Fungi: Anatomy, Reproduction & Role

• Fungi, lichens, algae, protozoa, and slime molds are diverse eukaryotic organisms with unique characteristics and roles.
• Helminths are also a significant group of organisms studied alongside these microbes.

Fungi Functional Anatomy & Reproduction

• Fungi are chemoheterotrophs that obtain food through absorption.
• Most fungi are multicellular, except for yeasts.
• Fungi reproduce using sexual and asexual spores.
• Fungi include molds, fleshy fungi (mushrooms), and yeasts.
• They can be aerobic, facultatively anaerobic, or, rarely, anaerobic.
• Fungi may be unicellular or multicellular organisms.
• Mycology is the study of fungi.
• Only about 200 of the more than 100,000 species of fungi are pathogenic to humans and animals.
• Fungal diseases are a significant healthcare concern, especially for immunocompromised individuals, and their incidence has increased since the 2000s.
• Fungi decompose dead plant matter, recycling vital elements in the food chain using extracellular enzymes like cellulases.
• Mycorrhizae are symbiotic fungi that help plant roots absorb minerals and water from the soil.
• Fungal colonies are vegetative structures involved in catabolism and growth.

Molds & Mushrooms (Fleshy Fungi)

• The thallus (body) of a mold or fleshy fungus consists of long filaments of cells joined together called hyphae.
• Hyphae can grow to immense proportions, such as a single fungus in Oregon extending across 3.5 miles.
• Septate hyphae contain cross-walls (septa) that divide them into distinct, uninucleate (one-nucleus) cell-like units.
• Coenocytic hyphae lack septa and appear as long, continuous cells with many nuclei.
• Hyphae grow by elongating at the tips and can form new hyphae from fragments.
• Vegetative hyphae obtain nutrients.
• Reproductive (aerial) hyphae are concerned with reproduction and project above the surface, often bearing reproductive spores.
• A mycelium is a filamentous mass formed by hyphae under suitable environmental conditions, visible to the unaided eye.

Yeast

• Yeasts are non-filamentous, unicellular fungi that are typically spherical or oval.
• They are widely distributed in nature, often found as a white powdery coating on fruits and leaves.
• Budding yeasts, like Saccharomyces, divide unevenly, forming a bud on the outer surface that elongates and eventually breaks away.
• One yeast cell can produce up to 24 daughter cells by budding.
• Pseudohyphae are short chains of cells formed by buds that fail to detach themselves.
• Candida albicans uses pseudohyphae to invade deeper tissues.
• Fission yeasts, like Schizosaccharomyces, divide evenly to produce two new cells through elongation and nuclear division.
• Yeasts are capable of facultative anaerobic growth, allowing them to survive in various environments.
• With oxygen, yeasts perform aerobic respiration, metabolizing carbohydrates to carbon dioxide and water.
• Without oxygen, yeasts ferment carbohydrates, producing ethanol and carbon dioxide, used in brewing, wine-making, and baking industries.
• Dimorphic fungi exhibit two forms of growth: mold-like (vegetative and aerial hyphae at 25°C) and yeast-like (budding at 37°C).

Fungal Life Cycle

• Both sexual and asexual reproduction in fungi occurs by spore formation.
• Fungi are identified by their spore type.
• After a mold forms a spore, the spore detaches and germinates into a new mold.
• Fungal spores can survive for extended periods in dry or hot environments, but most do not exhibit extreme tolerance.

Spores: Asexual & Sexual

• Asexual spores result from fragmentation of hyphae in filamentous fungi.
• Sexual spores result from the fusion of nuclei from two opposite mating strains of the same species of fungus, occurring less frequently than asexual spores.
• Asexual spores are produced by an individual fungus through mitosis and subsequent cell division.

Types of Asexual Spores

• Conidiospores (conidia) are unicellular or multicellular spores not enclosed in a sac, produced from a conidiophore.
• Arthroconidia are formed by the fragmentation of a septate hypha into single, slightly thickened cells, like Coccidioides immitis.
• Blastoconidia consist of buds coming off the parent cell, like Candida albicans and Cryptococcus.
• A chlamydoconidium is a thick-walled spore formed by rounding and enlargement within a hyphal segment, like C. albicans.
• Sporangiospores are formed within a sporangium (sac) at the end of an aerial hypha called a sporangiophore and can contain hundreds of sporangiospores, like Rhizopus.

Sexual Spores

• Sexual reproduction in fungi 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.

Nutritional Adaptations for Fungi

• Fungi are generally adapted to environments hostile to bacteria and absorb nutrients rather than ingesting them.
• Fungi grow better in an environment with a pH of about 5, which is too acidic for most common bacteria.
• Almost all molds are aerobic, while most yeasts are facultative anaerobes.
• Most fungi are more resistant to osmotic pressure than bacteria and can grow in relatively high sugar or salt concentrations.
• Fungi can grow on substances with very low moisture content, generally too low to support bacterial growth.
• Fungi require somewhat less nitrogen than bacteria for an equivalent amount of growth.
• They can metabolize complex carbohydrates, such as lignin, that most bacteria cannot use for nutrients.

Medically Important Fungi

• Zygomycota (conjugation fungi or saprophytic molds) have coenocytic hyphae.
• Microsporidia are unusual eukaryotes with no mitochondria or microtubules and are obligate intracellular parasites.
• Ascomycota (sac fungi) are molds with septate hyphae.
• Basidiomycota (club fungi).

Fungal Diseases

• Mycoses refers to any fungal infection and are generally chronic (long-lasting) because fungi grow slowly.
• Mycoses are classified into five groups:
  • Systemic: Infection in any part of the body, usually caused by fungi that live in the soil, via inhalation and noncontagious.
  • Subcutaneous: Fungal infection beneath the skin, caused by saprophytic fungi.
  • Cutaneous: Dermatomycoses/cutaneous mycosis caused by dermatophytes, contagious.
  • Superficial: Localized along hair shafts and in superficial (surface) epidermal cells.
  • Opportunistic: Generally harmless in its normal habitat but can become pathogenic in a host who is seriously debilitated, under treatment with broad-spectrum antibiotics, immunosuppressed, or has a lung disease.

Economic Effects of Fungi

• In biotechnology, Aspergillus niger is used to produce citric acid for foods and beverages since 1914.
• Saccharomyces cerevisiae is used to make bread and wine, and is genetically modified to produce proteins like hepatitis B vaccine.
• Trichoderma is used commercially to produce the enzyme cellulase to produce a clear fruit juice.

Biological Control of Pests

• In 1990, Entomophaga unexpectedly proliferated and killed gypsy moths.
• Coniothyrium minitans feeds on fungi that destroy soybeans and other bean crops.
• Paecilomyces fumosoroseus is used as a biological alternative to chemicals to kill termites.

Undesirable Effects of Fungi (Agriculture)

• Mold spoilage of fruits, grains, and vegetables is common.
• Cryphonectria parasitica (fungal blight) kills chestnut tree shoots.
• Dutch elm disease, caused by Ceratocystis ulmi, blocks the afflicted tree’s circulation.

Short Quiz

• Discuss the Kingdom Fungi in detail, highlighting its basic cellular characteristics, structural organization, modes of reproduction, and methods of nutrient acquisition.
• Identify the fungal phylum to which a typical mushroom belongs.

Lichens Functional Anatomy & Reproduction

• Lichens are a combination of a green alga (or a cyanobacterium) and a fungus in a mutualistic relationship.
• The lichen is very different from either the alga or fungus growing alone, and if the partners are separated, the lichen no longer exists.
• With ~13,500 species of lichens occupy quite diverse habitats, are often the first life forms to colonize newly exposed soil or rocks, trees, concrete structures, rooftops, basically almost everywhere.
• Lichens are some of the slowest-growing organisms on Earth.
• Parts include: thallus, medulla, rhizines or holdfast & cortex
• After incorporation into a lichen thallus, the alga continues to grow, and the growing hyphae can incorporate new algal cells.

Lichens Morphologic Categories

• Crustose lichens grow flush or encrusted onto the substrate.
• Foliose lichens are more leaflike.
• Fructicose lichens have fingerlike projections.
• When the alga is associated with a fungus, the algal plasma membrane is more permeable, and up to 60% of the products of photosynthesis are released to the fungus.
• The alga receives attachment (rhizines) and protection from desiccation (cortex) from the fungus.

Importance of Lichens

• Lichens are used as dyes for clothing in ancient Greece and other parts of Europe.
• Usnic acid from Usnea is used as an antimicrobial agent in China.
• Erythrolitmin, the dye used in litmus paper, is extracted from a variety of lichens.
• Some lichens or their acids can cause allergic contact dermatitis in humans.
• Lichens are used for biomonitoring, attracting cations (+ ions) and thus, air quality can be ascertained.
• Lichens are the major food for tundra herbivores such as caribou and reindeer.
• After the 1986 Chernobyl nuclear disaster, 70,000 reindeer had to be destroyed because of high levels of radiation absorbed by lichens.

