CHAPTER 12 FUNGI, ALGAE, PROTOZOA, AND MULTICELLULAR PARASITES

	FUNGI	ALGAE	PROTOZOA	HELMINTHS
KINGDOM	FUNGI	PROTISTA	PROTISTA	ANIMALIA
NUTRITIONAL TYPE	CHEMOHETERO-TROPH	PHOTOAUTO-TROPH	CHEMOHETERO-TROPH	CHEMOHETERO-TROPH
MULTICELLULARITY	ALL, EXCEPT YEASTS	SOME	NONE	ALL
CELLULAR ARRANGEMENT	UNICELLULAR, FILAMENTOUS, FLESHY	UNICELLULAR, COLONIAL FILAMENTOUS, TISSUES	UNICELLULAR	TISSUES AND ORGANS
FOOD ACQUISITION METHOD	ABSORPTIVE	ABSORPTIVE	ABSORPTIVE, INGESTIVE	INGESTIVE, ABSORPTIVE
CHARACTERISTIC FEATURES	SEXUAL AND ASEXUAL SPORES	PIGMENTS	MOTILITY; SOME FORM CYSTS	MANY HAVE ELABORATE LIFE CYCLES
EMBRYO FORMATION	NONE	NONE	NONE	ALL

FUNGI

The study of fungi is called mycology. Like all microbes, fungi are both beneficial and harmful to humans. Of about 100,000 species only about 200 are pathogenic to humans and animals. Harmful effects include damage to crops and diseases of humans and domestic animals. Beneficial effects for humans include foods and production of alcohol and drugs. Fungi produce enzymes that allow them to decompose dead plant matter. Many plants have associated symbiotic fungi called mycorrhizae, which help their roots absorb nutrients.

All fungi are chemoheterotrophs, obtaining energy and carbon from organic compounds. With the exception of a very few anaerobic fungi, most are aerobic or facultatively anaerobic. Among the microscopic fungi, yeasts are unicellular and molds are multicellular.

CHARACTERISTICS OF FUNGI

Specific yeasts are identified mainly by biochemical tests. Multicellular fungi are identified on the basis of physical appearance, colony characteristics, and reproductive spores.

1. Vegetative structures—these are fungal colonies composed of the cells involved in catabolism and growth.

a. Molds and Fleshy Fungi---the thallus (body) of a mold or fleshy fungus consists of long filaments of cells joined together. The filaments are called hyphae. Individual hyphae can range from microscopic to enormous. One fungus growing in Oregon is estimated to have hyphae extending across 3.5 miles.

In most molds the hyphae are divided into uninucleate cell-like units by cross-walls called septae—these hyphae are called septate hyphae and usually have small openings in the septae that make the “cells” continuous. In a few classes of fungi, the hyphae do not contain septae and are called coenocytic hyphae.

Hyphae grow by elongating at the tips. When a piece breaks off, it can grow to form a new hypha. The portion of a hypha that obtains nutrients is called the vegetative hypha; the portion concerned with reproduction projects above the surface of the medium and is called the reproductive or aerial hypha. Aerial hyphae often bear reproductive spores. When conditions are suitable, the hyphae grow to form a visible mass called a mycelium, which is visible without magnification.

b. Yeasts—nonfilamentous, unicellular fungi that are spherical or oval in shape. They are widely distributed in nature and may make a white powdery coating on fruits and leaves. Some yeasts undergo binary fission to produce two cells of equal size and are called fission yeasts. Others, such as Saccharomyces reproduce by budding. The parent cell forms a bulge on the surface. The nucleus divides and one nucleus migrates into the bud. The cell wall divides the bud from the parent, and the bud eventually breaks away.

One yeast cell can produce as many as 24 daughter cells by budding. Some yeasts produce buds that do not break away, and form a short chain of cells called a pseudohypha. Candida albicans, which causes thrush and vaginitis in humans, uses pseudohyphae to invade deeper into tissues. Growing on lab media, yeasts produce colonies similar in appearance to bacterial colonies.

