• Interdisciplinary Bio Central
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• v.3 no.3
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• pp.10.1-10.8
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• 2011

Introduction: Hash functions are computer algorithms that protect information and secure transactions. In response to the NIST's "International Call for Hash Function", we developed a biological hash function using the computing capabilities of bacteria. We designed a DNA-based XOR logic gate that allows bacterial colonies arranged in a series on an agar plate to perform hash function calculations. Results and Discussion: In order to provide each colony with adequate time to process inputs and perform XOR logic, we designed and successfully demonstrated a system for time-delayed bacterial growth. Our system is based on the diffusion of ${\ss}$-lactamase, resulting in destruction of ampicillin. Our DNA-based XOR logic gate design is based on the op-position of two promoters. Our results showed that $P_{lux}$ and $P_{OmpC}$ functioned as expected individually, but $P_{lux}$ did not behave as expected in the XOR construct. Our data showed that, contrary to literature reports, the $P_{lux}$ promoter is bidirectional. In the absence of the 3OC6 inducer, the LuxR activator can bind to the $P_{lux}$ promoter and induce backwards transcription. Conclusion and Prospects: Our system of time delayed bacterial growth allows for the successive processing of a bacterial hash function, and is expected to have utility in other synthetic biology applications. While testing our DNA-based XOR logic gate, we uncovered a novel function of $P_{lux}$. In the absence of autoinducer 3OC6, LuxR binds to $P_{lux}$ and activates backwards transcription. This result advances basic research and has important implications for the widespread use of the $P_{lux}$ promoter.