Fungi

Fungi

• These are spore-bearing organisms such as yeast, mold, and mushrooms that obtain simple organic compounds by absorption.

• They have no chlorophyll and reproduce both sexual and asexual means.

• They are inconspicuous because of the small size of their structures and their cryptic lifestyles in soil, on dead matter, and as symbionts of plants, animals, or other organisms.

Mycology

The study of fungi

Mycoses

The study of fungal diseases

Fungi

• Together with bacteria, they are the major decomposers of organic materials in the soil.

• They degrade complex organic matter into simple organic and inorganic compounds.

• In doing this, they help recycle carbon, nitrogen, phosphorus, and other elements for reuse by other organisms.

• Some of these organisms can cause superficial, cutaneous, subcutaneous, systemic, and many plant diseases.

nuclei

Fungal cells contain membrane-bound __________ with chromosomes that contain DNA.

chloroplasts

Fungi lack __________ and are heterotrophic organisms, requiring preformed organic compounds as energy sources.

chemoheterotrophic; saprophytes

Fungi are _________ organisms and are __________.

5

Fungi grow best where there is a rich supply of organic matter (sugar) and grow at an acidic pH of about _____. Growth rate is slower than bacteria.

spores

Fungi reproduce by both asexual and sexual means using __________.

hyphae

The cells of most fungi grow as tubular, elongated, and thread-like (filamentous) structures called __________.

budding

Some fungal species grow as single-celled yeasts that reproduce by __________.

Dimorphic fungi

__________ can switch between a yeast phase and a hyphal phase in response to environmental conditions.

glucans and chitin

The fungal cell wall is composed of __________; while the former compounds are also found in plants and the latter in the exoskeleton of arthropods.

sterol ergosterol

The cell membrane of fungi contains __________.

25; 37

Most fungi grow at about _____ degrees Celsius except for pathogens, which grow at _____ degrees Celsius.

aerobic

Most fungal species are __________ except for fermentation yeasts that grow in both aerobic and anaerobic environments.

molds; yeasts

The filamentous fungi are called __________, while the unicellular fungi are called __________.

Molds

Consist of long, branching filaments of cells called hyphae

hyphae

• Molds consist of long, branching filaments of cells called __________.

• These are cylindrical, thread-like structures that are 2-10 micrometers in diameter and are up to several centimeters in length.

branching

New hyphae are typically formed by emergence of new tips along existing hyphae by a process called __________, or occasionally growing hyphal tips bifurcate (fork) giving rise to two parallel-growing hyphae.

Mycelium

• A tangled mass of hyphae visible to the unaided eye

• An interconnected network of hyphae

coenocytic fungi

In some molds, the cytoplasm passes through and among cells of the hypha uninterrupted by cross walls. These fungi are said to be __________.

septate fungi

Those fungi that have cross walls are called __________.

Conidia

This is the spore structure in fungi.

1. Hypha

2. Conidiophore

3. Phialide

4. Conidia

5. Septa

Yeasts

These are microscopic, unicellular fungi with a single nucleus and eukaryotic organelles.

budding

• Yeasts reproduce asexually by a process of __________.

• In this process, a new cell forms at the surface of the original cell, enlarges, and then breaks free to assume an independent existence.

Dimorphic fungi

The ability of some species of fungi 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.

spores

• Reproduction in fungi usually involves _________.

• These are produced either sexual or asexual means.

• These are important in the identification and classification of the fungus, since the spores are unique in shape, color, and size.

• A single one of these is capable of germinating and reestablishing the entire mycelium.

• They are also the method for spreading fungi in the environment.

Asexual reproduction

• Occurs in the fungi when spores form by mitosis

• These spores can be conidia (conidiospore), sporangiospores, arthrospores (fragments of hyphae), or chlamydospores (spores with thick walls)

• Allows more rapid dispersal than sexual reproduction

Sexual reproduction

• Occurs through meiosis in all fungal phyla (except the Deuteromycota)

• Most fungi have both a haploid and diploid stage in their life cycles. In sexually reproducing fungi, compatible nuclei unite by fusing their hyphae and form sexual spores. Sexually opposite cells may unite within a single mycelium, or different mycelia may be required. When the cells unite, the nuclei fuse and form a diploid nucleus. Several divisions follow, and the haploid state is reestablished.

• Sexual spores are ascospores, zygospores, and basidiospore.

Deuteromycota

This is an informal group of unrelated fungi that all share common features and use strictly asexual reproduction.