Yeasts can grow aerobically or as facultative anaerobes, so they are able to survive in various environments. Species of Saccharomyces are growing aerobically in bread dough to make it rise and anaerobically to produce ethanol in the brewing industry.

c. Dimorphic fungi---this means “two forms.” Some fungi, including most of the pathogenic species, can grow either as a mold or as a yeast. In the mold form, they grow vegetative and aerial hyphae; in the yeast form they reproduce by budding. In pathogenic fungi this depends on temperature—at 37⁰ C the fungus is yeastlike and at 25⁰ C it is moldlike. Other fungi may change type due to CO₂ concentration.

2. Life Cycle—filamentous fungi can reproduce asexually by fragmentation of their hyphae. In addition, fungi reproduce by forming both sexual and asexual spores. The characteristics of these spores are an important means of identifying fungi. Unlike bacterial endospores, fungal spores are intended as a means of reproduction. Thousands of spores can be produced and each spore can grow into a new organism. Fungal spores are somewhat resistant to heat and drying, but not nearly to the same extent as bacterial endospores.

Spores are formed from aerial hyphae in various ways, and can be sexual or asexual.

a. Asexual spores—formed by the hyphae of one organism. When these germinate, the organism they produce is genetically identical to the original. They are produced by mitosis and cell division. Types:

1) Conidiospores—unicellular or multicellular spores not enclosed in a sac. They are produced in a chain at the end of a stalk-like conidiophore. Aspergillus is an example. Two special types of conidiospores:

a) Arthrospores—fragmentation of a septate hypha into single cells. Coccidiodes immitis is an example.

b) Blastoconidia—special type of conidiospore that consist of buds coming off the parent cell. Candida albicans and Cryptococcus are examples.

2) Chlamydospores—thick-walled spore formed by rounding and enlargement within a hyphal segment. Candida albicans may also produce these spores.

3) Sporangiospores—formed within a sac called a sporangium at the end of an aerial hypha called a sporangiophore. Rhizopus is an example.

b. Sexual spores---these are produced much less frequently than asexual spores. Organisms growing from sexual spores will combine the genetic characteristics of both parents. They are produced by sexual reproduction involving fusion of nuclei from opposite mating strains of the same species.

For classification, fungi are placed into divisions according to the type of sexual spores they produce. In laboratory conditions, most fungi produce only asexual spores, so these are the basis for clinical identification.

NUTRITIONAL ADAPTATIONS

Fungi may adapt well to environments that do not support growth of bacteria. To compare the two groups:

1. Fungi usually prefer a pH of about 5, which is too acid for most bacteria

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

3. Most fungi are more resistant to high osmotic pressure than bacteria, so they are able to grow in jellies, fruit juice, salted meats, etc.

4. Fungi can grow on substances with a very low moisture content, much lower than that required by bacteria (baked goods, for example)

5. Fungi require somewhat less nitrogen than bacteria

6. Fungi can break down complex carbohydrates, such as wood, that most bacteria cannot.

MEDICALLY IMPORTANT DIVISIONS OF FUNGI

Only the divisions of fungi containing pathogens are included here, but not all members of these divisions listed are pathogenic. Like bacteria, the great majority of fungi are harmless or beneficial.

1. Zygomycota---saprophytic molds that have coenocytic hyphae. Sexual spores are zygospores, large spores enclosed in a thick wall. Asexual spores are sporangiospores.

2. Ascomycota (sac fungi)—includes molds with septate hyphae and some yeasts. Their asexual spores are usually conidiospores produced in long chains. These spores freely detach and float in the air like dust. Sexual ascospores are produced in a saclike structure called an ascus.

3. Basidiomycota (club fungi)—have septate hyphae and include the fungi that produce mushrooms. Basidiospores are formed on a base pedestal called a basidium, usually 4 basidiospores per basidium. Some also produce asexual conidiospores.

