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An Externally-Tunable Bacterial Band-Pass Filter for Enzymatic Activity

Takayuki Sohka1, Richard A. Heins1, Ryan M. Phelan2, Jennifer Greisler1, Craig A. Townsend2, and Marc Ostermeier1. (1) Chemical and Biomolecular Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, (2) Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218

Synthetic biology aims at the assembly of complex biological systems using a network of robust, tunable, biological building blocks. The current paradigm for tuning synthetic biological systems is through reengineering system components. However, such an approach is tantamount to building a new device for each desired network behavior. Biological systems designed with the inherent ability to be tuned based on external stimuli will be more versatile. We engineered E. coli cells to behave as a band-pass filter for enzyme activity and small molecules. The band's location and band-width can be positioned within a four order of magnitude range simply by the addition of compounds to the growth media. Inclusion of an enzyme-substrate pair that functions as an attenuator in the network enabled this tunability. The system enabled bacteria growth to be patterned in response to chemical gradients in non-intuitive ways linear patterns could be induced from radial concentration gradients. Mixtures of cells with different levels of enzyme activity could be induced to grow in a differentiated pattern corresponding to a rank order of enzyme activity. The system was used to isolate an engineered allosteric enzyme from a library of inactive and non-allosteric enzymes. The application of this strategy to other synthetic biological systems will increase their utility for biotechnological applications and their usefulness as a tool for gaining insight into biological network behavior and nature's underlying design principles.