Lecture 6 PHM2111

Growth requirements of fungi

A. Nutritional Requirements B. Environmental requirements

Nutritional Requirements of fungi

All fungi are Chemoheterotrophs: § They may be: A. Saprophytic (soprobes) B. Parasitic (parasites)

Fungi cell membrane

Contains sterols called Ergosterols.

Most fungi are Saprophytic or parasitic?

Saprophytic

Hyphae

The branching, threadlike tubes that make up the bodies of multicellular fungi Molds are filamentous fungi that consist of masses of intertwined filaments called "hyphae" (sing., hypha).

Fungi reproduce sexually by

Through production of sexual spores.

pseudohypha

chain of yeasts formed when buds remain attached in a row

Mycelium

mass of hyphae Hyphae typically grow together across and above a surface to form a compact, macroscopically visible tuft

Aseptate hyphae

no cross walls Also called: (coenocytic hyphae) § (coeno- = "common"; -cytic = "cell") §The cytoplasm within the hypha is not divided into cells; no septa.

mycologist

scientist who studies fungi

Yeasts

unicellular fungi

Chlamydiospores

(chlamys, cloak or outer coat). § A spherical spore formed by the thickening of a hyphal cell. § It is released when the surrounding hypha fractures, and it serves as a survival or resting cell

Fungi reproduce by asexual means in one of four ways

1. Fragmentation (molds only): Mycelial fragmentation occurs when a fungal mycelium separates into pieces with each component growing into a separate mycelium. 2. Budding (yeasts only): It grows swellings on its surface called buds, that become separate cells. 3. Binary fission (yeasts only) 4. Asexual spores.

Functions of fungal spores include:

1. Multiplication 2. Survival: Because they are resistant to heat, cold, acids, bases, and other chemicals. 3. Genetic variation: (sexual spores) 4. Dissemination: Because of their relatively light weight, spores are dispersed widely through the environment by air, water, and living things. Upon encountering a favorable substrate, a spore will germinate and produce a new fungus colony in a very short time.

Environmental Requirements of fungi

1. Oxygen § The majority of fungi are aerobic organisms, except the facultative yeasts, which can grow in either the presence or absence of oxygen. 2. Temperature § Most fungi grow best at about 23°C, a temperature close to normal room temperature. § Exceptions are the pathogenic fungi, which grow optimally at 37°C, which is body temperature. § Dimorphic fungi grow as yeast-like cells at 37°C and a mycelium at 23°C. 3. pH § Most fungi grow under mildly acidic conditions at a pH between 5 and 6. 4. High sugar concentration enhances fungal growth, and laboratory media for fungi usually contain extra glucose; example: Sabouraud dextrose (glucose) agar.

Types of asexual spores:

1. Sporangiospores 2. Conidiospores 3. Arthrospores 4. Chlamydospores 5. Blastospores

Although there are many variations in fungal sexual reproduction, all include the following three stages.

A. Plasmogamy B. Karyogamy C. Meiosis § The diploid nucleus gives rise to haploid nuclei (sexual spores) by meiotic division. § A visible fruiting body often results during sexual reproduction and it is the location of the haploid spores. The most recognized fruiting body is the mushroom

Based on molds structures, hyphae can be classified into

A. Septate hyphae B. Aseptate hyphae

Classification of fungi is based on

A. The presence or absence of sexual reproductive cycle B. The nature of the sexual spores

Based on molds functions, hyphae can be classified into

A. Vegetative hyphae B. Aerial hyphae

Chemoheterotrophs

An organism that must consume organic molecules for both energy and carbon. They absorb preformed organic matter.

multinucleated cytoplasm is in which of the following? Aseptate hyphae Septate hyphae

Aseptate hyphae

Fungal Spores

Fungal spores are very resistant structures that are carried great distances by wind. They are resistant to heat, cold, acids, bases, and other chemicals (Note: Bacterial spores are more resistant non reproductive structures). § Many people are allergic to fungal spores. § Fungal spores are used in the identification of fungal

saprophytic fungi

Fungi that get their energy from decaying organic matter Together with many bacterial species, these fungi make up the decomposers that recycle organic matter. § In industrial settings, these decompositions can be profitable. The fungus Trichoderma, for example, produces enzymes to degrade cellulose and give jeans a "stone-washed" appearance.

Karyogamy

Fusion of two haploid nuclei to form a diploid nucleus. Occurs in many fungi, and in animals and plants during fertilization of gametes (means union of nuclei) § The (+) and (−) haploid (1n) nuclei fuse to form a diploid zygote nucleus (2n).

Aerial hyphae

Hyphae of a fungus that grow above the substrate § Reproductive, or fertile, hyphae that branch off vegetative mycelia above the surface upon which the fungus grows. § Function: § They are responsible for the production of fungal reproductive bodies called "spores".

The taxonomic classification of fungi changes periodically. § One current classification divides the Kingdom Fungi into five phyla:

I. Deuteromycota II. Chytridiomycota III. Zygomycota IV. Ascomycota V. Basidiomycota

Yeasts Culture

In the laboratory, yeasts produce colonies that are quite similar in appearance to bacterial colonies (smooth creamy colonies).

Fungi can be classified into

Macroscopic Fungi Microscopic fungi

Asexual spores

Produced via mitosis and cell division; formed by the hyphae of one organism The products of mitotic division of a single parent cell. They are reproductive structures which are produced by one parent only (through mitosis) and are genetically identical to that parent. § They are haploid cells (1n). § They are formed on the ends of aerial hyphae. § In laboratory settings, most fungi exhibit only asexual spores. Consequently, clinical identification is based on microscopic examination of asexual spores.

Are all fungi detrimental (bad) for other organisms?

