Working with Sachiko

The arsenic sensing bacteria was made by Dr. Jan Roelof van der Meer. The arsenic reporter is built on a naturally occurring bacterium which is resistant to arsenite and arsenate. The E.coli is genetically modified with Green Fluorescence Protein (GFP) acquired from jellyfish to emit fluorescence.A repressor protein is attached to specific points on the DNA of the bacteria. This prevents a reaction from taking place within the DNA thus stopping it from emitting fluorescence. When the bacteria come in contact with the contaminated water, the arsenic penetrates the cell wall. At this stage the repressor protein, which has an affinity for arsenic, releases itself from the DNA and binds to the arsenic. Thus a reaction takes place through the DNA which results in fluorescence exposed to UV light.

The Lysogenic Broth(LB) serves as a potential food source for the bacteria. Once the equipment is autoclaved, two cultures were made – one liquid and another on agar plates.The LB solution was prepared by mixing the LB powder with distilled water. Kanamycin, an antibiotic, was added to the LB to kill any other strains of bacteria that may have been present. The strain of bacteria was genetically modified to resistance kanamycin. Agar was added to one half of the solution and set in petri dishes over-night. The preserved genetically modified bacteria were added to the other half. Different dilutions were made by adding water in various proportions. They were then left in an orbital shaker overnight to allow the growth of the bacteria. The dilutions were then spread over the agar plates that had set over night. They were sealed and the bacteria were left to cultivate. Later, the plates were stained. Favorable colonies were chosen and were used to test water for arsenic poisoning. A new glycerol stock was created with the selected bacterial colony and preserved for future use.