Chytridiomycota

• Commonly known as chytrids

• The simplest and most primitive true fungi (eumycota)

• Distributed worldwide

• Most are unicellular and have chitin in their cell wall

• A few form multicellular organisms and hyphae with no septa

Chytridiomycota

• Produce zoospores that are capable of active movement through aqueous phases with a single flagellum

• Its ecological habitat and cell structure have much in common with protists

• Usually live in aquatic environments, although some species live on land

• Some species thrive as parasites on plants, insects, or amphibians, while others are saprobes

• e.g. Chytridium olla

Zygomycota

• Known as zygomycetes (conjugated fungi)

• A relatively small group of fungi

• Produce sexual spores called zygospores

• Produce asexual spores called sporangiospores

Rhizopus stolonifer

• A fungus found on fruits, vegetables, and breads.

• It is the familiar bread mold.

• It anchors itself to the subtratum with special hyphae known as rhizoids.

Rhizopus

This is used in the industrial production of steroids, meat tenderizers, industrial chemicals, and certain coloring agents.

Ascomycota

• Commonly known as sac (ascus) fungi or ascomycetes

• Constitutes the largest taxonomic group within the Eumycota

• Form sexual spores called ascospores

• Form asexual spores called conidiospores

• Many of these are of commercial importance

• Also includes a few mushrooms and many filamentous fungi living as saprotrophs, parasites, and mutualistic symbionts

Ascospores

• The sexual spore of ascomycota

• Enclosed in a special sac-like structure called an ascus

Yeasts (Saccharomyces)

This is used in baking, brewing, and wine fermentation, plus truffles and morels, which are held as gourmet delicacies.

Aspergillus oryzae

This is used in the fermentation of rice to produce sake.

Basidiomycota

• Commonly known as the club fungi or basidiomycetes

• Produce sexual spores called basidiospores

• Asexual reproduction occurs by budding, fragmentation, or conidia formation

• Most common mushrooms (edible) belong to this group

• Includes shelf fungus, which cling to the bark of trees like small shelves

• Includes smuts and rusts, which are important plant pathogens

basidia

Basidiomycota produce sexual spores called basidiospores on club-like stalks called __________, which are the swollen terminal cell of a hypha.

Glomeromycota

• A newly established phylum which comprises about 230 species that all live in close association with the roots of trees, forming arbuscular mycorrhizae

• Reproduce asexually

• Formerly part of the Zygomycota and was elevated to phylum status in 2001

Arbuscular mycorrhizae

This is a form of symbiosis wherein fungal hyphae interact with the root cells, forming a mutually beneficial association where the plants supply the carbon source and energy in the form of carbohydrates to the fungus, and the fungus supplies essential minerals from the soil to the plant.

Deuteromycota

• Also known as deuteromycetes

• These fungi lack a known sexual cycle and are said to be “imperfect fungi”

• Asexual reproduction occurs by means of conidia

• When its sexual cycle is discovered, a fungus from this division is usually reclassifed in one of the other divisions.

• e.g. organisms of athlete’s foot and ringworm

Lichens

• Formed by a symbiotic relationship between algae or cyanobacteria and fungi (mostly various species of ascomycetes and a few basidiomycetes), in which individual photobiont cells are embedded in a tissue formed by the fungus

• Occur in every ecosystem on all continents, play a key role in soil formation and the initiation of biological succession, and are the dominating life forms in extreme environments, including polar, alpine, and semiarid desert regions

• They are able to grow on inhospitable surfaces, including bare soil, rocks, tree bark, wood, shells, barnacles, and leaves. As in mycorrhizas, the photobiont provides sugars and other carbohydrates via photosynthesis, while the fungus provides minerals and water.

Penicillin G

• Produced by Penicillium chrysogenum

• A structurally related group of B-lactam antibiotics that are synthesized from small peptides

Ciclosporin

This is commonly used as an immunosuppressant during transplant surgery.

Fusidic acid

This is used to help control infection from methicillin-resistant Staphylococcus aureus.

lentinan

The shiitake mushroom is a source of __________, a clinical drug approved for use in cancer treatments in several countries.

Psilocybin mushrooms

• Magic mushrooms

• Ingested for their psychedelic properties, both recreationally and religiously

Magnaporthe oryzae

Serious pathogens of many cultivated plants causing extensive damage and losses to agriculture and forestry include the rice blast fungus __________.

Superficial mycoses (tineas)

• Mostly occur in the tropics

• Restricted to the outer surface of the hair and skin

Piedraia hortae

A filamentous member of the Ascomycota which causes black piedra, a disease of the hair shaft characterized by brown/black nodules on the scalp hair.

Trichosporon cutaneum

A yeast belonging to the Basidiomycota that is common in soil, water, plants, mammals, and birds, as well as being a member of the normal flora of the mouth, skin, and nails. It causes white piedra, a superficial infections of the skin, scalp, and pubic hair.

Cutaneous mycoses

Fungi that commonly cause disease in the non-living tissues of skin, hair, or nails/claws of people and animals, by growing in a zone just above where the protein keratin is deposited.

Microsporum, Trichophyton, Epidermophyton

• Three genera of cutaneous mycoses

• Degrade keratin and grow as non-invasive saprotrophs on skin and its appendages, but their growth causes irritation and inflammation of underlying epithelial cells, this being an allergic reaction that may result in death of these cells.

