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Biol 3400 Tortora et al., Chapter 12

The

I. The Fungi = the study of fungi: Myco is Greek for “fungi”, ology = “the study of”

A. What are fungi? • Primarily terrestrial • 100,000 have been described (Estimates suggest that there are up to 1.5 x 106 species) • Fungi can represent up to 50% of the in agricultural soils and 90% of the biomass in soils • Diverse group of organisms • Essential to on • Fungi are the Primary !! Without fungi there would be an excess of biomass • Nearly all depend on symbiotic fungi – mycorrhizae. These fungi aid the plants in absorbing water and from soil • Major cause of – plants are particularly vulnerable • Important for a number of industrial involving – , , but also , . Also used in organic acid production () and (). cerevisiae is the best understood .

B. Characteristics of fungi 1. They are eukaryotes and contain: • a nucleus containing • membrane bound (mitochondria, ER, golgi, , …)

2. Fungi are nonvascular

3. Fungi reproduce by • Spores are important for several reasons, including surviving environmental stress (, limitation) and dissemination (i.e., mass multiplication or r – strategy). • Spores are typically not motile • Both sexual and asexual spores are produced, depends on the and conditions • There are several types of sexual spores that tend to be specific to fungal subdivisions. The sexual spores tend to result from the fusion of that may come from the same (i.e., self fertilizing or homothallic species) or from different but sexually compatible mycelia (i.e., heterothallic species)

• There are several types of asexual spores o Sporangiospores – spores that form within a sac () at the hyphal tip o Conidiospores – spores are not produced in a sac but rather at the tip or on the sides of the hyphae o Blastospores – a vegetative mother produces these spores by o Arthrospores – fragments to form cells that behave like spores o – cells surrounded by a thick wall before separation

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4. Fungal vegetative cells may be unicellular () or comprised of a thread-like structure called a thallus → the vegetative structure from which they get nutrients

5. Fungi have -developed cell walls comprised mainly of (N-acetylglucosamine)

6. All fungi are chemoorganotrophs (heterotophic: must feed on preexisting organic )

7. Fungi utilize extracellular (“digest then ingest”)

8. Most fungi store their as (similar to ), plants use starch and oils as compounds

9. Fungal membranes possess a unique called (replaces cholesterol found in membranes)

10. Fungi have a unique lysine pathway

11. Fungal are unique

12. Most fungi have relatively small with minimal repetitive DNA • is generally accomplished without dissolution of the

C. The Fungal Thallus • Vegetative structure • plural - thalli

• composed of hypha (pl. hyphae): releases that breakdown food around it, the fungus then absorbs the resulting products of hydrolysis o Thread-like structure o of terrestrial existence (allowed fungi to grow on land)

• = multiple hyphae. This is a collective term. The extensive -like system found underground for many fungi and accounts for the bulk of the fungal biomass.

• Hypha may have cross walls or septa (sing. = septum). In some species the hyphae are aseptate (ceonocytic)

• Cell = single celled thallus (an to an aquatic environment) o Yeasts reproduce asexually via budding. This is a good characteristic for distinguishing between and yeasts o Some fungi are dimorphic and can change from a yeast form (Y) to a mycelial

form (M) in response to environmental factors such as (nutrients, CO2 tension, temperature,…). This shift is called the YM shift.

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D. How do fungi grow? • Fungal growth occurs always at the tips of hypha. The stays stationary and hyphae grow out from it.

E. Classification of fungi: • Originally fungi were grouped based on phenetic characteristics that did not represent their natural grouping • Molecular have revolutionized how we look at the fungi

The Fungi includes eight subdivisions: o o o o o Urediniomycetes o o o

• The first four subdivisions have distinct sexual spores and associated structures that can be used to identify the . They also often produce asexual spores that are responsible for the success of the organism.

