Engineering a whole-cell zinc biosensor

Abstract

Malnutrition is a significant healthcare concern across the globe. Though normally evocative of images of starvation or hunger, malnutrition also encompasses deficiencies of critical micronutrients such as zinc. Studies have implicated zinc malnutrition as a contributing factor to numerous developmental disorders and to diarrheal disease, one of the leading causes of death among children. However, current analytical techniques are inappropriate for measuring population-level deficiency in locations where these measurements are most needed. An effective test must be inexpensive to produce, require little training to administer and interpret, and be usable at point of care, eschewing sample transportation and expensive laboratory techniques. As obligate consumers of zinc, bacteria possess diverse cellular machinery to sense and regulate intracellular zinc concentrations in response to changes in their environment through allosteric transcriptional regulation of a variety of mechanisms of zinc influx, efflux, or sequestration. Bacteria are also relatively simple and inexpensive to produce at scale. This work describes efforts to leverage existing cellular mechanisms to sense and respond to zinc, to tie that response to heterologous pathways to produce human-readable pigmented metabolic outputs, to tune the machinery to respond to medically relevant levels in serum rather than levels originally useful to the bacterium, and to grow the resulting biosensor in human serum to demonstrate proof-of-principle of a whole cell zinc biosensor as the basis of inexpensive, colorimetric zinc assay, deployable directly at point of care with no additional analytic equipment.