Subcutaneous mycoses

• Generally caused by fungi that are normally saprotrophic inhabitants of soil, particularly in tropical and subtropical areas of Africa, India, and South America

• Become infective by being introduced through wounds in the skin

• Most infections involve people who normally walk barefoot.

Madurella mycetomatis and M. grisea

These cause human mycetoma (madura foot), which is a localized infection causing locally invasive tumor-like abscesses, accompanied by chronic inflammation, resulting in swelling, distortion, and ulceration of the infected body part. The fungus is introduced through mild wounds in the skin and may grow for several years in the cutaneous and subcutaneous tissues, extending to connective tissues and bones. Mycetomas are usually resistant to chemotherapy, leaving surgery, even amputation, as the only resolution.

Sporothrix schenckii

• Causes sporotrichosis

• The fungus occurs in soil worldwide although the disease is localized, also called “rose handler’s disease,” sporotrichosis starts by entry of the fungus through minor skin injury and can then spread through the lymphatic system. As the yeast form is distributed by the lymphatic system, disseminated sporotrichosis can result in infections of the lungs and bones and joints, endophthalmitis (inflammation of the internal layers of the eye), meningities, and invasive sinusitis.

Systemic mycoses

• Infections that affect the whole body

• Divided to primary virulent pathogens and opportunistic pathogens

Primary virulent pathogens

• Can establish infections in normal hosts

• Usually gain access to the host via the respiratory tract

Opportunistic fungi

• Cause disease in individuals with compromised host defense mechanism

• Causes deep mycosis and invades via the respiratory tract, alimentary tract, or intravascular devices

Ustilago maydis

A maize pathogen under the phylum Basidiomycota

Cryptococcus neoformans

A human pathogen under the phylum Basidiomycota that causes respiratory illnesses and meningitis

Amanita

A poisonous mushroom under the phylum Basidiomycota

Aspergillus niger

An imperfect fungus under the phylum Deuteromycota and is commonly found as a food contaminant

Ergotamine

This is a major mycotoxin produced by the Claviceps species, which if ingested can cause gangrene, convulsions, and hallucinations

Lobaria pulmonaria

This lichen is a symbiosis of fungal, algal, and cyanobacterial species. The functions of both symbiotic organisms are so closely intertwined that they function almost as a single organism.

Myxomycetes

Other term for slime molds

Oomycetes

• Other term for water molds

• Resemble other fungi because they have branched filaments and form spores

• Have cellulose in their cell walls, while other fungi have chitin

• Have a complex reproductive cycle which includes flagella-bearing zoospores

• Parasites of fish and cause disease in plants such as tobacco, grapes, and potatoes

Ophiostoma ulmi and Ophiostoma novoulmi

• These tree pathogens can cause Dutch elm disease

• These fungi spread within stems and roots of living elms both by passive transport of spores and by mycelial growth of colonies initiated by spores that germinate in the xylem

Cryphonectria parasitica

• Fungus that invades the tree through wounds of cracks in the chestnut’s tree’s bark

• Infected saplings will dies within a year, but large mature trees can take several years to succumb to the disease

• Host: American chestnut (Castanea dentata), European chestnut (C. sativa), Chinese chestnut (C. mollissima)

Pityriasis versicolor

• Superficial mycoses

• Liphophilic fungi

• Found in areas of the body rich in sebaceous gland

• Lesions are described as scales, giving a dry chalky appearance

• Etiologic agent: Malassezia furfur

Tinea nigra

• Found on palmar and plantar areas of the stratum corneum

• Lesions are described as light to blackish macular areas

• Etiologic agent: Exiophiala werneckii (a dermataceous fungi producing melanin)

T. mentagrophytes

Trichophyton with grape-like clusters on terminal branch

T. rubrum

Trichophyton with teardrop-shaped microconidia

T. schoenleinii

Trichophyton that leads to the formation of scutula (crusts) around the follicle

M. canis

Microsporum with macroconidia that have curved or hooked spiny tips

M. gypseum

Microsporum that have thinner-walled macroconidia

M. audouinii

Microsporum that have thick-walled chlamydospores

Aspergillus spp.

• Aspergillosis

• Usually occurs in people with lung disease or weakened immune systems

• Primarily affects the lungs and include allergic reactions and infections in other organs

Candida

• Candidiasis

• Infections result in minimal complications such as redness, itching, and discomfort, though complications may be severe or even fatal if left untreated in certain populations

• Commonly involving the skin, oral mucosa (thrush), respiratory tract, or vagina; occasionally there is a systemic (blood) infection or endocarditis

Histoplasma

• Histoplasmosis

• The fungus lives in the environment, particularly in soil that contains large amounts of bird or bat droppings

• People can get histoplasmosis after breathing in the microsporic fungal spores from the air