature range they grow best.
 Optimum = 25 to 30c
 Maximum about 35 to 47c
 Some grow at 0c or less
 pH : 4 to 4.5
 Yeasts grow best in a neutral or slightly acidic Ph
 Will not grow well in alkaline medium unless
adapted to it.

105. Cultural Characterstics
 Water activity/moisture : 0.7 to 0.8
 Osmophilic yeasts can grow at even low aW.
 Require less moisture than majority of bacteria
and more moisture than molds.
 Can grow in the presence of high concentration
of solutes(sugar/salt)

106. Cultural Characterstics
 They differ from most fungi, which grow as
thread-like hyphae. But this distinction is not a
fundamental one, because some fungi can
alternate between a yeast phase and a hyphal
phase, depending on environmental
conditions. Such fungi are termed dimorphic

107. Cultural characteristics
 For the most part, the appearance of massed yeast growth is not
useful in the identification of yeasts, although growth as a film on the
surface of liquid media suggests an oxidative or film yeast.
 Some produce pigments (carotenoid pigment indicates the genus
Rhodotorula) - causes colored spots on foods.
 It is difficult to tell yeast colonies from bacterial ones on agar plates;
the only certain way is by means of microscopic examination of the
organisms.
 Most young yeast colonies are moist and somewhat slimy but may
appear mealy; most colonies change little with age and become dry
and wrinkled.
 Yeasts are oxidative, fermentative, or both. The oxidative yeasts may
grow as a film, pellicle, or scum on the surface of a liquid and then
are termed film yeasts.
 Fermentative yeasts usually grow throughout the liquid and produce
carbon dioxide.

108. Fungi -dimorphic
 Some fungi, most notably the pathogenic species, exhibit
dimorphism—two forms of growth. Such fungi can grow
either as a mold or as a yeasts.
 They have the ability to shift from the yeast form to the
mold form and vice versa.
 Many fungal pathogens exist in the body in the yeast form
but revert to the mold form in the laboratory when
cultivated.
 The mold like forms produce vegetative and aerial
hyphae; the yeast like forms reproduce by budding.
 Dimorphism in pathogenic fungi is temperature-
dependent: at 370C, the fungus is yeast like, and at 250C,
it is mold like. However, the appearance of the dimorphic
fungus changes with CO2 concentration.

109. Fungal Infections
 These infections are occurring as nosocomial
infections and in people with compromised
immune systems. In addition, thousands of
fungal disease afflict economically important
plants, costing more than one billion dollars
annually.

110. Fungi are also beneficial
 They are important in the food chain because they
decompose dead plant matter, thereby recycling vital
elements.
 Through the use of extracellular enzymes such as cellulases,
fungi are the primary decomposers of the hard parts of plants,
which cannot be digested by bacteria and animals.
 Nearly all plants depend on symbiotic fungi, known as
mycorrhizae, which help their roots absorb minerals and
water from the soil.
 Fungi are also valuable to animals.
 Fungi-farming ants cultivate fungi that break down cellulose
and lignin from plants, providing glucose that the ants can
then digest.
 Fungi are used by humans for food (mushrooms) and to
produce foods (bread and citric acid) and drugs (alcohol and
penicillin).
 Of the more than 100,000 species of fungi, only about 200 are

111. The Significance of Fungi
 Decompose dead organisms and
recycle their nutrients
 Form associations with roots of
vascular plants, which help plants
absorb water and minerals
 Used for food, in religious
ceremonies, and in manufacture of
foods and beverages
 Produce antibiotics
 Serve as important research tools
 30% cause diseases of plants,
animals, and humans
 Can spoil fruit, pickles, jams, and
jellies

112. Many fungi are very useful to
humans
 yeasts-- baking and brewing
 antibiotics--- e.g. penicillin & cephalosporin
 other drugs-- e.g. cyclosporin
 many organic acids are commercially
produced with fungi-- e.g. citric acid in Coke is
produced by an Aspergillus
 steroids and hormones--- e.g. the pill
 certain “stinky” cheeses-- e.g. blue cheese,
Roquefort and Camembert

113.  Fungi are important experimental/model org’s for
genetics, cell biology and molecular biology!
 easily cultured, occupy little space, multiply rapidly,
short life cycle.
 study metabolite pathways ,growth, development,
and differentiation
 mechanisms of cell division and development
 microbial assays of vitamins and amino acids