Bacterial GeneticsBacterial Genetics

A very, very, very brief A very, very, very brief introduction………introduction………

Introduction:Introduction:

Bacteria have four important Bacteria have four important advantages for "traditional types of advantages for "traditional types of genetic experiments":genetic experiments": They are haploid (no masking). They are haploid (no masking). New generation is produced every 20 New generation is produced every 20

minutes. minutes. Easy to grow in ENORMOUS Easy to grow in ENORMOUS

NUMBERS. NUMBERS. Individual members of these large Individual members of these large

populations are GENETICALLY populations are GENETICALLY IDENTICAL (or very nearly so).IDENTICAL (or very nearly so).

Bacteria is easy to grow:Bacteria is easy to grow:

3 3 MAJOR TYPESMAJOR TYPES of genetic of genetic transfer found in bacteria:transfer found in bacteria:

Transformation - this is what Avery Transformation - this is what Avery characterised remember? Somehow characterised remember? Somehow or another, the bacteria can take up or another, the bacteria can take up externally provided DNA.externally provided DNA.

Conjugation - DNA is transferred Conjugation - DNA is transferred from one bacteria cell to another, via from one bacteria cell to another, via "sex pilli". "sex pilli".

Transduction - this is where DNA is Transduction - this is where DNA is introduced into bacteria by injection introduced into bacteria by injection from a bacteriophage. from a bacteriophage.

Bacterial TransformationBacterial Transformation

"Transformation" is simply the "Transformation" is simply the process where bacteria manage to process where bacteria manage to "uptake" or bring in a piece of "uptake" or bring in a piece of external DNA (somehow or external DNA (somehow or another). Usually, this process is another). Usually, this process is used in the laboratory to introduce a used in the laboratory to introduce a small piece of PLASMID DNA into a small piece of PLASMID DNA into a bacterial cell. bacterial cell.

DNA is the genetic material - DNA is the genetic material - The First demonstration of The First demonstration of bacterial transformationbacterial transformation. . Experiments done by Experiments done by Frederick Griffith (in London) Frederick Griffith (in London) in 1928 found there were two in 1928 found there were two different types of the different types of the bacterium bacterium Streptococcus Streptococcus pneumoniae:pneumoniae:

An "S" or SMOOTH coat strain, which is lethal to the mice.

                                                                                          

   

An "R" or rough strain, which will not hurt the mouse.

                                                 

Griffith found that he could heat inactivate the smooth strain.

                                                              

However, if he were to take a mixture of the heat-inactivated S strain, mixed with the R strain, the bacteria would die.  Thus there was some Material in the heat-killed S strain that was responsible for "transforming" the R strain into a lethal form.   

                                                                                                     

Griffith (and a lab co-worker) was Griffith (and a lab co-worker) was killed in their laboratory in 1940 killed in their laboratory in 1940 from a German bomb. However, from a German bomb. However, their work continued on in the U.S., their work continued on in the U.S., and in 1944, Oswald Avery, C.M. and in 1944, Oswald Avery, C.M. MacLeod, and M. McCarty carefully MacLeod, and M. McCarty carefully demonstrated that the ONLY demonstrated that the ONLY material that was responsible for material that was responsible for the transformation was DNA - thus, the transformation was DNA - thus, DNA was the "Genetic material" - DNA was the "Genetic material" - however, many scientists were still however, many scientists were still not sure that it was REALLY DNA not sure that it was REALLY DNA (and not proteins) that was the (and not proteins) that was the genetic material. responsible for genetic material. responsible for "transforming" the R strain into a "transforming" the R strain into a lethal form. lethal form.

McCarty,M., McCarty,M., The Transforming The Transforming Principle - Discovering that Principle - Discovering that Genes are made of DNA, Genes are made of DNA, (New (New York: W.W.Norton & company, York: W.W.Norton & company, 1985) - Although this book was 1985) - Although this book was written about 40 years after the written about 40 years after the experiments took place (1985), experiments took place (1985), it is an excellent history of the it is an excellent history of the research that was going on in research that was going on in the early 1940's the early 1940's

The genetic transfer of streptomycin resistance (strr) to the streptomycin sensitive (strs) cells of E.coli. The recovery of strs cells depends on the concentration of the strr DNA.

Co-transformation is simply the Co-transformation is simply the simultaneous transformation of two simultaneous transformation of two different DNA fragments. different DNA fragments.

First, you must obtain your DNA - you First, you must obtain your DNA - you can do this by isolating DNA from a nice can do this by isolating DNA from a nice bacteria that has some DNA you want to bacteria that has some DNA you want to

use....use....

  

                                              

First, you must obtain you DNA - you can do this by isolating DNA from a nice bacteria that has some DNA you want to use.... 

Now you do the transformation and have a look at the products - if you're transforming into a strain that lacks the gene of interest (which you usually are), then the process is quite easy - just look for colonies that carries the trait of interest:

Bacterial ConjugationBacterial Conjugation

Bacterial conjugation is the Bacterial conjugation is the pocess in which DNA is pocess in which DNA is transferred from a bacterial transferred from a bacterial donor cell to a recipient cell by donor cell to a recipient cell by cell-to-cell contact. It has been cell-to-cell contact. It has been observed in many bacterial observed in many bacterial species and is best understood species and is best understood in E.coli, in which it was in E.coli, in which it was discovered by Joshua discovered by Joshua Lederberg in 1951.Lederberg in 1951.

"SEX in a Blender"By some clever use of timing experiments, it is possible to generate a genetic map of E.coli!                                    

Chromosome Mapping:Chromosome Mapping:

Transduction:Transduction: