There Are Astonishing Numbers of Organisms in a Single Drop of Pond Water. Some of These

PROTISTS

There are astonishing numbers of organisms in a single drop of pond water. Some of these tiny organisms propel themselves with whipping flagella, while others creep along by means of blob-like appendages. Some resemble miniature jewelry; others look like tumbling green globes. These beautiful creatures belong to a group of unicellular eukaryotes known as protists.

Protists are an extremely diverse assortment of organisms. Some protists are autotrophic (make their own food with chlorophyll and sunlight) like plants; others are heterotrophic (ingest their food) like animals. Most protists are aquatic and are found almost anywhere there is water. The two types of protists we will cover are algae, which are not pathogenic but cause problems in aquariums and swimming pools, and protozoa, which are single-celled animals (we will only discuss the protozoas that cause disease).

ALGAE

These are the producers of the ecosystem because they have chloroplasts which contain chlorophyll so they can use photosynthesis to make food; other organisms eat them and get their food that way. They are at the bottom of the food chain. Many algae are unicellular, some are multicellular, and others live in colonies. They produce oxygen that is needed for all other life forms on earth. Without algae there would not be enough oxygen on earth.They do not cause diseases in humans, but they can be a nuisance in aquariums and swimming pools. Algae are mainly classified by their colors from their pigment composition.

GREEN ALGAE

Ancient green algae most likely gave rise to the first plants and their chloroplasts are very similar. Chloroplasts are the organelles that contain chlorophyll (a green pigment) and use sunlight to make food. Most algae are found in fresh water as well as marine water, but some species of green algae have even adapted to snow in our found in high altitude glaciers where its pigments produce an effect known as “watermelon snow”.

RED ALGAE

Red algae also contain the green colored chlorophyll but it also contains a red pigment which masks it, so it appears red. Red algae are the most abundant large algae in warm tropical oceans. The largest are included in the informal designation “seaweeds” although they are not as big as the giant brown kelps.

GOLDEN ALGAE

Golden algae have two flagella near one end of the cell which they use for motility. Some species can form resistant cysts that can survive for decades when environmental conditions are poor.

BROWN ALGAE

Brown algae are multicellular and are the largest type of algae. It is mostly found in cool bodies of saltwater. They are the most common species of seaweeds. They are the most complex of all algae; some even have specialized tissues and organs that resemble those in plants. Seaweed is an important commodity for humans. Many types of seaweed are harvested for food, including for soups, crispy sheets, and wraps for sushi. Seaweed is also used to pick in many processed foods such as pudding, ice cream, and salad dressing.

DIATOMS

Diatoms are unicellular, photosynthetic algae. They are unique because their cell walls are made of a glass-like substance called silica. They come in geometric shapes that overlap like a shoe box with its lid. This provides an effective protection from the crushing jaws of filter feeder fish. Researchers have found that diatoms can stand pressures of up to 1.4 million kg per square meter, equal to the pressure under each leg of a table supporting an elephant! When a diatom dies, it leaves behind its fossilized walls. These fossils, combined with soil sediments, are known as diatomaceous earth, which is sold as bags of soil for houseplants because it provides good drainage and aeration. They are also used for filters and as a grinding and polishing agent.

DINOFLAGELLATESare single celled algae that are motile and are shaped like an acorn with armored plates. These algaeoften cause red tides and massive fish kills.

BLUE-GREEN “ALGAE”

What is called “blue-green algae” is actually not a true alga, but a bacterium called cyanobacteria, which contains chlorophyll and is able to make its own food. However, it can turn lakes and aquariums an unsightly green color, and is a common nuisance. It is beneficial to other marine plants because it recycles nutrients such as nitrogen, but it can be a problem because it contributes to algae blooms, especially during warm weather. Some species produce hydrogen and are being investigated as a possible alternative source of energy. Other species are dangerous to animals and humans because they produce toxins that cause liver cancer.

NUISANCE ALGAE

Algae become a nuisance when it grows in swimming pools, aquariums, and blooms to excess in oceans. In swimming pools, it can be easily treated with chlorine. However, chlorine is toxic to fish, so an algaecide must be used to get rid of the algae without harming the fish. A typical algaecide works by removing phosphate from the water. Without phosphate, algae are not able to produce energy, so they die off. The standard chemical used for this is copper sulfate; when it is exposed to phosphate, it becomes copper phosphate, which sinks to the ground in a solid form. However, in deeper waters with a low oxygen content, the copper can disengage from the phosphate and become toxic to the environment. For this reason, the use of copper sulfate is restricted by the Environmental Protection Agency in lakes. However, it is still available for commercial use in aquariums.

ALGAE BLOOMS

Algal blooms are the result of an excess of nutrients (particularly phosphorus and nitrogen) into waters and higher concentrations of these nutrients in water cause increased growth of algae and green plants. As more algae and plants grow, others die. This dead organic matter becomes food for bacteria that decompose it. With more food available, the bacteria increase in number and use up the dissolved oxygen in the water. When the dissolved oxygen content decreases, many fish and aquatic insects cannot survive. This results in a dead zone. Algae blooms especially occur during periods of warm weather, so global warming is resulting in more algae blooms with subsequent dead zones that kill off the shellfish there.

Algal blooms may also be of concern as some species of algae produce neurotoxins which may have severe biological impacts on wildlife. Algal blooms sometimes occur in drinking water supplies. In such cases, toxins from the bloom can survive standard water purifying treatments.

Dead zones are low-oxygen areas in the world's oceans; there are 146 dead zones in the world oceans where marine life cannot be supported due to depleted oxygen levels. Some of these were as small as a square kilometer, but the largest dead zone covered 70,000 square kilometers. In the US, the East Coast's Chesapeake Bay has a large dead zone.

Off the coast of Cape Perpetua, Oregon, there is also a huge dead zone. This dead zone is unique in that it only exists during the summer, perhaps due to seasonal wind patterns.

Currently the most notorious dead zone is a 20,000 square kilometer region in the Gulf of Mexico, where the Mississippi River dumps high-nutrient runoff from its vast drainage basin, affecting important shrimp fishing grounds. Low oxygen levels have led to reproductive problems in fish involving decreased size of reproductive organs, low egg counts and lack of spawning.

Dead zones are not irreversible. The Black Sea dead zone, previously the largest dead zone in the world, largely disappeared between 1991 and 2001 after fertilizers became too costly to use following the collapse of the Soviet. Fishing has again become a major economic activity in the region.

While the Black Sea "cleanup" was largely unintentional and involved a drop in hard-to-control fertilizer usage, the U.N. has advocated other cleanups by reducing large industrial emissions. From 1985-2000, the North Sea dead zone had nitrogen reduced by 37% when policy efforts by countries on the Rhine River reduced sewage and industrial emissions of nitrogen into the water. During this time, the US also passed a law prohibiting phosphates in laudnry detergents, and this has helped reduce the algal blooms in our country.

PROTOZOA

Protozoa are larger than bacteria; many bacteria can fit into a protozoon.They absorb or ingest organic chemicals. They are classified according to their motility(movement): by pseudopods (false foot), cilia (hairs) or flagella (tail).

MEDICALLY IMPORTANT PROTOZOAS

Archaezoa

Giardia lambia(disease is called giardiasis)

Trichomonas vaginalis(disease is also called trichomonas)

Amoebas

Entamoeba histolytica(disease is called ameobiasis)

Balentidium coli(disease is called ameobiasis)

Apicomplexa

Plasmodium (disease is called malaria)

Toxoplasma (disease is called Toxoplasmosis)

Trypanosomes

Trypanosoma brucii (disease is called African Sleeping Sickness)

Trypanosoma cruzi (disease is called American Trypanosomiasis or Chaga’s Disease)

Leishmaniasis

Leishmania(disease is called Leishmaniasis)

1. ARCHAEZOA (archae = old; these are closely related to the first protozoa). They have no mitochondria; they have multiple flagella.

A.Giardia lambia: Giardia is common worldwide, including Southern California, from drinking untreated outdoor water. After a few days you develop persistent, chronic diarrhea (dysentery). The organism looks like a happy face; what looks like two eyes are nuclei.

B.Trichomonas vaginalis: A common sexually transmitted disease which is without symptoms in males. It causes severe itchiness in females and is easily treated with antibiotics.

2. AMEOBAS : These organisms look like jelly; theymove by pseudopods to get food.Pseudopods are characteristic of amoebas. Two main types of amoebas that cause disease in humans; both diseases are called ameobiasis.

A.Entamoeba histolytica: This is a global disease that any traveler can get. As soon as you cross the border into Mexico, you are exposed to it. This organism likes to eat red blood cells. In a fresh diarrheal specimen, you can see red blood cells (RBCs) in the cytoplasm of the amoeba.

B. Balentidium coli: The animal reservoir is the pig. It is found world-wide, wherever humans and pigs live nearby each other. The cyst form has a thick wall to protect it from stomach acid. It enters the human (and dogs) by ingestion of fecal contaminants on food, water, and hands. Once in the colon, it reproduces in the large intestine, invades the colon wall, and cause ulcerations in the colon. Symptoms include diarrhea and GI discomfort.

MALARIA

This disease kills 2-3 million people a year, mostly young people and teenagers.

200-300 million people are infected each year.

2/3 of malaria cases are in Africa.

Animal vector: anopheles mosquito

Causative agent: Plasmodium

Only female anopheles mosquitoes are the vector. Only the female mosquito has a needle-sharp proboscis (mouth part) that penetrates the skin of the human. They need the blood to nourish their eggs. This is a tropical mosquito found in warm environments. Since global warming is affecting us, we may see an increase in cases of malaria in the US, especially California.

The term “malaria” comes from “mal air”, which means “bad air”. They used to think malaria was cause from the bad air of a foul-smelling swamp. Later it was discovered that the disease was caused by the protozoa inside the mosquito.

