CHAPTER 13 - DIVERSITY OF EUKARYOTIC MICROBES AND THE PARASITIC HELMINTHS

FUNGI

• They are chemoheterotrophs and acquire food by absorption.

• are multicellular.

• Most reproduce with sexual and asexual spores.

cellulases

Fungi uses extracellular enzymes to digest the hard parts of plants

mycorrhizae

fungi which help plant roots absorb minerals and water from the soil

chemoheterotrophs

fungi are — requiring organic compounds for energy and carbon

aerobic or facultatively anaerobic

Fungi can be —

Fungi-farming ants

- leaf-cutter ants are in obligate symbiotic relationship with Lepiotaceae fungus

Mycology

study of fungi

vegetative structures

in fungi, are composed of the cells involved in catabolism and growth.

1. Molds and fleshy fungi

2. Yeasts

3. Dimorphic fungi

Vegetative Structures of Fungi

Molds and fleshy fungi

• vegetative hyphae

• reproductive or aerial hyphae

thallus

of a mold or fleshy fungus consists of long filaments of cells joined together;

hyphae

filaments in thallus

septa

In most molds, the hyphae contain cross-walls called —

• divide them into distinct, uninucleate (one-nucleus) cell-like units.

septate hyphae

hyphae that contain cross-walls called septa (singular: septum), which divide them into distinct, uninucleate (one-nucleus) cell-like units.

coenocytic hyphae

few classes of fungi, the hyphae contain no septa and appear as long, continuous cells with many nuclei.

vegetative hypha

The portion of a hypha that obtains nutrients

reproductive or aerial hypha

the portion concerned with reproduction

mycelium

the hyphae grow to form a filamentous mass called a

Yeasts

• are nonfilamentous, unicellular fungi that are typically spherical or oval

• budding yeasts

• fission yeasts,

Budding yeasts

• Saccharomyces

• divide unevenly

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One yeast cell can in time produce up to — daughter cells by budding

pseudohypha

Some yeasts produce buds that fail to detach themselves; these buds form a short chain of cells called

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.

Candida albicans

attaches to human epithelial cells as a yeast but usually requires pseudohyphae to invade deeper tissues

Fission yeast

• Schizosaccharomyces

• divide evenly to produce two new cells.

Fission

, the parent cell elongates, its nucleus divides, and two offspring cells are produced.

facultative anaerobic

Yeasts are capable of — growth, which allows these fungi to survive in various environments.

Saccharomyces

species produce ethanol in brewed beverages and carbon dioxide for leavening bread dough.

Dimorphic Fungi

Some fungi, most notably the pathogenic species, exhibit dimorphism—two forms of growth

mold or yeast

Dimorphic Fungi can either grow as

moldlike forns

produce vegetative and aerial hyphae;

yeastlike forms

reproduce by budding

37°C; 25°C

Dimorphism in pathogenic fungi is temperature-dependent: at —, the fungus is yeastlike, and at —, it is moldlike.

fragmentation

Filamentous fungi can reproduce asexually by

spores

both sexual and asexual reproduction in fungi occurs by the formation of—

• detaches from the parent and germinates into a new mold

asexual or sexual

. Fungal spores can be either —

Asexual spores

are formed by the hyphae of one organism

• When these spores germinate, they become organisms that are genetically identical to the parent.

• are produced by an individual fungus through mitosis and subsequent cell division;

• there is no fusion of the nuclei of cells

Sexual spores

• result from the fusion of nuclei from two opposite mating strains of the same species of fungus.

• require two different mating strains and so are made less frequently than asexual spores.

conidiospore and sporangiospore

Two types of asexual spores

conidiospore

a unicellular or multicellular spore that is not enclosed in a sac

Penicillium and Aspergillus

Conidiospores are produced by

arthroconidia

• Conidia formed by the fragmentation of a septate hypha into single, slightly thickened cells

• Coccidioides immitis

blastoconidia

• conidia that are formed from the buds of its parent cell

• Candida albicans and Cryptococcus

chlamydoconidium

• conidiospore is a thick-walled spore formed by rounding and enlargement within a hyphal segment

• Candida albicans

sporangiospore

formed within a sporangium, or sac, at the end of an aerial hypha called a sporangiophore

1. Plasmogamy

2. Karyogamy

3. Meiosis

A fungal sexual spore results from sexual reproduction, which consists of three phases:

Plasmogamy

A haploid nucleus of a donor cell (+) penetrates the cytoplasm of a recipient cell (-).

Karyogamy.

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.

• Fungi usually grow better in an environment with a pH of about 5, a.

• Almost all molds are aerobic. Most yeasts are facultative anaerobes.

• Most fungi are more resistant to osmotic pressure than bacteria;

• Fungi can grow on substances with a very low moisture content,

• Fungi require somewhat less nitrogen than bacteria for an equivalent amount of growth.

• Fungi are often capable of metabolizing complex carbohydrates, such as lignin

fungi differ from bacteria in certain environmental requirements and in the following nutritional characteristics:

• Zygomycota

• Microsporidia

• Ascomycota

• Basidiomycota

Medically Important Fungi

Zygomycota

• conjugation fungi, are saprophytic molds that have coenocytic hyphae.

• example is Rhizopus stolonifer

zygospore

• sexual spore of zygomycota

• is a large spore enclosed in a thick wall

• forms when the nuclei of two cells that are morphologically similar to each other fuse.

Microsporidia

• are unusual eukaryotes because they lack mitochondria.

