Workbook Source: MicrobeWorld – Where They Live
What is a Microbe?
Microbes are single-cell organisms. They are so small that millions can fit
into the eye of a needle. They are the oldest form of life on Earth. Microbe
fossils date back more than 3.5 billion years.
Without microbes, we couldn’t eat or breathe. Without us, they’d probably
be just fine.
Understanding microbes is necessary to understanding the past and the future of our planet and ourselves.
Microbes (my-crobez) are everywhere. There are more of them on a person's hand than there are people on
Earth! Microbes are in the air we breathe, the ground we walk on, the food we eat—they're even inside us!
We couldn't digest food without them—animals couldn't, either. Without microbes, plants couldn't grow,
garbage wouldn't decay, and there would be a lot less oxygen to breathe.
In fact, without these invisible companions, our planet wouldn't survive, as we know it!
Our Challenge: How are we going to solve the case of what a microbe is when they're so
small they're invisible to us?
Microbe is a term for tiny creatures that are too small to be seen with the unaided eye. Microbes include
bacteria (back-tear-ee-uh), Archae (are-key-uh), fungi (fun-guy) and protists (pro-tists). Protists include
primitive algae (al-gee), amoebas (ah-me-buhs), slime molds and protozoa (pro-toe-zoh-uh).
To solve the case of what a microbe is, we have to use tools such as high-power microscopes. Let's zoom in
on some microbes and see what a few of these strange creatures look like.
As you can see, microbes come in many varieties. They may live as individuals or cluster together in
communities.
So how small are microbes? Well, let's say we could enlarge an average
virus, the smallest of all microbes, to the size of a baseball. An average
bacterium would then be the size of the pitcher's mound.
And just one of the millions of cells that make up your body would be the size of the ballpark!
Where They Live
Our Challenge: Name at least three places microbes live. Can you think of any places that
microbes might not live?
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Microbiologists have found microbes living just about everywhere: in the soil, water,
and air; in animals, plants, rocks, and even us!
Your body is home to trillions of microbes. Run your tongue over your teeth—you're
licking thousands of microbes that normally live on your teeth, like those pictured here.
Millions of them live on your tongue, too. A large part of "you" (that is, the mass of
your body) is actually something else: bacteria and fungi. Isn't that a weird thought?
Pick up a fistful of garden soil and you're holding hundreds if not thousands of different
kinds of microbe in your hand. A single teaspoon of that soil contains over
1,000,000,000 bacteria, about 120,000 fungi and 25,000 algae.
Microbes have been around for billions of years. They are able to adapt to the ever-changing environment.
They can find a home anywhere and some of them live in places where we once thought NOTHING could
survive.
Scientists have discovered microbes living in the boiling waters of hot springs in Yellowstone National Park.
These microbes "eat" hydrogen gas and sulfur and "breathe" hydrogen sulfide (a gas that smells like rotten
eggs).
Other heat-loving microbes live in volcanic cracks miles under the ocean
surface where there is no light and the water is a mixture of poisonous arsenic,
sulphur and other nasty chemicals. The little blobs shown in this photo are
bacteria that live on mussel shells around a volcanic vent called the Galapagos
Vent.
Other microbes live in the permanently frozen ice of Antarctica.
Fungi and Bacteria
As land plants were evolving, they ran into a few obstacles. Soil can sometimes prove a nutrient-poor and
unfriendly environment. To grow, plants need nitrogen to make proteins. They can’t change nitrogen in the
air into a form their cells can use.
To overcome these obstacles, early plants struck deals with bacteria and fungi.
Some early bacteria developed the chemical tools to collect nitrogen from the air.
They change it into forms such as ammonia and nitrate. This is called fixing
nitrogen. The catch is that they need enough energy to power these changes.
Plants produce large amounts of carbohydrates (car-bow-high-drates) through
photosynthesis (photo-sin-thuh-sis). Ammonia and nitrate are perfect proteinbuilding nitrogen forms for plants.
A group of creative plants called the legumes (beans, peas, clover, and alfalfa)
entered into an agreement with nitrogen-fixing bacteria called Rhizobium.
The bacteria moved into the plants’ roots. The formed bumps on the roots called
nodules. Nodules supply the fixed nitrogen plants need. In exchange, the plants
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supply the bacteria with the carbohydrates they need. Because Rhizobia can still live freely in the soil, plants
are more dependent upon them than the microbes are on plants.
Animals need nitrogen to make proteins. We humans get our nitrogen by eating
plants (or by eating animals that eat plants).
