3.2.2. Main groupes of bacteria Archaebacteria

The final numbers were punched into the computer. After a slight delay, the results flashed onto the screen. But the result was unexpected and astonishing.

The computer had just completed the final steps of an important study. To begin the study, scientists had taken RNA, a chemical similar to DNA, form more than 200 different kinds of organisms. The RNA was broken apart and examined. Each slight difference in the RNA of the 200 organisms was analyzed. The computer grouped the organisms by the similarity of their RNA. An amazing pattern emerged. Scientists expected two kinds of cells: simple and complex. But there were three. The simple cells were not all alike. The unexpected cells were tiny organisms that looked like bacteria, but inside, they were quite different.

These organisms might make up a new kingdom. They have some of the characteristics of complex cells. They also differ from most true bacteria in several ways. For example, they are poisoned by oxygen. They need only simple molecules to survive. Their cell walls are chemically different from the cell walls of other bacteria. And, finally, they live in harsh or strange places. Some live in the digestive tracts of animals. Others live in hot springs, deep oceans, marshes or very salty places such as the Great Salt Lake.

Some scientists think these bacteria are just the type of organisms that might have survived the harsh conditions on earth. For this reason, they suggest naming the organisms Archaebacteria which means "first bacteria".

Scientists are excited about newly discovered type of simple cell. The Archaebacteria will be important to scientists who try to understand how living things are related to one another.

Photosynthetic bacteria

Among the eubacteria are three photosynthetic forms: the green sulphur bacteria, the purple sulphur bacteria and the purple nonsulphur bacteria. (The colors of third group may actually range from purple to red or brown). Like the green plants, photosynthetic bacteria contain chlorophyll molecules composed of a magnesium-containing porphyry ring and a lipid tail. The chlorophyll found in the green sulphur bacteria is chemically very similar to the chlorophyll a of higher plants. The chlorophyll found in the two groups of purple bacteria is bacteriochlorophyll, which differs chemically in several details from chlorophyll a and is a pale blue-gray. The colors of the purple bacteria are to the presence of several different yellow and red carotenoids, which function as accessory pigments in photosynthesis.

In the photosynthetic sulphur bacteria, the sulphur compounds are the electron donors playing the same role in bacterial photosynthesis that water does in plant photosynthesis.

General equation of the photosynthesis:

All bacterial photosynthesis is carried out anaerobically, and it never results in the production of molecular (O₂).

In the nonsulphur photosynthetic bacteria, other compounds, including alcohols, fatty acids, and a variety of other organic substances, serve as electron donors for the photosynthetic reaction