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There are three main types of archaea: the crenarchaeota (kren-are-key-oh-ta), which are characterized by their ability to tolerate extremes in temperature and acidity. The euryarchaeota (you-ree-are-key-oh-ta), which include methane-producers and salt-lovers; and the korarchaeota (core-are-key-oh-ta), a catch-all group for archaeans about which very little is known. Among these three main types of archaea are some subtypes, which 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.
Then microbiologist Carl Woese devised an ingenious method of comparing genetic information showing that they could not rightly be called bacteria at all. Their genetic recipe is too different.
So different Woese decided they deserved their own special branch on the great family tree of life, a branch he dubbed the Archaea.
When is a life form not a life form? When it's a virus.
Viruses are strange things that straddle the fence between living and non-living. On the one hand, if they're floating around in the air or sitting on a doorknob, they're inert. They're about as alive as a rock. But if they come into contact with a suitable plant, animal or bacterial cell, they spring into action. They infect and take over the cell like pirates hijacking a ship.
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.
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.)
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.
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.
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.
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 is 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.
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.
(Click on image above to view animation.)
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.