Another partnership teams plants with soil-dwelling fungi called mycorrhizae (mycore-high-zay). Almost all plants from flowers to towering trees have partner
mycorrhizae (my-core-high-zay).
Some species of mycorrhizae (my-core-high-zay) cover the surface of plants’ root hairs. Others settle down
inside the plant roots. The fungi act as extensions of the plants’ roots, increasing the surface space of their
nutrient-absorbing network.
Mycorrhizae (my-core-high-zay) increase the amount of water and food a plant can use. In exchange, the
plants provide the fungi energy in the form of carbohydrates.
This partnership enables both plants and fungi to survive in nutrient-poor places where they otherwise might
die.
Ant Farmers and Gardens of Fungi
It’s not clear how and why some early species of ant first took up
fungus farming. Scientists have determined by genetic testing that it
happened about 50 million years ago.
Today, several species of ant (including the famed leaf-cutters of
Central and South America) tend and nurture gardens of fungi in
underground nests.
Ants can’t digest leaves and stem. So, they cut them up and feed
them to the fungi. The fungi break down cellulose (the tough fibrous
material in plant tissues), making nutrients available to the ants.
The ants dig nests and build safe chambers for their fungal gardens. They clean off garbage and parasites
from the fungi. They produce special antibiotics in their bodies to kill organisms that might attack their
crops.
In return, the fungi produce bumps at the tips of their hyphae (high-fay) (long strings of fungal cells). These
bumps are rich in proteins, sugars and other nutrients. The ants dine on these nutritious bumps.
The fungi are guaranteed a large food supply and a stable, nurturing environment in which to live.
The fungi rely upon the ants for reproduction. Before new queen ants fly off to mate and found their own
colonies, they tuck a bit of fungus in their mandibles to start their new gardens. The fungi growing in
virtually every leaf-cutter garden are actually clones of the same fungus farmed by ants 25 million years ago.
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Archaea (are-kay)
There are different types of Archaea. These include:
 Methanogens (meth-an-oh-jins) — Archaeans that produce
methane gas as a waste product of their "digestion," or
process of making energy.
 Halophiles (hal-oh-files) — those Archaeans that live in
salty environments.
 Thermophiles (ther-mo-files) — the Archaeans that live at
extremely hot temperatures.
 Psychrophiles (sigh-crow-files) — those that live at
unusually cold temperatures.
Archaea look and act a lot like bacteria. Until the late 1970s, scientists
assumed they were a kind of “weird” bacteria.
Microbiologist Carl Woese devised a creative way of comparing genetic
information. Tests showed that they could not rightly be called bacteria.
Their genetic recipe is too different.
Woese decided they deserved their own kingdom. He named this
kingdom Archaea.
How They Are Different
Many Archaea have tough outer cell walls. These walls are different from those found in bacteria. Drugs
that slow or kill bacteria have no effect on Archaea.
Classification
Archaeans are single-celled creatures. They are Prokaryotes (pro-carry-oats).
Prokaryotes' do not have a nucleus. Bacteria and Archaea are the only prokaryotes.
While Archaeans resemble bacteria and have some genes that are similar to bacterial
genes, they also contain other genes that are more like what you'd find in eukaryotes
(you-carry-oats). Furthermore, they have some genes that aren't like any found in
anything else.
Early Origins
Archaeans appeared on Earth billions of years ago. Archaea and bacteria developed separately from a
common ancestor nearly 4 billion years ago. Historically, Archaeans are more closely related to humans than
they are to bacteria.
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Archaea of Note
 Lobus fulgidus is a sulfur-reducer that can sour oil wells.
 Halobacteria are salt-loving microbes that give a pink tinge to salt-water evaporation ponds, the
Dead Sea, and salted fish.
 Pyrolobus fumarii led scientists to extend the upper temperature limit for life to 113 degrees Celsius
(235.4 degrees Fahrenheit).
 Pyrococcus furiosis is the source of an extra-stable enzyme that can endure many cycles in the
process of PCR, the method behind gene sequencing and DNA fingerprinting.
 Sulfolobus acidocaldarius is used to filter copper and iron from rocks.
Bacteria
Many of us know bacteria only as “germs,” invisible creatures that can make us sick. Few know that many
bacteria only live with us all the time. They help us do an amazing number of useful things. For example,
they make vitamins, break down some garbage, and even maintain our atmosphere.
Bacteria consist of only a single cell. Don’t let their small size and plainness fool you. They're a complex
and fascinating group of creatures. They "eat" everything from sugar and starch to sunlight, sulfur, and iron.
Classifications: What Difference Does it Make?
