Protista

Microbe Gallery

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Types of Microbes

Microbes can be divided into six main types: Archaea, Bacteria, Fungi, Protista, Viruses, and Microbial Mergers.

methanopyrus

Archaea

These bacteria look-alikes are living fossils that are providing clues to the earliest forms of life on Earth.
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lactobacillus sake

Bacteria

Often dismissed as “germs” that cause illness, bacteria help us do an amazing array of useful things, like make vitamins, break down some types of garbage, and maintain our atmosphere.
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lentinula edodes

Fungi

From a single-celled yeast to a 3.5-mile-wide mushroom, fungi do everything from helping to bake bread to recycling to decomposing waste.
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amoeba_proteus

Protista

Plant-like algae produce much of the oxygen we breathe; animal-like protozoa (including the famous amoeba) help maintain the balance of microbial life.
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rotavirus

Viruses

Unable to do much of anything on their own, viruses go into host cells to reproduce, often wreaking havoc and causing disease. Their ability to move genetic information from one cell to another makes them useful for cloning DNA and could provide a way to deliver gene therapy.
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niebla lichen

 

 

Microbial Mergers

Mergers and collaborations on a minute scale paved the way for higher life forms. Today, symbionts (the scientific terms for these mergers) help fertilize plants, construct coral reefs, and help us digest food.
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Lichen image courtesy of Sylvia and Stephen Sharnoff, the Center for Latin American Studies, University of California, Berkeley. Others, courtesy of MicrobeLibrary.org.

 

Protista

Algae, Protozoa, Slime Molds, and Water Molds

p_dinoani

Protists are eukaryotic creatures <you-carry-ah-tick>, meaning their DNA is enclosed in a nucleus inside the cell (unlike bacteria, which are prokaryotic <pro-carry-ah-tick> and have no nucleus to enclose their DNA. 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.

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.

A species called Arthrobotrys dactyloides sets snares made out of loops formed by its hyphae. When a nematode comes into contact with the loops, the movement triggers the fungal cells to swell with fluid, constricting the loop like a noose around the hapless nematode. Other hyphae then grow toward the trapped prey, eventually punching through its body where they begin absorbing its fluids.

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. See the news story on Phytophthora in the News section. Fungi ruin about a quarter to half of harvested fruits and vegetables annually.

Many more interesting facts about fungi can be found throughout the Microbe website, so keep clicking and reading.

You can also get a lot of details about fungi and see some cool images at The Microbial World website.

Friendly Fungi

Some fungi are quite useful to us. We've tapped 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), aka baker's yeast, to make bread rise and to brew beer. 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.

Fungi

Fungi straddle the realms of microbiology and macrobiology.

They 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.

arm_decayarm_mushrooms

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. This tangled mass is called the fungal mycelium, and ismush_illus the part of the famous honey mushroom that spreads for miles underground.

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.

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. A few fungal

species have no cell dividers: just a long, continuous cell dotted by multiple nuclei spread throughout.

nema_seq1

The zoospores have no cell wall, are uniflagellated, and may swim for 24 hours on endogenous energy reserves. On contact with a suitable surface (e.g., a nematode cuticle), the zoospore encysts by withdrawing its flagellum and surrounding itself with a thick cell wall and then adhering to the surface. The fungi Arthrobotrys oligospora can capture a nematode when it merely touches the outside of its trap.

Animation

nema_capture_labeled

Click on image above

Bacteria

skinMany of us know bacteria only as “germs,” invisible creatures that can invade our bodies and make us sick.

Few know that many bacteria not only coexist with us all the time, but help us do an amazing array of useful things like make vitamins, break down some garbage, and even maintain our atmosphere.

Bacteria consist of only a single cell, but don't let their small size and seeming simplicity fool you. They're an amazingly complex and fascinating group of creatures. Bacteria have been found that can live in temperatures above the boiling point and in cold that would freeze your blood. They "eat" everything from sugar and starch to sunlight, sulfur and iron. There's even a species of bacteria—Deinococcus radiodurans—that can withstand blasts of radiation 1,000 times greater than would kill a human being.

contactdental

Classification

leucothrix

Bacteria fall into a category of life called the Prokaryotes (pro-carry-oats). Prokaryotes' genetic material, or DNA, is not enclosed in a cellular compartment called the nucleus.

