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Color Theory

A bacterium engineered to produce different pigments in response to varying micronutrient levels in blood samples could give health officials an inexpensive way to detect nutritional deficiencies affecting human populations in resource-limited areas of the world. This “bacterial litmus test,” which currently measures levels of zinc, would make results visible as simple color changes — without using any sophisticated equipment.

More than a billion people worldwide may be at risk for inadequate zinc intake, but measuring zinc levels currently requires sophisticated testing equipment not available in many affected areas. If field tests show the biosensor can successfully measure zinc levels, the researchers hope to extend the concept to other micronutrients, including vitamins.

“We think this is just enough technology to meet the needs,” said Mark Styczynski, an assistant professor in the Georgia Tech School of Chemical & Biomolecular Engineering. “The information we can provide could one day help nutritional epidemiologists and non-governmental organizations determine the populations of people that may need interventions to address nutritional deficiencies.”

The biosensor uses genetically engineered Escherichia coli (E. coli), which has a transcriptional system that responds to the level of zinc in its environment. The researchers have tuned the system to trigger the production of purple, red, or orange pigments in the presence of different zinc concentrations. Genetic machinery for producing those pigments was introduced into the E. coli.

Health workers in the field would obtain blood samples from persons suspected of having a zinc deficiency. The samples would be spun on a simple mechanical device resembling an eggbeater to separate the plasma from the blood cells. The plasma would then be placed into a test tube or other container with a pellet containing the modified E. coli. The bacterium would then produce a color indicating the zinc level.

The proof-of-concept work was reported in the journal Metabolic Engineering. The research was supported by the Bill and Melinda Gates Foundation, the National Science Foundation, and the National Institutes of Health.

— John Toon

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John Toon

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