These first 3 groups are call telomorphs, which means they produce both sexual and asexual spores.

4. Anamorphs—a few fungi have not yet been found to produce sexual spores. All have septate hyphae and produce asexual chlamydospores, arthrospores, and conidiospores, and well as reproduction by budding. Some of these will be removed to another category as sexual spores are identified. (Remember, mostly asexual spores are produced in lab conditions, so finding the sexual spores can be difficult.) A number of pathogens were once placed in this group and then later moved as sexual spores were identified. This group was previously named Deuteromycota. rRNA studies have shown that most of these are related to Ascomycota.

DIVISION	GROWTH CHARACTERISTICS	ASEXUAL SPORES	HUMAN PATHOGENS
ZYGOMYCOTA	NONSEPTATE HYPHAE	SPORANGIOSPORES	Rhizopus Mucor
ASCOMYCOTA	DIMORPHIC ------------------------------ SEPTATE HYPHAE, STRONG AFFINITY FOR KERATIN	CONIDIOSPORES ------------------------------ CONIDIOSPORES ------------------------------ ARTHROSPORES	Aspergillus Blastomyces dermatidis Histoplasma capsulatum ------------------------------ Microsporum Trichophyton
BASIDIOMYCOTA	SEPTATE HYPHAE, INCLUDES RUSTS, SMUTS, AND OTHER PLANT PATHOGENS; YEASTLIKE ENCAPSULATED CELLS	CONIDIOSPORES	Cryptococcus neoformans
ANAMORPHS	SEPTATE HYPHAE ------------------------------ DIMORPHIC ------------------------------ YEASTLIKE, PSEUDOHYPHAE ------------------------------ UNKNOWN	CONIDIOSPORES ------------------------------ CONIDIOSPORES ARTHROSPORES ------------------------------ CHLAMYDOSPORES ------------------------------ UNKNOWN	Epidermophyton Sporothrix schenckii Coccidiodes immitis ----------------------------- Candida albicans ------------------------------ Pneumocystis

FUNGAL DISEASES

Any fungal infection is called a mycosis. Mycoses are generally long-lasting, chronic infections.

1. Systemic mycoses—fungal infections deep within the body. They are usually caused by fungi that live in the soil and inhalation of spores is the common route of infection. These infections therefore usually begin in the lungs and may spread to other tissues. They are not transmitted from person to person. Histoplasmosis and coccidioidomycosis are two examples.

2. Subcutaneous mycoses—fungal infections beneath the skin, usually caused by spores or mycelial fragments of soil organisms that enter through a puncture wound. Sporotrichosis is an example.

3. Dermatomycoses or cutaneous mycoses—these infect only the epidermis, hair, and nails. The fungus organisms can be called dermatophytes. All secrete an enzyme called keratinase that breaks down keratin in the hair, skin, and nails. These can be spread from person to person by direct contact or by contact with objects carrying the fungus---manicure tools, tanning beds, barber’s scissors or clippers, etc.

4. Superficial mycoses---affect only hair shafts and surface epidermal cells.

5. Opportunistic pathogens---these are organisms that are generally harmless, but can become pathogenic when the host is debilitated or traumatized, when antibiotics have changed the normal balance between fungi and bacteria, or when the immune system is suppressed by drugs or AIDS.

a. Stachybotrys---this organism has been found growing in houses on walls that have been damaged by water. Its toxin has caused pulmonary hemorrhage and death in infants.

b. Mucormycosis---Rhizopus or Mucor—occurs mostly in patients with diabetes mellitus, leukemia, or suppressed immune systems.

b. Aspergillosis---Aspergillus--affects mostly people with chronic lung disease or cancer.

c. Yeast infection (candidiasis)—Candida albicans—thrush is an infection in the mouth, vaginal candidiasis is also common.

ECONOMIC EFFECTS OF FUNGI

Beneficial effects:

1. Saccharomyces cerevisiae (a yeast) is used to make bread and wine. It has also been genetically engineered to make proteins, including Hepatitis B vaccine.

2. Saccharomyces and another yeast, Torulopsis, are used as protein supplements for humans and cattle.

3. Trichoderma is used to produce the enzyme cellulase, which removes plant cell walls to produce a clear fruit juice.

4. Taxomyces produces taxol, an anticancer drug.

5. Biological control of pests

a. Entomorphaga can kill gypsy moths

b. One fungus, Candida oleophila, can help control other more harmful fungi on fruits

6. Aspergillus niger is used to produce citric acid.

Undesirable effects:

1. Spoilage of fruits, grains, and vegetables.

2. Cryphonectria parasitica killed almost all of the chestnut trees in this country

3. Dutch elm disease, Ceratocystis ulmi has killed most of the elm trees

LICHENS

These are combinations of a green alga and a fungus. They are placed in the kingdom Fungi and classified by the fungus part. The relationship between the two is mutualism--both benefit. Lichens can live in areas where neither alga nor fungus alone could survive. Examples are newly exposed soil, rocks, trees, concrete, etc. Their main importance in nature is serving as food for arctic tundra caribou and reindeer.

ALGAE

Algae are mostly aquatic, although some are found in soil or on trees occasionally. Most algae are found in cool temperate waters, although some are found in Antarctic waters and some in tropical zones.

CHARACTERISTICS OF ALGAE

Algae are simple eukaryotic photoautotrophs. Most are found in the ocean. Algae can be unicellular or multicellular.

1. Vegetative structures—the body of a multicellular alga is called a thallus. This would include such algae as seaweed. The thalli consist of branched holdfasts to anchor the algae in place, stemlike stipes and leaflike blades. The cells covering the thallus carry out photosynthesis, and algae also can absorb nutrients from the water. Some algae are buoyed by a floating, gas-filled bladder called a pneumatocyst.

2. Life Cycle—all algae can reproduce asexually. Multicellular algae can fragment. Unicellular algae divide by mitosis and cytokinesis. Some algae also reproduce sexually. In some of these asexual reproduction is most common and sexual reproduction only occurs under special conditions. Other species alternate, reproducing asexually and then sexually in alternating generations.

3. Nutrition—almost all algae are photoautotrophs and are found in the photic (light) zone in bodies of water. Chlorophyll and sometimes other pigments are responsible for the colors of algae and their ability to carry out photosynthesis.

SELECTED PHYLA OF ALGAE

Algae are classified according to their rRNA, structures, pigments, and other qualities.

1. Brown algae (kelp) are macroscopic and may reach lengths of 50 meters. Most are found in coastal waters and grow very rapidly. Algin, a thickener used in foods such as ice cream, is extracted from the cell walls. This product is also used in hand lotions.

2. Red algae—these live deeper in the ocean than other algae. Agar is extracted from them. Another product, carageenan, comes from a species of red algae known as Irish moss and is used as a thickening agent in evaporated milk, ice cream and drugs. Some of these produce a lethal toxin.

3. Green algae—these have cellulose walls and store starch. Green algae may have given rise to terrestrial plants. Most green algae are microscopic, and may be either unicellular or multicellular. Some form grass-green scum in ponds.

4. Diatoms—unicellular or filamentous algae with complex cell walls that consist of pectin and silica. Some produce a toxin called domoic acid, which can affect people, marine mammals, and birds that eat mussels that have fed on diatoms.

5. Dinoflagellates—unicellular algae called plankton. They have cellulose embedded in the plasma membrane. Some produce neurotoxins which may affect fish, marine mammals, and humans who eat mollusks such as mussels and clams. Large concentrations of one toxic genus, Alexandrium, give the ocean a red color and are called red tides. The neurotoxin involved causes paralytic shellfish poisoning. A disease called ciguatera occurs when the toxin of the dinoflagellate Gambierdiscus toxicus is concentrated in fish.

6. Oomycota (water molds)—once classified as fungi, they are now grouped with the algae. They are different because they do ot carry on photosynthesis and are plant parasites. In Ireland in the mid-1800'2, about 1 million people died as a result of a famine caused by Phytophora (potato blight). Other species of this genus affect trees.

ROLES OF ALGAE IN NATURE

1. Algae are important in the food chain.

2. In carrying out oxygenic photosynthesis, it is estimated that algae produce up to 80%

of earth’s oxygen.

3. Much of the world’s petroleum was formed from diatoms and other plankton.

4. Many unicellular algae live in symbiosis with animals.

5. Algal blooms occur and are responsible for red tides and the associated toxins. When the large amounts of algae die, their decomposition depletes the water of oxygen.

PROTOZOA

This group consists of unicellular, eukaryotic organisms belonging to the kingdom Protista. They live in water and soil, and all are chemoheterotrophs. The vegetative stage is known as a trophozoite. Only a few of the 20,000 known species cause disease, and some are considered part of the normal inhabitants of other animals.

CHARACTERISTICS

1. Life cycle—protozoa reproduce asexually by fission, budding, or schizogony (multiple fission). In this process the nucleus undergoes multiple divisions before the cell divides into numerous daughter cells, including a little of the cytoplasm in each.

Some protozoa also reproduce sexually. The ciliates such as Paramecium undergo a process called conjugation. Two cells temporarily join, and a haploid nucleus from each cell migrates to the other cell, thus exchanging genetic material. Other protozoa produce gametes (haploid sex cells) which fuse to form a diploid zygote.

2. Encystment—under adverse conditions, some protozoa produce a protective capsule called a cyst, which permits the organism to survive under harmful conditions such as lack of food, moisture, or oxygen, temperature extremes, or the presence of toxic chemicals. In some parasitic species, this is the only form that can survive outside a host. Cysts formed by the phylum Apicomplexa are called oocysts.

3. Nutrition—most are aerobic heterotrophs, although some protozoa living in the intestines can grow anaerobically. Euglena is sometimes classified as a protozoan and sometimes as flagellated algae, since it can grow as a heterotroph in the dark and switch to photosynthesis in light.

All protozoa require surroundings with plenty of water. Some transport their food across the plasma membrane. Others have a stiff outer covering called a pellicle, and require specialized structures to allow the intake of food. Ciliates use their cilia to wave food toward a special mouthlike area called the cytostome. Amoebas surround food with pseudopods and take it in by phagocytosis. Inside all protozoa, food is digested in membrane-enclosed vacuoles, and waste may either be eliminated through the plasma membrane or through a specialized anal pore.

MEDICALLY IMPORTANT PHYLA OF PROTOZOA

We will study only those groups that contain pathogens.

1. Archaezoa--eukaryocytes that lack mitochondria. Many of these live in symbiosis in the digestive tracts of animals. Most have two or more flagella for movement. Some have a membrane attached to the flagella, called an undulating membrane.

a. Trichomonas vaginalis--lives in the vagina or the male urinary tract. Trichomoniasis is a sexually transmitted disease, although it can also sometimes spread other ways. This organism does not form cysts.

b. Giardia lamblia--lives in the small intestine of humans and other mammals. Cysts can survive in the environment.

2. Microspora--obligate intracellular parasites that lack mitochondria and microtubules. Cause chronic diarrhea and keratoconjunctivitis, often in AIDS patients.

3. Amoebozoa--the amoebas. These move by pseudopods--they extend bits of their cytoplasm in the direction they want to go and then the rest of the cell sort of flows into the pseudopod.

a. Entamoeba histolytica---this pathogenic amoeba is found in the human intestine and causes a disease known as amoebic dysentery. It is transmitted from person to person by ingestion of cysts that are excreted in the feces of infected persons. It burrows into the intestinal wall and feeds mainly on red blood cells.

b. Acanthamoeba species grow in water and can infect the cornea.

c. Balamuthia—grow in water and can cause brain abscesses, mostly in persons with compromised immune systems.

