Growth. Reproduction and genetic transfer

Bacterial growth usually refers to an increase in the number of bacteria, rather then to an increase in its size. A colony is a large group of bacteria, such as that grown on a nutrient plate in a laboratory. All the members of colony are descendants of a single bacterium. All bacteria need food and water and many need oxygen. Other factors that influence growth are temperature, sunlight and chemicals.

Under ideal conditions, some bacteria can reproduce every 20 to 30 minutes. Bacteria usually reproduce through binary fissions, or splitting in two. Each new cell is exactly like the parent cell. Mutations, the result of errors or changes in the genetic code, account in part for the extraordinary ability of bacteria to adjust to differing conditions (Tabl. 3.1).

Genetic material in some cases is transferred from one bacterium to another, resulting ingenetic recombination. When the bacterium later divides, it passes on its new genes to the daughter cell. In this way, resistance to antibiotics can be transferred from one of bacteria to another.

In a process called conjugation, a donor bacterium transfers genetic material to an acceptor bacterium through direct contact.

Transformation process transfers genetic material from a dead strain, or genetic type, of bacteria to a live strain.


Main groupes of bacteria


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.

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