The protozoa migrate into the salivary gland of the mosquito, and they are injected into the blood of the human. They immediately go to the liver. This is the only way to get malaria; you can’t get it from a blood transfusion because they only spend a short time in the blood. They go right to the liver quickly. In the liver cells, they form cysts and reproduce. The cyst eventually ruptures and releases the protozoa into the bloodstream, where they enter red blood cells (RBCs). The patient now starts to have symptoms. The RBC eventually ruptures, and this releases a lot of toxins all at once. This is what causes the symptoms of abdominal pain, myalgia (muscle pain), fever, chills, and shivering. It takes about 48-72 hours after this for the protozoa to infect new RBCs and cause them to rupture, setting off a new cycle of symptoms. Thus, these symptoms are regular and recurrent (described by the term “paroxysms”). This disease also results in anemia.

Some of the protozoa are sucked up by another mosquito and transmitted to a new human. Treatment involved the plant product quinine (in the form of Methoquin, Primoquin, etc).Sometimes treatment is prophylactic; you can take it before you go on a trip to Africa to prevent the disease. Some forms of malaria are chronic.

TOXOPLASMOSIS

Causative agent: Toxoplasma

Animal vector: cats (Most warm-blooded animals harbor it, especially cats)

This disease is global (world-wide). People who get infected develop antibodies that can be detected by serological assays (special blood tests). By this means, it has been determined that about 40% of the US population has been infected (serologic positive) for this disease. However, the symptoms are usually subclinical (mild or no symptoms). The exceptions to this are for those who are immunocompromised (HIV, infants, etc).

MODES OF TRANSMISSION

1. Fecal-oral: The cat defecates and releases protozoa cysts. Humans ingest it after cleaning cat litter boxes. It only causes a problem in the fetus of a pregnant woman who cleans the box.
2. Eating meat not fully cooked (tissue cyst). In France, it is common to eat raw meat, so the disease is more common there.
3. Congenital transmission (fetus gets infected when mother gets the disease)

GEOGRAPHIC DISTRIBUTION

France (from eating raw meat)

Central America (lots of stray cats)

United States (pet cat eats a wild bird, pregnant woman cleans cat litter box, especially during first trimester)

This organism prefers nerve tissue, so it travels to the CNS. In the fetus, it causes retinal damage (blindness), brain damage, hydrocephaly, and stillbirths. In other humans, it causes mild symptoms which go away, then white blood cells make antibodies that can be detected. Treatment is needed only for those who are immunocompromised (AIDS patients, etc).

TRYPANOSOMES

Causative agent: Trypanosoma

Diseases:

1. African Trypanosomiasis (African Sleeping Sickness)
2. American Trypanosomiasis (Chaga’s Disease)

AFRICAN TRYPANOSOMIASIS

The biological vector is the tsetse (pronounced “set-see”) fly. The tsetse fly bites a human and injects the protozoas into the skin. This causes a chanchre (pronounced “shanker”), which is an ulcer on the skin. Then it enters the lymph nodes. It is characterized by Winterbottom’s Sign: swelling of the cervical lymph nodes in the head and neck area.

Central nervous system (CNS) symptoms include a shuffling gait (like a stroke victim), slurred speech, and malaise (needing to sleep longer and longer each day). They are also restless at night.

AMERICAN TRYPANOSOMIASIS

This disease is NOT found in Africa.The biological vector is a large bug called the “Kissing Bug”. It is found in warm regions and crowded areas, especially in the cracks of adobe huts. It comes out at night and crawls on a human while they sleep. It prefers the lips because the blood supply is close to the surface. It sucks the blood there, but they don’t transmit the organism this way. When they suck the blood, they also defecate, and the organism is in the feces. When the human wakes up to scratch the itch, feces get into the tiny wound. This is a fecal blood route.

Symptoms include fever, anorexia, swollen lymph nodes, enlarged liver and spleen, and inflammation of the heart, which usually causes death.

LEISHMANIA

Organism: Leishmania

Disease: Leishmaniasis

Geographical Distribution: tropic and subtropic

Biological vector is a sandfly, which is quite small. It is smaller than a fruit fly, but larger than a mosquito.

There are three forms of Leishmaniasis:

1. Cutaneous
2. This is disease only at the site of the bite. This form is seen in Texas, Mexico, Asia, and the Middle East (our Iraq troops are coming down with this form). It manifests as a large, wet sore with raised edges. It looks like a volcano with weepy serum coming out of the center. The wound is not contagious, just the sandfly bite. Dogs can get this disease, too.
3. Mucocutaneous
4. This is disease located in the mucous membranes of the nose and mouth. The most gruesome photos are of this form.
5. Visceral
6. This is the most serious form; known as Kala Azar.
7. It occurs especially in immunocompromised people, especially HIV patients.
8. In this form, the protozoa multiply in white blood cells as well as other organs including the spleen, liver, and lymph nodes. Symptoms fever, weight loss, and a decrease in all types of blood cells: WBC, RBC, and platelets. The treatment is almost as bad as the disease because of the side effects. It is best to catch it early.

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