Caulobacter crescentus as a Whole-Cell Uranium Biosensor

APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Dec. 2007, p. 7615–7621 0099-2240/07/$08.00⫹0 doi:10.1128/AEM.01566-07 Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Vol. 73, No. 23

Caulobacter crescentus as a Whole-Cell Uranium Biosensor䌤† Nathan J. Hillson,1 Ping Hu,2 Gary L. Andersen,2 and Lucy Shapiro1* Department of Developmental Biology, Beckman Center, Stanford University School of Medicine, Stanford, California 94305,1 and 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 (