The idea behind this project was to check whether defense systems that protect bacteria against phage infection can be harnessed to protect dairy bacteria against viruses that infect them. Milk and its fermentation derivatives, yogurt and cheese, are globally consumed at rates of >750 million tonnes annually, and are responsible for ~10% of the protein consumption worldwide, and in the process of yogurt and cheese production, starter cultures of lactic acid bacteria (LAB) are added to milk, leading to fermentative production of the end product. During fermentation, growth of starter culture bacteria is frequently impaired by viruses (phages) that infect these bacteria. Phage infection of lactic acid bacteria fermentative cultures is the main cause for incomplete or delayed fermentation processes in the dairy industry, and it is estimated that 10% of dairy fermentation processes fail due to culture infection by phage.
The Sorek lab discovered a number of defense systems that protect bacteria from phage infection. The idea was to test whether these defense systems can be moved, in a non-GMO sort of way, to specifically protect LABs against phages that infect them. As part of this project, we attempted to use natural transfer methods that do not rely on cloning or engineering of the receiving bacterium, and will hence result in a non-GMP organisms that can be used for food production without the fear of it being GMO. A central part of this project was to show that natural conjugative plasmids can transfer DNA from an organism that carries the defense system into an organism that does not carry it. We attempted such conjugation in many different conditions, using many different combinations of selectable markers on both the donor and the receiving organism, to try and isolate a receiving organism that has accepted the DNA payload. This turned out to be much more challenging than originally anticipated, and in fact out of the multiple pairs of organisms we experimented with, we could not see a successful transfer of the DNA payload into the bacterium.