Algae Characteristics

• “Algae” is a way to describe photoautotrophs that lack the roots and stems of plants.
• Some algae are unicellular, others are filamentous, and a few have thalli.
• Algae are mostly aquatic in cool temperate waters, although some are found in soil or on trees when sufficient moisture is available.
• Relatively simple eukaryotic photoautotrophs that lack the tissues (roots, stem, and leaves) of plants but can be unicellular or multicellular.
• Algae mostly inhabit the ocean, in the areas with available appropriate nutrients (photic zone)
• Vegetative structures include thallus (body) that is covered with cells that carry out photosynthesis.
• Multicellular algae have holdfasts (anchor), stipes (stem-like), blades (leaf-like), and pneumatocysts (gas-filled bladders).

Algal Life Cycle

• Algae can reproduce sexually and asexually.
• Reproduction may change from asexual to sexual depending on the conditions.
• Some species alternate generations so that the offspring resulting from sexual reproduction reproduce asexually.
• Unicellular alga divides via mitosis and cytokinesis
• Multicellular algae with thalli and filamentous forms can fragment

Algal Nutrition & Classification

• Most algae are autotrophs (photosynthetic), oomycotes, or fungal-like algae are chemoheterotrophs.
• Chlorophyll a (a light-trapping pigment) and accessory pigments are responsible for the distinctive colors of many algae.
• Algae are classified according to their rRNA sequences, structures, pigments, and other qualities

Kingdom Stramenophila

• Macroalgae, Diatoms, Dinoflagellates, and Water molds

Macroalgae

• Brown Algae (Kelp) are macroscopic algae, reaching up to 50m in length found mostly in coastal waters
• They have phenomenal growth rate, exceeding 20cm per day.
• Algin, a thickener used in many foods and non-food products, is extracted from their cell walls
• Laminaria japonica, a brown algae, is used to induce vaginal dilation.

Red Algae

• Red algae have delicately branched thalli and can live at greater ocean depths than other algae.
• The red pigments enable red algae to absorb the blue light that penetrates deepest into the ocean.
• Carrageenan, a gelatinous material, comes from species of red algae and is used as agar and a thickening ingredient.
• Green algae have cellulose cell walls, contain chlorophyll a and b, and store starch.
• They are believed to have given rise to terrestrial plants and form grass-green scum in ponds.

Microalgae

• Diatoms and Dinoflagellates
• Diatoms are phytoplankton with complex cell walls of pectin and silica forming symmetrical bodies and store energy as oil.
• The first reported cases of diatom toxicity was domoic acid toxicosis
• Dinoflagellates are unicellular algae called plankton and have cellulose embedded in the plasma membrane.
• Some produce neurotoxins killing fishes, mammals even humans
• Examples: Karenia brevis release neurotoxin, and Genus Alexandrium produce saxitoxins which causes paralytic shellfish poisoning (PSP); causes red tide

Water Molds

• Oomycota
• Decomposers that form the cottony masses on dead algae and animals, usually in fresh water
• Asexually, the oomycotes resemble the zygomycete fungi.
• However, oomycote spores, called zoospores have two flagella; fungi do not have flagella
• DNA analyses showed close relatedness to Stramenophiles

Roles of Algae in Nature

• Algae are an important part of any aquatic food chain.
• Algae fix carbon dioxide into organic molecules that can be consumed by chemoheterotrophs
• Estimated that 80% of the Earth’s O2 is produced by planktonic algae.
• Periodic increases in numbers of planktonic algae are called algal blooms, which are caused by pollution.
• Much of the world’s petroleum was formed from diatoms and other planktonic organisms.
• Many unicellular algae are symbionts in animals, such as dinoflagellates in the giant clam Tridacna.

Protozoa Functional Anatomy & Reproduction

• Protozoa means “first animals,” referring to its animal-like nutrition and are unicellular, eukaryotic organisms with diverse cellular structures.
• They inhabit water and soil.
• The vegetative state is called a trophozoite and feeds upon bacteria and small particulate nutrients
• Relatively few of the nearly 20,000 species of protozoa cause human disease.
• Some are photosynthetic, and many have complex life cycles that enable them to get from one host to the next.

Protozoan Life Cycle

• Protozoa reproduce asexually by fission, budding, or schizogony, in which the nucleus undergoes multiple divisions before the cell divides.
• Sexual reproduction is observed in some, particularly on the ciliates like Paramecium via conjugation
• Some protozoa produce gametes (gametocytes), which are haploid sex cells that fuse to form a diploid zygote during reproduction.

