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- Bacteriophages
- Cholera
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Bacteriophages
Phage as an Organism
Bacteriophages are viruses that infect bacteria. They are composed of a capsid and a tail made of protein. Inside the capsid, bacteriophages have either a DNA or RNA genome. Because they are so simple, they cannot replicate on their own. To do so, a bacteriophage must attach to a bacterial cell membrane and inject its genome into the cell. The bacterial cell's machinery will replicate the genome and produce the viral proteins. These come together to make new bacteriophage progeny that will subsequently exit the cell.
Traditional Use of Phage
Emerging Use of Phage
Cholera
Cholera, the Disease
Cholera is a disease that affects three to five million people each year with approximately 100,000 deaths. Transmitted mainly by the drinking-water supply, it causes an infection in the small intestine leading to severe diarrhea and vomiting. If left untreated, it can cause death within hours. The disease is caused by the bacterium Vibrio cholerae which was first isolated by Filippo Pacini in 1854. Vibrio cholerae is gram negative, comma shaped, and flagellated. It is easily treated with modern water purification techniques, and as such it is most prevalent in developing countries that lack this infrastructure. Countries that are recovering from natural disasters are especially vulnerable. One of the first documented outbreaks occurred in 1817 near the Ganges River. British trade ships unknowingly spread the disease by transporting infected bilgewater from the Bay of Bengal. Several major outbreaks followed in places including as London, New York, and several parts of Russia.
Quorum Sensing
Quorum sensing is the cell-to-cell signaling system that allows for coordinated behavior between bacteria through the secretion and detection of signaling molecules termed autoinducers. Some autoinducers are specific to a certain bacteria, while others are detectable by a broad range of bacteria. The N-acyl-L-homoserine lactones (AHLs) are a class of autoinducer secreted by many Gram-negative bacteria, including Vibrio cholerae. While Escherichia coli does not produce AHLs, it does have the SdiA receptor necessary to detect these autoinducers. The binding of AHLs from V. cholerae to the SdiA receptor on E. coli triggers a signal cascade that activates the transcription of quorum sensing linked genes in E. coli. By inserting our target genes into the quorum sensing linked section of E. coli’s DNA, we can design a specific response to the detection of V. cholerae by E. coli.
Biofilm
Bacteria living in a biofilm are physiologically different from a bacterium of the same species in a planktonic state. In a biofilm, cells are fixed within a self-produced extracellular polymeric substance (EPS.) Vibrio cholerae's virulency is one of the physiological changes it undergoes when changing its physical sate. The formation of its biofilm is reciprocally controlled by two chemical signaling systems: 3’,5’-cyclic diguanylic acid (c-di-GMP,) which activates biofilm formation, and quorum sensing, which represses it. Many species of bacteria in the Vibrio genus form biofilms, although they are very different in their structure and stability. Vibrio cholerae produces a biofilm that is free floating rather than one that attaches to solid surfaces which presents major issues in characterizing and running degradation assays on it.
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