Bacteria have demonstrated an adept ability to mutate and foil drugs at a pace which nearly bests our research and development efforts. Bacteria in the human GI tract have been shown to produce vitamins and may otherwise contribute to nutrition and digestion. But their most important effects are in their ability to protect their host from establishment and infection by alien microbes and their ability to stimulate the development and the activity of the immunological tissues.

Bacteria were the sole occupants of our planet for more than half of the entire history of life; yet these single-celled organisms are among the smallest living things. These diverse creatures are abundant in all marine habitats, from the sea surface to the greatest depths.

Bacteria have been found that can live in temperatures above the boiling point and in freezing temperatures. They "eat" everything from sugar and starch to sunlight, sulfur and iron .

Bacteria and Archaea are superficially similar; for example, they do not have intracellular organelles, and they have circular DNA. However, they are fundamentally distinct, and their separation is based on the genetic evidence for their ancient and separate evolutionary lineages, as well as fundamental differences in their chemistry and physiology.

Bacteria are single-cell organisms. They are neither animals, plants nor fungi but belong in a group all of their own. Bacteria can be one of three main shapes: round, rod shaped, and spiral.

Make sure students understand that even though some bacteria can cause serious problems, most perform important functions and are necessary to maintain the health of plants, animals, and the environment. Bacteria are among the oldest living organisms on Earth, and are very small. Because the bacteria structure is so minute, it can only be seen through a microscope.

Bacteria suffer from negative public relations. You probably associate bacteria with the three Ds: dirt, disease and death. Bacteria live almost everywhere on Earth, including the soil, water, organic matter, and the bodies of multicellular animals (eukaryotes).

Some bacteria benefit humans and other plants and animals. Bacteria that lose the dye complex can be counterstained with the red dye saffranin so that they appear red. The basis of the Gram reaction lies within the structure of the cell wall, described below.

Bacteria may have one, a few, or many flagella in different positions on the cell. Bacteria are small single cells whose whole purpose in life is to replicate.

Bacteria decompose many types of organic substances and are currently being investigated as a means of decomposing unwanted synthetic chemicals ( e.g pesticides, dyes, and petroleum) that are released into the environment. A variety of commercial products can be produced by bacteria: lactic acid, acetic acid, citric acid, butanol, acetone, ethanol, and glycerol.

Bacteria are all around us. Given good growing conditions, a bacterium grows slightly in size or length, a new cell wall grows through the center forming two daughter cells, each with the same genetic material as the parent cell.