Pigment-Based, Low-Cost, Portable Micronutrient Status Tests Using Engineered Bacteria

Micronutrient deficiencies are a significant healthcare concern across the globe. Significant even in some developed nations, micronutrient deficiencies are more severe in the developing world and locally in the wake of major disasters. These conditions, though easily treated, remain a problem because they are often difficult to recognize and diagnose, requiring lab tests that are prohibitively expensive in both material and human resources for those in developing or remote areas.

As obligate consumers of the same micronutrients, bacteria possess cellular machinery to control intracellular micronutrient levels and have corresponding regulatory mechanisms to respond to varying concentrations in their environment. We have developed whole-cell bacterial biosensors harnessing these properties of bacteria for use in a diagnostic test for blood micronutrient status.  The tests are designed to be inexpensive in total cost of operation, requiring no complex equipment and minimal medical training to administer and interpret. This would obviate the logistical problem of laboratory access and sample transport in remote and low-resource environments, allowing on-site diagnosis of micronutrient deficiencies in the populations most at risk.

To create this biosensor, we designed and implemented genetic circuitry to trigger specific changes in color in response to defined micronutrient levels. In particular, we use pigments as readouts for the biosensor, not only for their naked eye visibility but because with appropriate metabolic engineering, color changes could be essentially switch-like, reducing ambiguity in the interpretation of test results.  Moreover, production of even a small amount of protein could enable synthesis of sufficient pigment to be visible to the naked eye, potentially decreasing deleterious effects on the cell.  Here we present the results of our efforts to create and tune this sensor using a variety of metabolic engineering strategies, including changes in promoters, ribosomal binding sites, and transporters.