Microorganisms-A Classification and Charecteristics

Microorganisms can be broadly classified into 6 types-Bacteria, Viruses, Fungi, Archaea, Protista, and Microbial Merges

Bacteria-

Often bacteria are shunned as invisible 'germs' that cause diseases.But you will be suprised to know that they not only coexist with us but also protec us from various diseases.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. . They are also known as 'prokaryotes'- meaning the don't have a membrane bound neucleus and their Deoxyrybo Neuclic Acids(DNA) floats in the cytoplasm.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.

But the quetion that arises in most of people's mind is that since when have they existed?

Well, Bacteria along with their cousins Archaea were the first organisms to appear on earth and they have existed pretty much since the begining of the earth. And how do we know this? Like dinosaurs, they left behind fossils- the only difference-they are microscopic.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.

Viruses-

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.

Viruses are found on or in just about every material and environment on Earth from soil to water to air. They're basically found anywhere there are cells to infect. Viruses have evolved to infect every form of life, from animal to plant and from fungi to bacteria.

However, viruses tend to be somewhat picky about what type of cells they infect. Plant viruses are not equipped to infect animal cells, for example, though a certain plant virus could infect a number of related plants. Sometimes, a virus may infect one creature and do no harm, but cause havoc when it gets into a different but closely enough related creature.

Viruses are the simplest and tiniest of microbes; they can be as much as 10,000 times smaller than bacteria. Viruses consist of a small collection of genetic material (DNA or RNA) encased in a protective protein coat called a capsid. (Retroviruses are among the infectious particles that use RNA as their hereditary material. Probably the most famous retrovirus is human immunodeficiency virus, the cause of AIDS.) In some viruses, the capsid is covered by a viral envelope made of proteins, lipids and carbohydrates. The envelopes may be studded by spikes made of carbohydrates and proteins that help the virus particles attach to host cells. Outside of a host, viruses are inert, just mere microbial particles drifting aimlessly.

A virus is basically a tiny bundle of genetic material—either DNA or RNA—carried in a shell called the viral coat, or capsid, which is made up of bits of protein called capsomeres. Some viruses have an additional layer around this coat called an envelope. That's basically all there is to viruses.

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.

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.

Archaea-
 

There are three main types of archaea: the crenarchaeota (kren-are-key-oh-ta), which are characterized by their ability to tolerate extremes in conditions 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.

 Archaea look and act a lot like bacteria. So much so that until the late 1970s, scientists assumed they were a kind of “weird” bacteria.

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.

  

Protista-

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.

Microbial Merges

Collaborations on a Minute Scale

Over millions of years of evolution, we humans have worked out a mutually beneficial partnership with the microbes that came to inhabit our guts. In return for their aid in digestion, we give them a stable, protected home and plenty of nutrients via the food we eat. We need them as much as they need us.

Microbes break down food molecules our body’s enzymes and acids can’t dissolve, helping us squeeze all the nutrients out of our food. Some make valuable vitamins that our body needs.

Many microbial species have proved to be consummate evolutionary wheelers and dealers, arranging collaborations, mergers, and acquisitions that usually serve both partners well.

MERGERS OF NOTE

Rhizobia are bacteria that form nodules on the roots of legumes to supply them with nitrogen; in return, the plants provide the bacteria with carbohydrates.

Mycorrhizae are soil-dwelling fungi that act as extensions of plants’ roots, enabling them to vastly increase their nutrient-absorbing network. The plants provide the fungi energy in the form of carbohydrates.

Zooxanthelle are photosynthetic algae that live inside the body tissues of coral polyps. They provide nutrients to their polyp hosts in exchange for a protected, stable environment and nutrients they need for growth.

Lichens are an alliance of fungi and algae that allows each to grow in environments where neither could survive alone, like deserts, rocks, or tree bark.