Microbiology

Bacterial Conjugation and Genetics



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This article will address the types of broad spectrum genetic mutation and how bacteria absorb and utilize foreign DNA.
In order to fully understand a topic an individual must first understand its meaning. Therefore I will begin with the basic definition of mutation. Tortora, Funke, and Case state that mutation is a base change in the DNA sequencing of an organism. However mutation in itself can be broken down into subcategories. For example a Silent Mutation is a change in the DNA sequence that does not interfere with the production of the amino acids that were encoded. This means that when the genetic code is translated the resulting amino acids may still produce the same proteins, or if the amino acid is altered the resultin protein will be very similar to the protein that was originally produced.

One of the most common causes of mutation is called Base Substitution. In this case the base pairs of AT and GC are switched in the genetic code, resulting in a whole new codon when translated into messenger RNA. This mutation causes the transcribed mRNA to produce completely different amino acids. These altered amino acids cause a completely new protein to be produced instead of the protein that was needed. When a base substitution has this end result it is known as a Missense Mutation.

Finally there is a Frame Shift Mutation. This is caused by the insertion or deletion of the nucleotide pairs within the genetic code. The result of this mutation is usually fatal due to the fact that it drastically alters every codon in the genetic code, causing a severe abnormality in amino acid production. These types of mutations usually occur in the presence of mutagens.

The mutations that I have previously mentioned may apply to any living organism. However Microorganisms can alter their genetic code in other ways as well. The bacteriodes for example have the ability to pass genetic traits directly to one another. This method of genetic transfer is known as bacterial conjugation. There are 2 ways that conjugation may occure. The first method is through the transmission of a cell's plasmid (genetic information) through direct cell to cell contact. The second method of conjugation occurs between Gram (+) and Gram (-) bacteria. Gram - bacteria possess a sex pili which penetrates the cell wall of a Gram + bacteria, then the Gram - bacteria sucks the Gram+ bacteria's plasmid out. Once inside the Gram - bacteria the 2 plasmids comnbine to create an altered genetic code which will of course be passed on to any bacteria produced from or mated to that bacteria.

Another method of bacterial DNA transfer is called transduction. In this case DNA is transferred between bacteria via a bacteriophage (bacteria virus). This type of DNA transfer happens in four steps. First the bacteriophage attaches to a bacteria and injects its own DNA. Second while the virus reproduces itself inside of the host cell it absorbs some of the bacteria's DNA. Third the new bacteriophages kill and leave the bacteria. Finally a bacteriophage that has absorbed only the previous host's DNA unwittingly injects bacterial DNA into the new host. This does not kill the new host but instead it alters it's DNA resulting in new bacterial traits such as air tolerance or motility.

The microbial world is a fast paced ever changing environment full of unpredictable mutations and undiscovered specimens. Luckily for us most bacteria are more helpful than harmful. We would truly be lost without them.

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