4. Apicomplexa—these are nonmotile in their mature forms. All members of this group are obligate intracellular parasites (some groups contain hundreds or thousands of non-parasitic species and only a few parasites). They all produce enzymes that penetrate hosts' tissues. All have complex life cycles, involving more than one type of host.

a. Plasmodium species (4 different species) are the causative agents of malaria. Although rare in the United States, worldwide this is the number one infectious disease, causing large numbers of deaths each year. This parasite is spread to humans by the bite of the Anopheles mosquito.

The life cycle is:

1) A mosquito carrying the infective state of Plasmodium (called a sporozoite) bites a human and injects sporozoites into the bloodstream. They are carried to the liver.

2) In the liver they undergo schizogony and produce thousands of a form known as a merozoite. This is asexual reproduction.

3) Merozoites enter the bloodstream and each infects a red blood cell.

4) Merozoites can be seen inside the red blood cell as a clear ring inside which the nucleus and

cytoplasm are visible. This is called the ring stage.

5) The ring stage enlarges and divides repeatedly. (More asexual reproduction.)

6) Eventually the red blood cell ruptures and releases the merozoites into the blood. As the blood cell ruptures, the waste products of the merozoites also enter the blood, and cause chills and fever. Most of the merozoites invade new red blood cells and repeat the cycle. A few of the merozoites change and develop into male and female sexual forms (gametocytes). The gametocytes circulate in the blood and cause no further damage.

7) However, if gametocytes are picked up by an Anopheles mosquito feeding on the blood, they enter the intestine of the mosquito and begin the cycle of sexual reproduction.

8) Male and female gametocyte unite to form a zygote. The zygote forms an oocyst, in which cell division occurs and numbers of sporozoites are formed.

9) The oocyst ruptures and the sporozoites migrate to the salivary glands of the mosquito, where they are ready to infect a new host bitten by the mosquito.

In this cycle the mosquito is called the definitive host because it harbors the stage undergoing sexual reproduction. The human is the intermediate host, because reproduction inside it is asexual.

Malaria is diagnosed by observing blood smears for the presence of Plasmodium. The patient undergoes periodic episodes of chills and fever, occurring as the merozoites are released from red blood cells. The time period between can vary according to the species of Plasmodium, but it is always some multiple of 24 hours. This is timed according to fluctuations in body temperature of the host so that the gametocytes are mature at night when mosquitoes are most likely to be feeding.

b. Babesia microti—transmitted by a tick, this organism causes fever and anemia in immunosuppressed individuals. It is also a parasite of red blood cells.

c. Toxoplasma gondii---life cycle involves cats (this is why pregnant ladies are not supposed to handle kitty litter). The trophozoites are called tachyzoites and reproduce by both sexual and asexual reproduction in infected cats (which usually show no symptoms). Oocysts containing sporozoites are excreted in the feces. If ingested by humans or other animals, the sporozoites emerge as tachyzoites, which can reproduce in the tissues of the new host. This is usually not serious for the host, except for people with poorly functioning immune systems and pregnant women. Great damage can be done to a developing fetus.

d. Cryptosporidium---this is a newly recognized parasite of humans. It usually causes vomiting and diarrhea which lasts for weeks, but is normally fatal only in people lacking normal immune function, including the elderly. There it can also cause respiratory complications and infections of the gallbladder, and can be the major cause of death. It can be transmitted to humans through the feces of cows, rodents, dogs, and cats. Oocysts are ingested, and release sporozoites, which can infect cells in the host or be released with feces. It has caused epidemics through contaminated water supplies.

e. Cyclospora cayetanensis---even more recently discovered, it has caused diarrhea associated with fruit & raw veggies

5. Ciliophora