Encystment

• Under certain adverse conditions, some protozoa produce a protective capsule called a cyst.
• allows for survival when food, moisture, or oxygen are lacking or when temperatures are not suitable
• The cyst formed by members of the phylum Apicomplexa is called an oocyst.

Protozoan Nutrition

• Protozoa are mostly aerobic heterotrophs, although many intestinal protozoa are capable of anaerobic growth.
• They live in areas with a large supply of water.
• Some transport food across the plasma membrane, while others have a protective covering, or pellicle, and require specialized structures to take in food.
• Ciliates take in food by waving their cilia toward a mouthlike opening called a cytostome.
• Amebae engulf food by surrounding it with pseudopods
• Digestion takes place in membrane-enclosed vacuoles, and waste is eliminated through the plasma membrane

Supergroup (Superkingdom) Excavata

• Single-celled eukaryotes with a feeding groove in the cytoskeleton
• Most are spindle-shaped and possess flagella
• Includes 2 Phyla that lacks mitochondrion (Diplomonads & Parabasalids) and the phylum Euglenozoa
• Diplomonads - mitochondrial remnant organelles, called mitosomes; anaerobic; has 2 similar haploid nuclei; have four pairs of locomotor flagella
• Parabasalids - named for the parabasal apparatus, which consists of a Golgi complex associated with cytoskeletal fibers; have hydrogenosomes
• Some have undulating membrane & axostyle, a membrane bordered by a flagellum
• Euglenozoa include Euglenoids & Hemoflagellates
• Euglenoids are photoautotrophs; some are facultative chemoheterotrophs with pellicle; moves by means of flagella; have a red eyespot
• Hemoflagellates are transmitted by the bites of blood-feeding insects; with slender bodies and undulating membrane
• Examples: Trypanosoma brucei (African sleeping sickness) via tsetse fly; Trypanosoma cruzi (Chagas disease) via kissing bug

Amebae

• Amebae move by extending blunt, lobe-like projections of the cytoplasm called pseudopods
• Entamoeba histolytica is the only pathogenic ameba found in the human intestine. E. dispar & E. histolytica (amoebic dysentery)
• E. histolytica have galactose-binding lectins that causes cell lysis
• Acanthamoeba (could cause blindness) & Balamuthia (granulomatous amebic encephalitis) are water free-living amoeba

Apicomplexa

• Non-motile protozoans (mature forms) are obligate intracellular parasites
• They are characterized by the presence of a complex of special organelles at the apexes (tips) of their cells
• These organelles in these apical complexes contain enzymes that penetrate the host’s tissues.
• They have a complex life cycle that involves transmission between several hosts

Apicomplexa Examples

• Plasmodium, the causative agent for malaria, grows by sexual reproduction in the Anopheles mosquito
• An Anopheles carrying the infective stage of Plasmodium, called a sporozoite, bites a human
• Sporozoites undergo schizogony in liver cells and produce thousands of progeny called merozoites, which infect red blood cells
• The young trophozoite looks like a ring, called a ring stage
• Definitive Host – primary host; organism in which a parasite sexually reproduces
• Intermediate Host forms of a parasite – an organism that supports the immature or nonreproductive
• Babesia microti causes Babesiosis characterized by fever and anemia in immunosuppressed individuals transmitted by the tick Ixodes scapularis
• Toxoplasma gondii causes toxoplasmosis.
• Cryptosporidium, the causative agent for cryptosporidiosis, lives inside the cells lining the small intestine

Ciliates

• Ciliates have cilia that are similar to but shorter than flagella, arranged in precise rows on the cell
• Balantidium coli (balantidiasis) the only ciliate that is a human parasite; the causative agent of a severe dysentery
• Cysts enter the large intestine, into which the trophozoites are released, producing proteases that destroy host cells.

Slime Mold

• Slime molds are closely related to amebae and are placed in the phylum Amoebozoa

Types of Slime Molds

• Cellular slime molds are typical eukaryotic cells that resemble amebae, ingesting fungi and bacteria by phagocytosis
• Cellular slime molds are a focus of study on cellular migration and aggregation
• Unfavorable condition causes the amoeboid cells to aggregate via chemical cyclic AMP forming a stalk and spore cap
• Plasmodial slime molds exist as a mass of protoplasm with many nuclei (multinucleated), called a plasmodium
• The plasmodium moves as a giant amoeba, engulfing organic debris & bacteria through muscle-like protein microfilaments.
• Cytoplasmic streaming is observed allowing changes in speed & direction so that the oxygen and nutrients are evenly distributed
• Separation into groups of protoplasm each forms a stalked sporangium, in growth is dependent on food supply & moisture