A new type of biosensor
In the western world, we take safe drinking water for granted. But in many parts of the world, clean water is a luxury that is not always available. It takes an enormous amount of effort to ensure that our water is safe for use and free of contamination. New technologies have the potential to make it easier and cheaper to test water, and make clean water more broadly available. To aid in that effort, we aimed to develop a method which detects water contamination by designing a new type of biosensor. To do that, we made use of the plant immune system.
Pattern recognition receptors
Plants are masters of pathogen detection. Since they can’t run from threats like animals can, they have developed sophisticated receptors and associated systems to detect bacteria, viruses and fungi. One especially interesting family of receptors are “pattern recognition receptors” or PRRs. PRRs mediate the first layer of the plant’s defence by detecting a variety of distinct, evolutionarily highly conserved epitopes that are essential for survival of the pathogen. These epitopes are commonly referred to as microbe- or pathogen-associated molecular patterns (MAMPs/PAMPs).
We want to develop a biosensor that makes use of the qualities of PRRs to detect bacterial contamination in water. For that, we express PRRs in our detector organism, Saccharomyces cerevisiae. To detect as many bacteria as possible, we selected a number of PRRs that sense epitopes which are ubiquitous and highly conserved across a wide range of bacteria. The EFR receptor detects the bacterial molecule “EF-Tu”, FLS2 detects flagellin, and CORE detects the cold-shock protein.
To make pathogen detection measurable, we chose a simple, luminescence based output. Our chosen PPRs dimerize with their co-receptor BAK1 when they bind to their epitope. We make use of that dimerization by fusing one half of a split luciferase to the receptor and co-receptor. Upon ligand binding, the two halves are brought together and the luciferase is restored, producing a quantifiable luminescent output. This approach allows initial testing of water samples delivering a rapid visual output to measure microbial load.