Bacteria and archaea are the only prokaryotes. All other life forms are Eukaryotes (you-carry-oats), creatures whose cells have nuclei.

(Note: viruses are not considered true cells, so they don't fit into either of these categories.)

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. And, for those of us who like to ponder more philosophical questions like the origins of the Earth, there may be some clues there as well.

How Long They’ve Been Around

cyano

Like dinosaurs, bacteria left behind fossils. The big difference is that it takes a microscope to see them. And they are older.

Bacteria and their microbial cousins the archaea were the earliest forms of life on Earth. And may have played a role in shaping our planet into one that could support the larger life forms we know today by developing photosynthesis.

Cyanobacteria fossils date back more than 3 billion years. These photosynthetic bacteria paved the way for today's algae and plants. Cyanobacteria grow in the water, where they produce much of the oxygen that we breathe. Once considered a form of algae, they are also known as blue-green algae.

Bacteria are among the earliest forms of life that appeared on Earth billions of years ago. Scientists think that they helped shape and change the young planet's environment, eventually creating atmospheric oxygen that enabled other, more complex life forms to develop. Many believe that more complex cells developed as once free-living bacteria took up residence in other cells, eventually becoming the organelles in modern complex cells. The mitochondria (mite-oh-con-dree-uh) that make energy for your body cells is one example of such an organelle.

Life at the Extreme

Many archaeans thrive in conditions that would kill other creatures: boiling water, super-salty pools, sulfur-spewing volcanic vents, acidic water and deep in Antarctic ice. These types of archaea are often labeled "extremophiles," meaning creatures that love extreme conditions.

pyrodictium

Archaeans have been found that can live in temperatures above 212°F (100°C). In contrast, no known eukaryotes can survive over 140°F (60°C). Other archaeans have been found in an Antarctic lake with a surface that is permanently frozen.

How do these extremophiles do it? They make a variety of protective molecules and enzymes (en-zimes). For example, some archaeans live in highly acidic environments. If the acid got into the archaeal cells, it would destroy their DNA, so they have to keep it out. But the defensive molecules on their cellular surfaces do come into contact with the acid and are uniquely designed not to break apart in it. Archaeans that live in very salty water are able to keep all the fluid from dissolving out of their cells by producing or pulling in from the outside solutes such as potassium chloride that balance the inside of the cells with the salty water outside. Other enzymes allow other achaeans to tolerate extreme hot or cold.

Not all the archaea are extremophiles. Many live in more ordinary temperatures and conditions. For example, scientists can find archaeans alongside bacteria and algae floating about in the open ocean. Some archaeans even live in your guts.

 

The Extremists

ice

gsaltlake

vent

lonestar

 

 

 

 

sulfur

Archaea can be found in many"extreme environments": highly sulfurous lakes (right); ice (top left); Utah‘s Great Salt Lake (above middle); and hot geysers like the Lonestar (above middle); and in undersea hydrothermal vents (above right).

In addition to superheated waters, archaea have been found in acid-laden streams around old mines, in frigid Antarctic ice and in the super-salty waters of the Dead Sea. A number of other extreme-living bacterial species also enjoy these conditions, too, such as the community of cyanobacteria and bacteria shown above.

 

  • Thermophiles like unusually hot temperatures. A few species have been found to survive even above 110 degrees Celsius (water boils at 100 degrees Celsius).

  • Psychrophiles like extremely cold temperatures (even down to -10 degrees Celsius).

  • Halophiles thrive in unusually salty habitats. Some can thrive in water that’s 9% salt; sea water contains only 0.9% salt.
  • Acidophiles prefer acidic conditions; Alkaliphiles prefer very alkaline environs.

Archaea that populate extreme environments (along with some of their bacterial cousins) have developed some clever tricks and tools to do so. For example, they produce special enzymes that help keep all the parts of their cells intact even in conditions that would have our human skin falling apart.

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