Does a bacterium’s cell wall, shape, way of moving, and environment really matter?
Yes! The more we know about bacteria, the more we are able to figure out how to make microbes work for
us or stop dangerous ones from causing serious harm.
What They Look Like
There are thousands of species of bacteria. All bacteria are one of three different shapes. Some are rod- or
stick-shaped and called bacilli (buh-sill-eye). Others are shaped like little balls and called cocci (cox-eye).
Others are spiral in shape.
Some bacterial cells exist as individuals. Others cluster together to form pairs, chains, squares or other
groupings.
The human body consists of millions of different cells. A bacterium
consists of a single cell.
A bacterium’s genetic information is contained in a single DNA molecule.
The cell is full of a jelly-like substance called cytoplasm. Cell parts are
surrounded by a flexible membrane. That is surrounded by a tough, rigid
cell wall. A few species, such as the mycoplasmas, don’t have cell walls.
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Even though bacteria have only one cell each, they come in a wide range of shapes, sizes, and colors.
Size
Sizes vary from 1 millimeter in diameter at the largest end of the scale to 20 nanometers in length at the
smallest. The largest bacteria found so far can actually be seen without the use of a microscope
(Thiomargarita namibiensis and Epulopiscium fischelsoni). The smallest known bacteria are so tiny that they
were once thought to be viruses (Mycoplasmas).
Do bacteria actually have colors?
Some bacteria do have natural colors. Certain species contain pigments, such as various chlorophylls, that
make them naturally green, yellow, orange, or brown. Colonies of millions of bacteria may appear pink,
yellowish, or white.
Many of the vividly colored images you see have been color enhanced or stained with dyes for better
viewing under a microscope.
Where They Are Found
Bacteria can be found almost everywhere. They are in the air, the soil, and water, and in and on plants and
animals, including us. A single teaspoon of topsoil contains about a billion bacterial cells (and about 120,000
fungal cells and some 25,000 algal cells). The human mouth is home to more than 500 species of bacteria.
Bacteria live on or in just about every material and environment on Earth from soil to water to air and from
your house to arctic ice to volcanic vents. Each square centimeter of your skin averages about 100,000
bacteria. A single teaspoon of topsoil contains more than a billion (1,000,000,000) bacteria
How They Move
Some bacteria produce thick coats of slime and ‘glide’ about. Some stick out thin, rigid spikes called
fimbriae (fim-bree-a) to help hold them to surfaces. Some contain little particles of minerals that orient with
the planet’s magnetic fields to help the bacteria figure out whether they’re swimming up or down.
Some bacteria move about their environment by
means of long, whip-like structures called flagella.
They rotate their flagella like tiny outboard motors
propel themselves through liquid environments.
They may also reverse the direction in which their
flagella rotate so that they tumble about in one
place.
to
What They Eat
Some bacteria are photosynthetic (foe-toe-sin-theh-tick). They can make their own
food from sunlight, just like plants. Also like plants, they give off oxygen. Other
bacteria absorb food from the material they live on or in. Some of these bacteria can
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live off unusual "foods" such as iron or sulfur. The microbes that live in your gut absorb nutrients from the
digested food you've eaten.
Notable Bacteria
 Bacillus anthracis causes anthrax, a deadly disease in cattle and a potential bioweapon against
humans
 Brucella abortus causes breeding losses in livestock.
 Cyanobacteria (formerly known as blue-green algae) live in water, where they produce large
amounts of the oxygen we breathe.
 Escherichia coli (E. coli) lives in the gut, where it helps digest food and produces Vitamin K.
The "bad" strain of E. coli O157:H7 causes severe foodborne sickness.
 Lactobacillus bulgaricus helps turn milk into cheese, yogurt, and other dairy products.
 Bacterium tuberculosism Mycoba causes tuberculosis, a major killer from the past that has
recently resurged with the advent of AIDS.
 Rhizobia convert free nitrogen into a form that the plants can use in order to grow.
 Staphylococcus (staph) can cause serious infections and is one of the most drug-resistant
bacteria.
 Streptococcus pneumoniae causes strep throat, meningitis, and pneumonia.
 Streptomyces griseus makes the antibiotic streptomycin.
 Thermus aquaticus is a heat-loving bacterium from which scientists got the enzyme Taq
polymerase that makes routine DNA fingerprinting and gene sequencing possible.
Fungi
Fungi range in size from the single-celled organism we know as yeast to the largest known living organism
on Earth — a 3.5-mile-wide mushroom.
Dubbed “the humongous fungus,” this honey mushroom (Armillaria ostoyae) covers some 2,200 acres in
Oregon’s Malheur National Forest.
