Diversity in Bacteria

Rapidly growing bacteria that are exposed to continually changing environments must be able to adapt quickly if they are going to successfully compete with other organisms in the same environment. Unless they respond quickly to take advantage ofthe change, other organisms will crowd them out. Bacteria are haploid in that they contain only a single set of genes, so any changes in a single or many genes quickly change the bacteria. Further, all offspring of the bacteria in which the change occurs also are changed.

Bacteria can adapt to a changing environment by three different mechanisms, two of which involve changes in the genetic make up of bacteria. These changes can occur by two independent means. First, the nucleotides of DNA can undergo changes in their chemical structure resulting in changes in DNA which results in organisms with different properties. These alterations are called mutations and the changed organisms are mutants. Second, bacteria can acquire genes from other bacteria through a process of gene transfer, which provides new genetic information to the cells. These changes in DNA, which are passed on to all progeny, are the basis for natural selection. If the change in genetic information allows the organism to multiply more rapidly than the original bacteria in an altered environment, then the original bacteria will be replaced in the environment. The properties of a cell determined by its DNA composition are its genotype, and if DNA is altered the genotype changes.

In addition to the changes in DNA that can occur, the expression of the genetic information encoded by the DNA can be regulated. Depending on the environmental conditions, some genes are turned on and others are turned off. The cell will tend to synthesize the proteins that it needs to multiply most rapidly. By doing this, it conserves energy and nutrients. The characteristics displayed by an organism in any given environment make up its phenotype.

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