Team:BYU Provo/Project/Background

Bacteriophages

Cholera

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

Since being discovered in 1915, bacteriophages have been utilized in a variety of different methods. After their discovery, phages were immediately considered for use as a treatment for bacterial infections. In the early 1920's, several institutes began developing phages commercially to treat disease. However, the discovery of antibiotics reduced the interest in using phage as a treatment as people found antibiotics more appealing. Scientists began using phages to study genetic material, clone DNA, and study the mechanism of transcription. Important discoveries, such as Hershey and Chase proving DNA is the genetic material and Jacob, Meselson, and Brenner discovering mRNA, have made phages a valuable research subject. Eventually, interest renewed in using phage as a treatment for bacterial infections. Bacteria began developing resistances towards antibiotics and scientists turned to phage once again as a potential treatment. Today, countries around the world have begun using phage as a treatment to cure disease. As people begin to recognize the many potentials of phages, it is probable that their use will become more widespread.

Emerging Use of Phage

Phage as a delivery system: One of the newest research areas, and one that we as an iGEM team have tried to tap into is the use of bacteriophages as delivery systems. Even if the phage itself isn't being used as an antimicrobial agent, its specific properties can be altered to deliver treatments to an area infected with a specific pathogenic bacteria.

Phage and Antibiotics: Antibiotics, when first discovered were something of a miracle. Bacterial infections could be cured quickly and effectively with a simple shot in the arm. But what where antibiotics have been seen to fall short, bacteriophages may be a viable solution. Antibiotic resistant strains of bacteria can be combated with use in conjunction with bacteriophage therapy.

Phage used to induce bacteria: Another emerging use of phage that our team has tried to incorporate into our research is the use of bacteriophage in bacterial induction. Bacteriophages can be used to induce genes in a bacterial cell to be turned on or off, which allows us to alter the function of the cell.

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.