Some are harmful, whereas others are beneficial

Reproduction by budding in yeasts

Sometimes a string of elongated attached buds is formed; this string of elongated buds is called a pseudohypha (pl., pseudohyphae). It resembles a hypha, but because of its manner of formation, it is not a true hypha like that of molds.

Types of fungal Spores

There are two types of fungal spores: A) Asexual spores B) Sexual spores

In which domain is fungi?

They are classified in a separate kingdom within the domain "Eukarya"

yeasts shape

They can be spherical, oval, or elongated.

Microscopic fungi

They can only be seen by microscope. §They include: 1. Yeasts 2. Molds 3. Dimorphic fungi

Do fungi have Organelles?

They have organelles (mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus and a cytoskeleton)

Yeasts Reproduction

They reproduce by asexual reproduction through one of two processes: A. Budding: It grows swellings on its surface called buds, that become separate cells. B. Binary fission

Fungi

a diverse group of eukaryotic organisms.

parasitic fungi

absorb nutrients from the cells of living hosts They live on plants or animals often causing disease. § Most such fungi are opportunistic and only cause serious disease in immunocompromised individuals.

Sexual spores

are formed through a process involving the fusing of two parental nuclei followed by meiosis. § Some species of fungi produce both asexual and sexual spores. Spores that are formed through a process involving the fusion of two parental nuclei (of opposite mating types) followed by meiosis. § Many fungi reproduce both sexually and asexually, but a few have only asexual reproduction.

Septate hyphae

hyphae with cross walls §The cytoplasm within the hypha is divided into cells by cross-walls or septa (sing., septum).

Molds

multicellular fungi

Macroscopic Fungi

mushrooms, puffballs, gill fungi They can be seen by naked eye.

Fungi can reproduce...........

sexually or asexually

mycology

study of fungi

septa

the cells that make up hyphae are divided by these cross sections §The septa often has either a single pore or multiple pores that enable free passage of cytoplasm.

Plasmogamy

the union of the cytoplasms of two parent mycelia (means union of cytoplasm) § A haploid nucleus of a donor cell (+) penetrates the cytoplasm of a recipient cell (−) leading to a dikaryotic (di = "two"; karyo = "nucleus") stage where two haploid nuclei coexist in a single cell.

Arthtrospores

§ (Arthtron = "joint") § Rectangular spores formed when a septate hypha fragments through splitting of the cell walls or septa.

Conidiospores (conidia)

§ (sing., conidium; conidio = "dust"). § The most common asexual spores. § They are unprotected free spores not enclosed by a spore-bearing sac. § They are formed on supportive structures called conidiophores.

Absorption of nutrients

§ Fungi secrete enzymes into the surrounding environment that break down (hydrolyze) complex organic compounds into simpler ones. As a result of this extracellular digestion, simpler compounds, like glucose and amino acids, can be absorbed. § Fungi have enzymes for digesting an incredible array of substances, including feathers, hair, cellulose, petroleum products, wood, even rubber. § The mycelium formed by a mold represents the "feeding network" for these fungi. The filamentous nature of hyphae results in a large surface area relative to the volume of cytoplasm which allows adequate nutrient absorption. § For the yeasts, nutrients are absorbed across the cell surface, similar to the way bacterial cells obtain their nutrients.

Fungi cell wall

§ It is composed of large amounts of chitin. § Chitin is a carbohydrate polymer of acetylglucosamine units; that is, glucose molecules containing amino and acetyl groups.

Commercial and medical importance of fungi

§ Naturally occurring yeasts on the skin of grapes and other fruits and grains are responsible for fermentation processes that takes place during production of wine and beer. § The common yeast Saccharomyces cerevisiae ("baker's yeast") is used for bread production. § Yeasts are also a good source of nutrients for humans because they produce many vitamins and proteins. § Antibiotic production, such as Penicillin. § Some molds are used to produce large quantities of enzymes (such as amylase, which converts starch to glucose), citric acid, and other organic acids that are used commercially. § The flavor of cheeses such as bleu cheese and Roquefort is the result of molds that grow in them. § Some yeasts (e.g., Candida albicans and Cryptococcus neoformans) are human pathogens

Sporangiospores

§ Spores develop within sacs or vessels called sporangia (sing., sporangium; angio = "vessel") which is attached to a stalk "the sporangiophore". § They are initially enclosed but are released when the sporangium ruptures.

Dimorphic fungi

§ They are capable of growing either as yeast-like cells or as mycelia, depending on the environmental conditions.

Blastospores

§ They are produced by budding from a vegetative mother cell that is a yeast or another spore; also called "a bud

Vegetative hyphae

§ They grow flat along surfaces upon which the fungus grows. § Function: § They penetrate growth surfaces to digest and absorb nutrients

Many of the fungi that cause disease in humans are dimorphic:

§ They grow in the soil as molds (at 25-30°C). § When their spores, carried by air, are introduced into the warm, moist environment of the human body (at 35-37°C), they develop into the yeast form of the organism and cause disease.

Fungi nucleus

§ They have one or more nuclei. § The DNA in the nucleus is wrapped around histone proteins § Yeast cells often contain plasmids

During sexual reproduction two mating types (+/-) are produced:

§ When both mating types are present in the same mycelium, it is called "Homothallic, or selffertile mycelium". § When only one mating type is present in a mycelium, it is called "Heterothallic mycelium". Heterothallic mycelia require two different, but compatible, mycelia to reproduce sexually

Genetic variation due to sexual spores formation:

§ When fungi of different genetic makeup combine their genetic material. § A union of genes from two parents creates offspring with combinations of genes different from that of either parent. § The offspring from such a union can have slight variations in form and function that are potentially advantageous to the adaptation and evolution of their species.