The only above-ground signs of the humongous fungus
are patches of dead trees and the mushrooms that form
at the base of infected trees. (See image on left.)
It started out 2,400 years ago as a single spore invisible
to the naked eye, then grew to gargantuan proportions
by intertwining threads of cells called hyphae.
Under a microscope, hyphae look like a tangled mass of threads or tiny
plant roots.
If mushrooms and other fungi can get so huge, why mention them on a
site about microorganisms?
Visible fungi such as mushrooms are multicellular entities, but their
cells are closely connected in a way unlike that of other multicellular
organisms.
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Plant and animal cells are entirely separated from one another by cell walls (in plants) and cell membranes
(in animals). The dividers between fungal cells, however, often have openings that allow proteins, fluids and
even nuclei to flow from one cell to another.
Classifications
Fungi are eukaryotic (you-carry-ah-tick) organisms—their DNA is enclosed in a nucleus. Many of them
may look plant-like, but fungi do not make their own food from sunlight as plants do.
Friendly Fungi
Some fungi are quite useful to us. We use several kinds to make antibiotics to fight bacterial infections.
These antibiotics are based on natural compounds the fungi produce to compete against bacteria for nutrients
and space. We use Saccharomyces cerevisiae (sack-air-oh-my-seas sair-uh-vis-ee-ay), baker's yeast, to make
bread rise. Fungi break down dead plants and animals and keep the world tidier. We're exploring ways to use
natural fungal enemies of insect pests to get rid of these bugs.
Fungal Enemies
There are some nasty fungi that cause diseases in plants, animals and people. One of the most famous
is Phytophthora infestans (fie-tof-thor-uh in-fes-tuhns), which caused the Great Potato Famine in Ireland in
the mid-1800s that resulted in a million deaths. Fungi ruin about a quarter to half of harvested fruits and
vegetables annually.
What They Look Like
Fungi are eukaryotic organisms. This means their cells have a nucleus. (Bacteria and Archaea do not have a
nucleus. This makes them prokaryotic organisms.) Fungi cannot make their own food. They eat organic
matter like rotting leaves, wood, and other debris, or upon the tissues of living plants and animals.
Fungi, along with bacteria, are the planet’s major decomposers and recyclers. Fungi may seem like a
nuisance when they dine in your fruit bowl or refrigerator. Their ability to degrade some of the toughest
organic materials, including tree wood and dead insects, means that our planet is not cluttered with a mass of
debris.
Fungi dine at home, eating whatever they’re growing on. Fungi break
down food sources, such as animal corpses and tree stumps, into
smaller parts they can absorb.
Fungi include single-celled creatures that exist individually—the
yeasts—and multicellular bunches, such as molds or mushrooms. Yeast
cells look like little round or oval blobs under a microscope. They're
too tiny to see as individuals. You can see large clusters of them as a
white powdery coating on fruits and leaves.
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Molds have long thread-like, strands of cells called hyphae (high-fay). Hyphae give mold their fuzzy
appearance. They also form the fleshy body, or mushroom, that some species grow. Hyphae are like a tube.
Your cells, on the other hand, are completely walled off from each other and the cell fluid, or cytoplasm
(sigh-toe-plazm), inside doesn't mingle between cells.
How They Move
Fungi can’t move on their own. They can spread by forming reproductive spores that are
carried on wind and rain or by growing and extending their hyphae. Remember that
hyphae are chains of fungal cells.
Hyphae grow as new cells form at the tips. They make longer and branching chains of
cells. It takes a lot to stop them, too. Hyphae are tough enough to punch through plant
cell walls and the hard exoskeletons of insects.
Where They Are Found
Fungi can be found in rising bread, moldy bread, and old food in the refrigerator, and on forest floors. Most
decompose non-living things. Some damage crops and plants. A few cause problems in people.
If you’ve ever baked bread, you’re probably familiar with the only fungi that are truly a single-celled
organism: yeast.
Fungi usually grow best in environments that are slightly acidic. They can grow on things with very low
moisture. Fungi live in the soil and on your body, in your house and on plants and animals, in freshwater and
seawater. A single teaspoon of topsoil contains about 120,000 fungi.
What They Eat
Fungi absorb nutrients from living or dead organic matter (plant or animal stuff) on which they grow. They
absorb simple, easily dissolved nutrients through their cell walls. They give off special digestive enzymes to
break down food into forms that they can absorb.
Hunters and Grazers
Most fungi can best be described as grazers, but a few are active hunters. Hunter fungi prey on tiny protozoa
and worm-like creatures called nematodes. Some produce a sticky substance on their hyphae, which then act
like flypaper, trapping passing prey.
