Team:WPI Worcester/Design

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Design

In order to design a project to disrupt biofilm formation on field crops, the team needed to break the project down into smaller experiments. One of the most important aspects was finding out how biofilms grew on leafy crops, so we looked into how this occurs. Then, we researched current studies on the antimicrobial properties of both Antifreeze Proteins and Curcumin. Lastly, we wanted to determine a way to make plants express these antifreeze proteins using a team-built gene gun.

Biofilm Formation on Crops

Biofilms are formed by a community of bacteria, protists, or fungal cells that create a cellular matrix and cling to a surface. Biofilms are found everywhere; on teeth, your gut, metals, leafy vegetables, the surface of ponds, etc. When a biofilm is formed, the bacteria produce a sticky substance that attaches and holds the cells together and adheres them to a surface. The sticky substance is made up of proteins, sugars and nucleic acids and is called a extracellular polymeric substance. Biofilms have channels within them to allow nutrients and waste to travel to and from the cells. Biofilms can grow and and divide in order to grow in other areas. Biofilms form to increase their survival under stress;such as a lack of water, the presence of toxic substances, low or high pH, and more. Quantifying biofilms can be difficult because their contents are small and there are not many available procedures to follow. The thickness of a biofilm and the rate at which it grows is important to know. We choose to quantify biofilms by growing cultures from a number of bacterial strains, normalizing the absorbance levels to 0.1 and plating them in round bottom well plates to grow for 48 hours. We used crystal violet to dye the biofilms and compared the results from the plate reader to a standard curve made with the crystal violet dye and acidic acid.

Antifreeze Proteins' Antimicrobial Properties

Antifreeze proteins are a class of proteins produced by certain vertebrates, such as fish and insects, plants, bacteria and fungi. They allow organisms to survive in subzero environments. The proteins bind to ice crystals to prevent the growth and recrystallization of ice that would harm the organism’s ability to grow and survive. Antifreeze proteins are known to have anti-virulent properties and be able to disrupt the formation of biofilms. The proteins may bind to the biofilm in a similar way in which they bind to ice disrupting the development of the film. This project is based on multiple journal articles that look at the antimicrobial action of antifreeze proteins. However, there is not a lot of published research on the mechanism of action of these proteins against microbes. We wanted to connect this new research on antifreeze proteins’ antimicrobial action to a real world application; on crops.

Impact of Curcumin on Biofilms

Curcumin, the active ingredient of the spice turmeric, originates from the rhizome Curcuma longa. The compound possesses a yellow hue, and has been used in alternative medicine as an anti-inflammatory agent, and has recently been explored for potentially possessing an antibacterial ability. Curcumin apparently achieves its antibacterial nature from lysing the cell membranes of both Gram-positive and Gram-negative bacteria. Though the composition of bacterial types differ, this compound perforates bacterial membranes to allow the contents of each cell type to eject into the extracellular space, thereby killing the cells in the process. Specifically, by virtue of possessing an amphipathic chemistry, curcumin can selectively insert into lipid bilayers and disrupt the native structure. As biofilms develop through quorum sensing mechanisms (the communication pathways between bacteria that selectively activates gene transcription via signaling molecules), the breakdown of cellular membranes does away the entryways of such molecules. Therefore, if bacteria survive initial membrane perforation, they lose the ability to accurately secrete and absorb signaling molecules to further biofilm growth.

Creating Transgenic Plants

There are two methods we choose to experiment with to make plants express antifreeze proteins. The first approach is known as a biolistic method and it involves using a gene gun. We choose to build our own gene gun instead of purchasing one. This method has been used in past experiments in grasses, rice, wheat and corn. The DNA of interest is bound to very small particles made of gold or tungsten and shot into the plant cell. The other method we choose to investigate involves transforming the gene of interest into a tumor inducing plasmid and dipping the plants into a solution of the bacteria and collecting the seeds. This method has been used on potatoes and tomatoes in past research. This method will hopefully be used in future experiments if time permits.