1. “Chytrids” • The chytrids produce motile spores = • Zoospores are typically uniflagellate • Flagella are whiplash type and are attached posteriorly • Zoospores are typically formed in specialized structures = zoosporangia ( sacs) • Zoosporangium holds thousands of the actual zoospores. • Cell walls composed of rather than chitin

Ecological niches: • Decomposers in aquatic • in aquatic ecosystems (e.g., decline caused by ”disease caused by chytrids”) • Mutualistic symbiotic relationships with animals o (such as cattle) o Intestines of hind-gut fermenting animals such as horses

• e.g.,

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2. Zygomycota ”Zygosporic fungi” • Produce sexual spores called in a zygosporangium • “zygos” = yoke and “spora” = seed • Zygospores are typically thick walled and pigmented = a survival structure resistant to UV light and microbial factors • This group of fungi also typically produces non-motile asexual spores called sporangiospores • Asexual spores are often formed in specialized structures called a sporangium (spore sac; sporangia = pl.) • Thousand of spores are produced → contribute to the success of fungi. • The sporangia are produced on tall stalks in to introduce the spores to more turbulent patterns above the boundary layer. This ensures better wind dispersion. • Coenocytic hyphae

Ecological niches: • Decomposers in the soil - decaying and animal matter in the soil • A few are parasites of plants, , other animals and

• e.g., ,

3. Ascomycota ”Sac Fungi” • A very large group of fungi that produce sexual spores = • These are typically formed in “sac-like” structures termed asci (singular = ) • Ascospores are typically forcibly discharged (via pressure, such as being stepped on) • Asci are borne “naked” or in specialized fruiting structures called ascomata (or )

• Ascomata are often formed in “stroma”→ hyphae produced by a fungus organize into an interwoven

• Many Ascomycetes fungi are yeast

Asexual • Many members of the ascomycota also reproduce asexual spores are termed conidiospores or “conidia” • This is an ecological adaptation that allow fungi to access and exploit new niches

• Fungi as a rule are good examples of r-selection reproductive strategies: o Small size o Many offspring o Reduced o Early maturity o Most individuals die within a short period of

• There is tremendous diversity in asexual spores and the way they are formed • This is such a successful strategy, that some fungi have even lost the ability to reproduce asexually

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Ecological niches: • Important decomposers in freshwater, marine and terrestrial habitats because they degrade many recalcitrant materials, including cellulose, lignin and collagen • Many are parasites on higher plants - cause important plant such as powdery and Dutch disease • Many are edible – morels and

• e.g., , ,

4. Basidiomycota “Basidiosporic fungi” • Commonly known as the club fungi, contains the , , bracket fungi, rusts and smuts • Have gills (underside of cap) that maximize surface area • Produce on specialized structures called . May be held in fruiting bodies known as

Ecological niches: • Important terrestrial decomposers that decompose plant material (cellulose and lignin) • Many mushrooms are cultivated for food – • Some mushrooms produce specific secondary metabolites – that are either poisonous ( phalloides – death angel) or hallucinogenic

• e.g., Agaricus, Amanita

5. Urediniomycetes and Ustilaginomycetes • Often considered as Basidiomycota but they do not produce large basidiocarps but rather produce small basidia that arise at the tip of the hyphae at the surface of the plant

Ecological niches: • Important plant pathogens causing and • Some Urediniomycetes cause disease in humans

• e.g.,

6. Glomeromycota • Often considered as zygomycetes by some • Only is known to occur in this group – spores are produced and germinate when in contact with of a suitable host plant

Ecological niches: • Important plant symbionts – most are endomycorrhizal symbionts of vascular plants. The fungus helps protect the host plant from stress and delivers soil nutrients to the plant which in turn provides to the fungus

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7. Microsporidia • Used to considered as ; however, molecular analysis of rRNA and α and β-tubulin show that this group is most closely related to fungi • Unlike other fungi, this group lacks mitochondria, and • Small spores are produced and these are viable outside the host

Ecological niches: • Obligate intracellular parasites that infect insects, fish, and humans