One species sets snares made out of loops formed by its hyphae. When a nematode contacts the loops, the
movement triggers the fungal cells to swell with fluid. Fluid tightens the loop like a noose around the
nematode. Other hyphae then grow toward the trapped prey. They punch through its body where they begin
absorbing its fluids.
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Let’s Make a Deal
Other fungi get other creatures to feed them. For example, mycorrhizae (my-core-high-zay) work with many
species of plants. The plants provide the fungi the food it needs and a place for their roots. The fungi help the
plants absorb essential nutrients.
Lichens team up with green algae so they grow in places that neither could grow alone. Algae or bacteria
make food eaten by the fungal cells. The fungi fasten the lichen in place and protect the algae or bacteria.
Fungi of Note
by Chris Condayan on March 11, 2009
 Armillaria ostoyae (a.k.a. the honey mushroom) can grow to gargantuan proportions, like the
“humongous fungus” that covers 2,200 acres in Oregon’s Malheur National Forest.
 Ashbya gossypii is a source of vitamins, such as riboflavin.
 Aspergillus flavus produces a poison called aflatoxin on peanuts and other crops that can make
people who eat these foods sick.
 Aspergillus niger makes enzymes used in laundry detergents and many other products, and for
tanning leather.
 Beauveria bassiana is used as a pesticide to control nuisance insects.
 Fusarium is a group of fungi that cause diseases in a wide range of plants.
 Helminthosporium oryzae causes disease in rice and led to the Bengal famine of 1942.
 Histoplasma capsulatum causes the lung disease histoplasmosis.
 Mucor circinelloides is a filamentous fungus that produces long, thread-like filaments called hyphae
that can grow to amazing lengths. M. circinelloides is used in food production to convert fatty acids
into natural flavoring compounds.
 Penicillium notatum is the mold that launched the development of antibiotics and gave us penicillin.
 Phanerochaete chrysosporium degrades various hazardous waste compounds.
 Puccinia chondrillina is used as a mycoherbicide to control weeds.
 Saccharomyces cerevisiae (a.k.a. baker’s yeast) makes bread rise and ferments grapes and grains.
 Serpula lacrymans causes dry rot of wood.
 Stachybotrys chartarum is a type of toxin-producing fungi commonly implicated in “sick building”
syndrome.
 Tolypocladium inflatum gives us cyclosporine, the first drug to prevent organ rejection in transplant
patients.
 Trichophyton rubrum causes athlete’s foot.
Protista
Algae, Protozoa, Slime Molds, and Water Molds
Protists are eukaryotic creatures (you-carry-ah-tick), meaning they have a nucleus. They’re not plants,
animals or fungi, but they act enough like them that scientists believe protists paved the way for the
evolution of early plants, animals, and fungi. Protists fall into four general subgroups: unicellular algae,
protozoa, slime molds, and water molds.
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Green Algae
The most clearly plant-like algae, this species gets its namesake hue from high levels of chlorophyll. Their
cell walls are made up of cellulose. This also makes up the cell walls in plants. They store the food they
make through photosynthesis as starches. They grow in large groups. Algae can form visible layers of slick,
green scum on the surfaces and sides of ponds, puddles or damp soil.
Fossil records suggest that the first green algae originated 500 to 600 million years ago. Early algae probably
gave rise to multicellular plants.
Dinoflagellates
Dinoflagellates have long whip-like structures called flagella. This lets them turn,
move and spin about through the water. About 90% of these algae dwell in the
ocean.
Some species glow in the dark. These species contain a compound called luciferin
(the same compound found in fireflies). The glow increases if the algae cells are
disturbed, as when a ship churns through the water.
About half the species of dinoflagellates make their own food. The other half are predators that attack
bacteria, algae, and even fish.
Dinoflagellate poisons can concentrate in the bodies of shellfish and fish that eat the algal cells. This can
cause people who eat these seafoods to become ill. It could lead to death.
“Red tides” occur when huge blooms of trillions of dinoflagellates are triggered by an upwelling of nutrients
from the water’s depths during warmer seasons. The population of dinoflagellates can jump to more than 20
million cells per liter of seawater along some coasts during these blooms, turning the water a reddish hue.
Diatoms
Because they depend on sunlight, diatoms generally live in the upper 650 feet of
oceans and bodies of fresh water. These algae look more like flying saucers, tiny
canoes or cigars, lobed leaves, the undersides of mushroom caps, striated ribbons, or
filigreed Christmas ornaments. Whatever their shape, all diatoms have shell-like,
brittle cell walls made out of silica (glass) and pectin. The walls are two interlocking
halves or shells that fit together like a pillbox.
