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 a whole-cell bacterial biosensor harnessing these properties for use in a diagnostic test for blood micronutrient status, specifically for the detection of zinc levels in blood.  The test is 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 that are visible to the naked eye in response to zinc levels. In one implementation, we have used pigments as readouts for the biosensor.  With appropriate transcriptional control, pigment-based color changes could be essentially switch-like, reducing ambiguity in the interpretation of test results.  Moreover, production of even a small amount of pigment-producing enzyme could enable synthesis of sufficient pigment to be visible to the naked eye, potentially decreasing the total time to coloration and the biochemical burden on the cell.  In another implementation, we have used chromoproteins as indicators. Chromoproteins have different potential advantages, including that they require substantially less DNA, which simplifies cloning and other molecular biology manipulations. Here we present results from our bacteria that produce multiple visible colors in response to zinc levels, as well as the results of our efforts to tune these sensors using a variety of metabolic engineering strategies, including changes in promoters, ribosomal binding sites, and transporters.