• e.g., Encephalitozoon

Fungal Classification

The Eukaryote Kingdoms: • Plantae • Animalia • Protista • Fungi

Domain = Eukarya = Fungi = -mycota = -mycetes Order = -ales Family = -aceae = ------Species = ------

II. The • Relatively simple eukaryotic photoautotrophs • Mostly found in aquatic environments but some are found in most soils or on trees is sufficient moisture is available • Identification of unicellular or filamentous algae requires microscopy • It is estimated that 80% of the earth’s is produced by planktonic algae

A. Structure • Unicellular or multicellular • Body of a multicellular alga is called a thallus. The thalli of consist of branched holdfasts (anchor the alga to the i.e., a rock), stem-like stipes and leaf-like blades. The cells covering the thallus can carry out . No conductive or vascular tissues are found in algae and they absorb nutrients from the water over their entire surfaces.

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B. Life • All algae can reproduce asexually (i.e., fragments of a or filamentous algae can form a new thallus or filament, respectively). Unicellular algae divide by mitosis followed by to produce two new daughter cells • occurs in algae. This process may alternate with asexual reproduction

C. Nutrition • Most algae are photoautotrophs but one group of fungal like algae (Oomycota) are chemoheterotrophs

D. Algal • Algae are classified according to their rRNA sequences, structures, and cellular arrangements (multicellular vs unicellular) • Refer to Table 12.4 for some of the characteristics of select groups of algae. Review the description of members of these groups in textbook and prepare your own notes.

III. The • Unicellular, chemoheterotrophic eukaryotes found in kingdom protista • Represent a “mixed bag” of organisms that some claim contains more diversity than all other eukaryote groups combined • The feeding and growing stage is known as the trophozoite. This stage tends to feed on bacteria and small particulate nutrients

A. Life cycle • Protozoa reproduce asexually by , budding or schizogony. Schizogony is multiple fission: the nucleus undergoes several rounds of divisions before the cell divides. After many nuclei are formed, a portion of concentrates around each nucleus prior to the cell separating into daughter cells • Sexual reproduction has been observed in some protozoa • Some protozoa will produce protective during adverse conditions permitting the organisms to survive when i) nutrients, water or oxygen are lacking, ii) temperatures are unsuitable, or iii) toxic chemicals are present

B. Nutrition • Protozoa are mostly aerobic . Some intestinal protozoa are capable of anaerobic growth. There are two groups of protozoa contain : and euglenoids. • All protozoa live in areas with a large supply of water. Some absorb nutrients across the plasma membrane. Others have a strong protective covering under the plasma membrane known as the pellicle and require specialized structure to take in nutrients. Similarly others engulf food by (e.g., ) or have a mouthlike opening called a that is used to collect food . Digestion occurs in membrane enclosed vacuoles in all protozoa.

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C. Protozoal Taxonomy • This is a large and diverse group of organisms. Classification into a number of phyla is based upon rRNA gene as well as morphological characteristics • Microspora are no longer considered protozoans. Molecular methods have determined these organisms to be fungi

1. Archaezoa • Lack mitochondria but have a unique (i.e., ) that appears to be a remnant of the mitochondria. • Many live a symbionts in the digestive tracts of animals • Typically spindle shaped with flagella projecting from one end

e.g., vaginalis lamblia forms cysts in feces that persist in the environment

2. • Move by • Lack cell walls

e.g., histolytica – causes amoebic dysentry

3. • Nonmotile in mature forms • Obligate intracellular parasites • Characterized by the presence of a complex of special organs at the cell apex • Usually have complex life cycles involving transmission between several hosts

e.g., – causes malaria

4. Ciliophora • Cells are covered with cilia that are arranged in precise rows. The cilia are used for locomotion as well as to propel food into the cytostome

5. • Two groups of flagellated cells are included in this group o Euglenoids – photoautotrophs with a at the anterior end. The membrane is a semi-rigid pellicle e.g., o Hemoflagellates – blood parasites transmitted by blood feeding insects e.g., brucei causes African sleeping sickness

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