Some species of diatoms simply float in the water currents near the surface. Others
attach themselves to larger floating objects or to the sea floor. When diatoms die, they
slowly sink to the sea floor. The buildup of trillions of these shells forms a crumbly
white sediment known as diatomaceous earth or diatomite, which is used in
manufacturing pool filters and abrasives, including toothpaste.
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Algae
Algae also play an important role as the base for the marine food chain. All higher marine life forms depend
either directly or indirectly on microscopic algae. Most unicellular algae live in water. Some dwell in moist
soil. Others join with fungi to form lichens.
Over 50% of our oxygen is made by algae. Algae are plant-like microorganisms. Algae cells contain lightabsorbing chloroplasts and produce oxygen through photosynthesis.
When you think of algae, you probably think of seaweed or the green, slimy stuff that forms on the walls of
swimming pools. Here we'll focus on the microscopic algae.
Algae are found in fresh and salt water across the globe. They can also grow on rocks and trees and in soil
when enough moisture is available.
Most algae are able to make energy from sunlight. At some stages of their lives, some algae get their
nutrients from other living things. Some dinoflagellates make toxic substances that stun passing fish and
cause bleeding sores. The Piesteria then feed on the fish blood and fluids.
Protozoa
The name protozoon means “first animals.” Protozoa play a key role in maintaining the balance of bacterial,
algal, and other microbial life. They also are an important food source for larger creatures and the basis of
many food chains.
Protozoa have been found in almost every kind of soil environment from peat bogs to arid desert sands. They
live in the deep sea as well as near the surface of waters. They can be found in frigid Arctic and Antarctic
waters.
Some species of protozoa are part of the normal microbial flora of animals. They live in the guts of insects
and mammals. They help to break down complex food particles into simpler molecules. A very small
number of species cause disease in people, including one, which causes malaria.
The four main subgroups of protozoa are the ciliates, the flagellates, the sarcodina, and the apicomplexans.
Some protozoa absorb food through their cell membranes. Others, like the amoebas (ah-me-buhs), surround
food and engulf it. Others have openings called mouth pores into which they sweep food.
All protozoa digest their food in stomach-like compartments called vacuoles (vac-you-ohls). As they chow
down, they make and give off nitrogen, which is an element that plants and other higher creatures can use.
Protozoa range in size from 1/5,000 to 1/50 of an inch. They can be classified into three general groups based
on their shape.
One group is the Ciliates (silly-ates), which are generally the largest
protozoa. They have hair-like projections called cilia (silly-uh). They eat
the other two types of protozoa as well as bacteria.
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The second group is the Amoebae (ah-me-bee). There are the testate amoebae, which
have a shell-like covering. There are also naked amoebae, which don't have this covering.
Finally, the third group is the Flagellates (flah-geh-lets). They are
generally the smallest of the protozoa. Flagellates have one or
several long, whip-like projections called flagella poking out of their
cells.
To hunt, protozoa have to be able to move about. Amoebas ooze about by extending parts of their cells as
pseudopods (sue-doh-pods) or "false feet." Amoebae have fluid cell membranes or coverings that they can
stretch out, bend and curve. Many ciliates swim along by beating their cilia in a rhythmic pattern, like so
many tiny oars. Flagellates swim by waving their flagella, using them much like a fish uses its tail push itself
through water.
Some protozoa prefer to latch themselves in one place. For example, a ciliate
called Vorticella (vor-tih-chell-uh) attaches to a spot on a long, springy stalk. It creates a
mini whirlpool around its mouth pore by beating the cilia ringing its top end so that food
particles are sucked in. Whenever anything too big to be eaten hits a Vorticella, it springs
back out of the way by rapidly coiling up its stalk.
The majority of protozoa do us no harm. But, there are a few that cause disease. One type of amoeba can live
in human intestines. It feeds on red blood cells and causes a disease known as dysentery (dis-in-tear-ee). The
parasitic protozoan Cryptosporidium parvum (cryp-toe-spore-id-ee-um par-vum) sickened around 400,000
people in Milwaukee in 1993 when it got into the tap water. Perhaps the best-known protozoal menace
is Plasmodium (plaz-mo-dee-um), the parasite that causes malaria. This terrible disease leads to about
800,000 deaths each year worldwide.
