The bacterium Borrelia burgdorferi is responsible for Lyme disease.

They are frequently portrayed as harbingers of disease and death. The news is always reporting about some bacteria or virus such as the human immunodeficiency virus (HIV), cholera, the West Nile virus, or E. coli causing illnesses around the world. Throughout modern and ancient times alike, these unseen organisms have caused the deaths of millions of people.

A drawing of a simple bacterium's cellular structure

But most bacteria are harmless, and without them, life on Earth could not exist. They are essential components of the global ecosystem as decomposers.

Viruses, on the other hand, are mostly harmful. They exist only to invade cells and reproduce themselves, usually destroying the host cell in the process.

BACTERIA are a group of simple, microscopic, single-celled organisms. A bacterium's cell is very different from a plant or animal cell.It has no organelles such as a nucleus or mitochondria inside its cell wall.

Viruses are a bit more complicated than bacteria. A VIRUS is only a strand of DNA or RNA covered by a protein shell. Viruses are not considered cells. Some scientists are not even sure if these "life forms" are alive.

If bacteria are so important to the ecosystem, and if viruses are so deadly, where are they? Everywhere!

In order to see bacteria and viruses, we must magnify them thousands of times.

Both bacteria and viruses are very small. Bacteria can be seen only with the help of a microscope that magnifies them one thousand times. To see viruses, scientists need to use an electron microscope that magnifies them one million times their normal size.

The world teems with bacteria and viruses. They are in the soil, in streams, in oceans, and in and on animals and plants. They can live in a wide variety of environments ranging from the bottom of the ocean to the top of the highest mountain. These microscopic organisms live their lives without much notice by humans (unless they cause disease).

Who Needs Bacteria?

© Missouri Conservation Commission

Decomposers include bacteria, fungi, worms, and insects.

Bacteria are very adaptable life forms. Scientists theorize that bacteria are the earliest known organisms, and it is possible that all life on Earth evolved from these simple yet hardy life forms. But it's always the bad things about bacteria that people remember. They cause illnesses such as strep throat, ear infections, and food poisoning (salmonella and botulism for example).

An Unwelcome Guest

The AIDS virus attaches to a receptor on one of the immune system's helper T cells.

At first, viruses were thought to be the simplest forms of life. But they are not cells and can do nothing outside a host cell. Viruses cause diseases such as chicken pox, head colds, the flu, and AIDS.

So What?

This innocent-looking virus causes the often-deadly Ebola hemorrhagic fever.

Finally, we will try to answer the question, Are viruses alive? This question might seem simple to answer at first glance because viruses are discussed as living things: "Flu viruses are annoying," "She has a nasty cold," or "Ebola viruses are deadly." But just because viruses seem alive, does it mean they really are?

As we uncover the amazing world of the bacterium and the virus, we will also discuss antibiotics and vaccines. Bacteria and viruses are important to Earth's ecosystems and play an integral role in the human experience.