Combinatorial Sensor Design in Caulobacter crescentus for Selective Environmental Uranium Detection

Abstract

The ability to detect uranium (U) through environmental monitoring is of critical importance for informing water resource protection and nonproliferation efforts. While technologies exist for environmental U detection, wide-area environmental monitoring, i.e. sampling coverage over large areas not known to possess U contamination, remains a challenging prospect that necessitates the development of novel detection approaches. Herein, we describe the development of a whole-cell U sensor by integrating two functionally independent, native U-responsive two-component signaling systems (TCS), UzcRS and UrpRS, within an AND gate circuit in the bacterium Caulobacter crescentus. Through leverage of the distinct but imperfect selectivity profiles of both TCS, this combinatorial approach enabled greater selectivity relative to a prior biosensor developed with UzcRS alone; no cross-reactivity was observed with most common environmental metals (e.g, Fe, As, Cu, Ca, Mg, Cd, Cr, Al) or the U decay-chain product Th, and the selectivity against Zn and Pb was significantly improved. In addition, integration of the UzcRS signal amplifier protein UzcY within the AND gate circuit further enhanced overall sensitivity and selectivity for U. The functionality of the sensor in an environmental context was confirmed by detection of U concentrations as low as 1 μM in groundwater samples. The results highlight the value of a combinatorial approach for constructing whole-cell sensors for the selective detection of analytes for which there are no known evolved regulators.

High-resolution mapping of metal ions reveals principles of surface layer assembly in Caulobacter crescentus cells

“…Additionally, some authors have pointed to S-layers as a frontline defense against biomineralization in the hypersaline environments in which many prokaryotes are found ( Chandramohan et al., 2018 ; Kish et al., 2016 ). While the metal-ion-binding properties of SLPs have been explored in the context of using S-layers as ion traps and heavy-metal sinks ( Park and Taffet, 2019 ; Pollmann and Matys, 2007 ; Velasquez and Dussan, 2009 ; Fahmy et al., 2006 ), there remains room for exploration of the role of metal ions in S-layer biogenesis.…”

Characterization of Bacterial and Fungal Assemblages From Historically Contaminated Metalliferous Soils Using Metagenomics Coupled With Diffusion Chambers and Microbial Traps

“…Interestingly, there were several other taxa that also were significantly enriched only in the highest contaminated soils, as indicated by differential analysis where the low, medium and high levels of soil THg contamination was statistically evaluated relative to the reference soils; the taxa found at higher abundances are indicated by parenthesis and red arrows in Supplementary Figure S3. Surprisingly, these did not include any of the 9 Hg resistant genera as reported by Rani et al (2015), but did include a plethora of other bacterial genera that are well-known to resist uranium such as Rhodanobacter and Caulobacter, respectively (Kostka et al, 2012;Chung et al, 2014;Park and Taffet, 2019). It is highly likely that these genera possess ecologically beneficial traits that facilitate their survival under the tested metalliferous soils and further research on these bacterial genera is recommended for environmental remediation and development of biosensors.…”

Molecular Mechanisms Underlying Bacterial Uranium Resistance

“…On its turn, the phosphorylated RR regulates the expression of metal resistance genes, but often also autoregulates the expression of the TCS. In C. crescentus NA1000, two uranium-responsive TCSs have been identified by analyzing transcriptomic and proteomic data after exposure to non-toxic uranium concentrations ( Hu et al, 2005 ; Yung et al, 2014 ; Park et al, 2017 ; Park and Taffet, 2019 ). UrpRS ( u ranium r esponsive p hytase regulator and sensor, respectively, CCNA_01362 + 01363) was found to regulate a phytase gene (CCNA_01353) that confers uranium resistance when phytate is provided as the sole phosphate source ( Yung et al, 2014 ; Park and Taffet, 2019 ).…”