Slime Molds
In 1973, a Dallas resident went out to the backyard only to stumble upon a reddish, jelly-like mass pulsating
in the grass. News reports on the discovery claimed that a “new life form” had been found. Scientists called
to the scene identified the mass as a large plasmodial slime mold.
Slime molds spend most of their lives alone. During food shortages, they swarm and combine into an
enormous single cell. Slime molds are like both fungi and animals. The joint structure produces a slimy
covering. It is called a slug because it so resembles the slug you see gliding across sidewalks. Slime molds
were once considered fungi. But, unlike fungi, they can move.
There are two kinds of slime molds. Plasmodial slime molds (the most common kind) share one big cell wall
that surrounds thousands or millions of nuclei. Cellular slime molds also produce spores, but these germinate
into amoeba-like cells. The cells happily go their individual ways, as long as food and water are available.
When nutrients and moisture are scarce, individual cells send out a chemical beacon to attract other cells of
the same species. The cells join up to form a mass that looks and acts like a slug to take them to a more
favorable location.
Cells in cellular slime molds retain their individual cell walls when they form a mass, so the visible slug is
actually a collection of hundreds of thousands of individual cells joined together. Slime molds eat decaying
vegetation, bacteria, fungi, and even other slime molds. They are most commonly found in forests.
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Protista of Note
 Green algae grow in masses that form slick, green scum on pond surfaces. Its ancestors from 500
million years ago probably gave rise to today's multicellular plants.
 Plasmodium vivax, the parasite that causes malaria, lives part of its life cycle in mosquitoes and
the other part in human hosts where it infects and ruptures blood cells in large numbers.
 Phytophthora infestans is the water mold responsible for the Great Potato Famine that killed
nearly a million people in Ireland in 1846–1847.
Why is Handwashing Important?
You carry millions of microbes on your hands. Most are harmless, but you can pick up some
that cause illnesses, such as colds, flu, and diarrhea. When we forget to wash our hands,
or don't wash them properly, we can spread these germs to other people, or give them to
ourselves by touching our eyes, mouths, noses or cuts on our bodies.
We can also pick up germs from objects, such as doorknobs and stair railings, touched
by other people who aren't good handwashers. Think about all the things you touch each
day and how many people may have touched them before you.
Handwashing with warm water and soap can greatly reduce the chances of spreading or
getting germs. The mechanical action of scrubbing loosens up the dirt and microbes on our
hands and the soap picks them up and binds to them so that the water can wash them away.
When Should I Wash?
Before you…
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Prepare or eat food
Treat a cut or wound
Tend to someone who's sick
Put in or take out contact lenses
Do any kind of activity that involves putting your fingers in or near
your mouth, eyes, etc.
Microbes on a cutting board.
After you…
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Go to the bathroom
Handle uncooked foods, especially raw meat
Eat
Blow your nose, cough or sneeze
Handle garbage
Tend to someone who's sick
Change a diaper
Play with or touch a pet, especially reptiles and exotic animals
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Did You Know?
Everyday Roles
Some people think it would be great if scientists could wipe out all the microbial bugs! Should we do it?
Why or why not? It's true that some microbes cause health problems such as strep throat, chickenpox and
the common cold. Unfortunately, because a small number of microbes cause disease, all microbes have a bad
rap. It seems only a few bad microbes get almost all the press. You just don't hear as much about all the
many GOOD things microbes do every day.
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Lactobacillus sanfranciso – This bacterium gives sourdough its unique flavor by producing lots of
tangy lactic acid.
Bacillus thruingiensis – Also known as “Bt,” this common soil bacterium acts as a natural pest killer
in gardens and on crops.
Propionibacterium freudenreichil – This bacterium produces carbon dioxide gas bubbles that burst
in ripening cheese leaving the holes in Swiss cheese.
Saccharomyces cerevisiae – Saccharomyces is also known as Baker’s Yeast because it is used to
make bread rise. This fungus also breaks down the natural sugars in grains or other starchy
ingredients into carbon dioxide and ethanol (alcohol).
Methanotroph – Eats methane gas to clean up hazardous waste dumps and landfills. These methanemunching bacteria make an enzyme that can break down more than 250 nasty pollutants into
harmless molecules. By piping methane into the soil, we can increase growth of the methanotrophs
that normally live in the polluted soil. More methanotrophs means faster pollution break-up.
Acetobacter – Modifies glucose, making vitamin C as a by-product.
Streptomyces – A soil bacteria that makes streptomycin, an anti-biotic used to treat infections. Fungi
and bacteria produce powerful anti-biotics like penicillin and tetracycline. These are drugs that are
used to fight off nasty bacteria that cause strep throat, ear infections, diarrhea, and other discomforts.
