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Caulobacter crescentus as a Whole-Cell Uranium Biosensor ^,

Department of Developmental Biology, Beckman Center, Stanford University School of Medicine, Stanford, California 94305,¹ Lawrence Berkeley National Laboratory, Berkeley, California 94720²

Received 10 July 2007/ Accepted 19 September 2007

We engineered a strain of the bacterium Caulobacter crescentus to fluoresce in the presence of micromolar levels of uranium at ambient temperatures when it is exposed to a hand-held UV lamp. Previous microarray experiments revealed that several Caulobacter genes are significantly upregulated in response to uranium but not in response to other heavy metals. We designated one of these genes urcA (for uranium response in caulobacter). We constructed a reporter that utilizes the urcA promoter to produce a UV-excitable green fluorescent protein in the presence of the uranyl cation, a soluble form of uranium. This reporter is specific for uranium and has little cross specificity for nitrate (<400 µM), lead (<150 µM), cadmium (<48 µM), or chromium (<41.6 µM). The uranium reporter construct was effective for discriminating contaminated groundwater samples (4.2 µM uranium) from uncontaminated groundwater samples (<0.1 µM uranium) collected at the Oak Ridge Field Research Center. In contrast to other uranium detection methodologies, the Caulobacter reporter strain can provide on-demand usability in the field; it requires minimal sample processing and no equipment other than a hand-held UV lamp, and it may be sprayed directly on soil, groundwater, or industrial surfaces.

Published ahead of print on 28 September 2007.

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