• don’t have microtubules, and they’re obligate intracellular parasites.

Ascomycota

or sac fungi, include molds with septate hyphae and some yeasts.

conidia

asexual spores of ascomycota

• means dust, and these spores freely detach from the chain at the slightest disturbance and float in the air like dust.

ascospore

• forms when the nuclei of two cells that can be either morphologically similar or dissimilar fuse.

• These spores are produced in a saclike structure called an ascus

Basidiomycota

or club fungi, also possess septate hyphae.

• This phylum includes fungi that produce mushrooms.

Basidiospores

formed externally on a base pedestal called a basidium

teleomorphs

fungi that produce both sexual and asexual spores.

anamorphs

Some ascomycetes have lost the ability to reproduce sexually

• ex. Penicillium

Deuteromycota

fungi whose sexual cycle had not been observed were put in a “holding category

mycosis

fungal infection is called a

systemic, subcutaneous, cutaneous, superficial, or opportunistic

Mycoses are classified into five groups according to the degree of tissue involvement and mode of entry into the host

Systemic mycoses

are fungal infections deep within the body

• mycoses are usually caused by fungi that live in the soil.

• Two systemic mycoses, histoplasmosis and coccidioidomycosis

• route of transmission is inhalation of spores

Coccidioidomycosis

• caused by Coccidioides immitis

• a form of pneumonia that is most commonly found in AIDS patients

• generally can be found in the lungs of a healthy individual without causing infection

Subcutaneous mycoses

are fungal infections beneath the skin caused by saprophytic fungi that live in soil and on vegetation.

• route of transmission is direct implantation of spores into puncture wound in the skin

Sporotrichosis caused by Sporothrix schenckii

ex. of subcutaneous mycosis

dermatophytes

• Fungi that infect only the epidermis, hair, and nails

cutaneous mycoses

infections of Fungi that infect only the epidermis, hair, and nails ( dermatophytes)

• human to human, animal to human, or direct contact with infected hair and epidermal cells

avoid contact, keep susceptible skin areas dry

• Try to remove shoes when possible to dry out feet.

• Avoid touching places such as locker room floors or other public places with bare feet.

• Never borrow other people’s shoes.

• have pets checked if areas of hair loss are seen.

prevention of cutaneous mycosis

keratinase

Dermatophytes secrete -, an enzyme that degrades keratin, a protein found in hair, skin, and nails.

superficial mycoses

are localized along hair shafts and in superficial (surface) epidermal cells. These infections are prevalent in tropical climates.

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.

pneumatocystis, stachybotrys, mucormycosis, aspergillosis, cryptococcosis, yeast infection

examples of opportunistic mycoses

Pneumocystis

is an opportunistic pathogen in individuals with compromised immune systems and is the most common life-threatening infection in AIDS patients

Stachybotrys

Another example of an opportunistic pathogen is the fungus Stachybotrys which normally grows on cellulose found in dead plants but in recent years has been found growing on water-damaged walls of homes.

Mucormycosis

is an opportunistic mycosis caused by Rhizopus and Mucor (MU- -kor); the infection occurs mostly in patients who have diabetes mellitus, have leukemia, or are undergoing treatment with immunosuppressive drugs.

Yeast infection

or candidiasis, is most frequently caused by Candida albicans and may occur as vulvovaginal candidiasis or thrush, a mucocutaneous candidiasis.

Thrush:

common infection of the mouth in infants and toddlers or other immuno - compromised individuals

Aspergillus niger, Saccharomyces cerevisiae, Trichoderma, Taxomyces, Entomophaga, Coniothyrium, Paecilomyces fumosoroseus

ECONOMIC EFFECTS OF FUNGI

Aspergillus niger

has been used to produce citric acid for foods and beverages since 1914

Trichoderma

is used commercially to produce the enzyme cellulase, which is used to remove plant cell walls to produce a clear fruit juice

Coniothyrium minitans and Paecilomyces fumosoroseus

Scientists are investigating the use of several fungi to kill pests:

Coniothyrium minitans

feeds on fungi that destroy soybeans and other bean crops.

Paecilomyces fumosoroseus

is being used as a biological alternative to chemicals to kill termites hiding inside tree trunks and other hard-to-reach places.

Cryphonectria parasitica

an ascomycete that causes fungal blight that killed chestnut trees in the U.S.

Ceratocystis ulmi

causes Dutch elm disease, carried from tree to tree by a bark beetle; the fungus blocks the afflicted tree’s circulation

lichen

• is a combination of a green alga (or a cyanobacterium) and a fungus

• are placed in the Kingdom Fungi most often an ascomycete.

• often the pioneer species in newly exposed soil or rock

• secrete organic acids that chemically weather rock

• accumulate nutrients needed for plant growth

Crustose lichens, foliose lichens, fruticose lichens

Lichens can be grouped into three morphologic categories

Crustose lichens

likens that grow flush or encrusted onto the substratum

foliose lichens

lichens that are leaflike

fruticose lichens

lichens that have fingerlike projections

medulla

The lichen’s thallus, or body, forms when fungal hyphae grow around algal cells to become the

rhizines, or holdfasts

Fungal hyphae project below the lichen body to form —

cortex

Fungal hyphae also form a —, or protective covering, over the algal layer and sometimes under it as well.

erythrolitmin

the dye used in litmus paper is extracted from a variety of lichens

dermatitis

some lichens or their acids can cause allergic contact — in humans

bioindicators

lichens can be used as — of air pollution