Aspergillus oryzae & Kluyveromyces lactis – These fungi produce lactase, an enzyme that breaks
down lactose, enabling people who are lactose intolerant to drink milk.
Arbuscular mycorrhizas – Part of a soil-living family. This fungus helps take crops take up nutrients
from the soil.
Aspegrillus oryzae (fungus) & Peediococus halophilus (bacteria) & Zygosaccharomyces rouxii
(fungus) & Tourulopis species (fungus) – Aspergillus gets things started by breaking down proteins
in soybeans. Zygosaccharomyces and Tourulopis break down additional proteins in beans and wheat,
giving soy sauce its distinctive flavor and rich smell.
Lactobacillus delbureckii – Turns lactose, the sugar in milk, into lactic acid that wards off microbes
that cause spoilage.
Pseudomonus putida – Cleans waste from sewage water at water treatment plants.
Lactobacillus acidophilus – Breaks down sugars and carbohydrates in milk turning it into yogurt.
This process is called fermentation.
Marine bacteria – We are using bacteria as one of the tools to clean up oil spills. These bacteria eat
the oil, turning it into carbon dioxide and other harmless by-products.
Escherichia coli – E. coli is one of many types of friendly microbes that live in your gut and help you
digest your food every day.
Microbial Record Holders
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The biggest of the big! The baddest of the bad! The oldest of the ancients! This is where you'll find all the
microbial record holders, microbes that beat all others hands down in a variety of categories. This is our
microbial Book of World Records.
Monsters Among the Microbes
The name "microbe" suggests creatures that are so tiny you need a microscope to see them. For most
microbes, this is true. But, there are some gigantic microbes that we can actually see with the unaided eye.
You’ll read about the biggest of the big in each of the main categories of microbes: bacteria, protists, fungi
and, as an extra-added bonus, parasitic worms.
Biggest Bacterium
The giant among bacteria is a single-celled “monster” that lives in the ocean and is named Thiomargarita
namibiensis (thigh-oh-mar-ger-ee-tuh nah-mih-bee-en-sis). This means, "sulfur pearl of Namibia." It was
found in the ocean floor off the coast of Namibia in Africa. T. namibiensis’s ball-shaped cells can grow to
almost 1 millimeter or 1/25th of an inch in diameter. That’s about as big as the period at the end of this
sentence. Comparing a T. namibiensis cell to an ordinary bacterium would be like comparing a 75-foot (23meter) blue whale is to a newborn mouse. Wow!
T. namibiensis "eats" sulfur and "breathes" nitrate. It stores these molecules in bubble-like compartments in
its cell called vacuoles (vac-you-ohls). These vacuoles take up 97 percent of the space inside the cell and
give the bacterium a pearly, blue-green color. These vacuoles act like food storage and scuba gear, enabling
the bacterium to survive long periods when sulfur and nitrate are scarce without "starving" or "suffocating."
A bacterium that’s big enough to be seen without the aid of a microscope is pretty amazing. But it’s a mere
dust speck when it comes to the largest protozoan…
Giants Among Protozoa
The biggest single-celled protozoa are ocean dwelling creatures called foraminifera (for-am-an-if-air-uh) or
forams for short. The largest forams can reach sizes of 5 to 6 centimeters (a little over 2 inches) in diameter.
Holy microbe, Batman! How can a single cell get that HUGE? It’s thanks in part to shells.
Forams build shells, called tests, that can support the large size these creatures reach. The tests are divided
into chambers. More chambers are added as the protozoan grows. The foram cell occupies all but the one or
two most recently added chambers
The chambers in larger foram tests often serve as a home for algae. The forams "farm" these microbes for
the food they produce as they turn sunlight into energy. Forams also eat bacteria, diatoms, other protozoa,
and small animals such as copepods. Forams are an important food source for snails, sand dollars, fish and
other creatures.
Forams move around and catch their food using hairlike extensions of their cell fluid that poke out of their
tests. These extensions are like the pseudopods (sue-doh-pods), or "false feet" that amoebas form, only
they’re much thinner and more numerous.
Ok, so 2-inch wide protozoa are definitely huge on the microbial scale, but forams don't hold a candle to the
giants among fungi…
Humongous Fungus
There’s one fungus that’s bigger than all the rest. It forms structures that spread for miles and that kills large
trees. It’s called Armillaria ostoyae (are-mill-are-ee-uh ah-stoy-ee), known more commonly as the honey
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mushroom. A fungus that can cover an area larger than 1,600 football fields definitely takes the prize for
biggest of the big.
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