Bioluminescent-bioreporter integrated circuits form novel whole-cell biosensors

Whole-cell biocomputing

The ability to manipulate systems on the molecular scale naturally leads to speculation about the rational design of molecular-scale machines. Cells might be the ultimate molecular-scale machines and our ability to engineer them is relatively advanced when compared with our ability to control the synthesis and direct the assembly of man-made materials. Indeed, engineered whole cells deployed in biosensors can be considered one of the practical successes of molecular-scale devices. However, these devices explore only a small portion of cellular functionality. Individual cells or self-organized groups of cells perform extremely complex functions that include sensing, communication, navigation, cooperation and even fabrication of synthetic nanoscopic materials. In natural systems, these capabilities are controlled by complex genetic regulatory circuits, which are only partially understood and not readily accessible for use in engineered systems. Here, we focus on efforts to mimic the functionality of man-made information-processing systems within whole cells.

An integrated CMOS microluminometer for low-level luminescence sensing in the bioluminescent bioreporter integrated circuit

We report an integrated CMOS microluminometer for the detection of low-level bioluminescence in whole cell biosensing applications. This microluminometer is the microelectronic portion of the bioluminescent bioreporter integrated circuit (BBIC). This device uses the n-well/p-substrate junction of a standard bulk CMOS IC process to form the integrated photodetector. This photodetector uses a distributed electrode configuration that minimizes detector noise. Signal processing is accomplished with a current-to-frequency converter circuit that forms the causal portion of the matched filter for dc luminescence in wide-band white noise. Measurements show that luminescence can be detected from as few as 4 x 10(5) cells/ml.

A bioluminescent whole-cell reporter for detection of 2, 4-dichlorophenoxyacetic acid and 2,4-dichlorophenol in soil

A bioreporter was made containing a tfdRP(DII)-luxCDABE fusion in a modified mini-Tn5 construct. When it was introduced into the chromosome of Ralstonia eutropha JMP134, the resulting strain, JMP134-32, produced a sensitive bioluminescent response to 2, 4-dichlorophenoxyacetic acid (2,4-D) at concentrations of 2.0 microM to 5.0 mM. This response was linear (R(2) = 0.9825) in the range of 2.0 microM to 1.1 x 10(2) microM. Saturation occurred at higher concentrations, with maximal bioluminescence occurring in the presence of approximately 1.2 mM 2,4-D. A sensitive response was also recorded in the presence of 2,4-dichlorophenol at concentrations below 1.1 x 10(2) microM; however, only a limited bioluminescent response was recorded in the presence of 3-chlorobenzoic acid at concentrations below 1.0 mM. A significant bioluminescent response was also recorded when strain JMP134-32 was incubated with soils containing aged 2,4-D residues.

Online and in situ monitoring of environmental pollutants: electrochemical biosensing of cadmium

Online sensitive monitoring of gene expression is essential for understanding microbial life and microbial communities, especially under stress-inducing conditions, such as the presence of environmental pollutants. We describe here a novel use of promoter-based electrochemical biosensing for online and in situ monitoring of gene expression in response to pollutants. As a model system, we used a cadmium-responsive promoter from Escherichia coil fused to a promoterless lacZ gene, which was monitored using an electrochemical assay of beta-galactosidase activity. This whole-cell biosensor could detect, within minutes, nanomolar concentrations of cadmium in water, sea water and soil samples, and it can be used for continuous online and in situ monitoring.

Development and characterization of a lux-modified 2,4-dichlorophenol-degrading Burkholderia sp. RASC

lux-marked biosensors for assessing the toxicity and bioremediation potential of polluted environments may complement traditional chemical techniques. luxCDABE genes were introduced into the chromosome of the 2,4-dichlorophenol (2,4-DCP)-mineralizing bacterium, Burkholderia sp. RASC c2, by biparental mating using the Tn4431 system. Experiments revealed that light output was constitutive and related to cell biomass concentration during exponential growth. The transposon insertion was stable and did not interrupt 2,4-DCP-degradative genes, and expression of luxCDABE did not constitute a metabolic burden to the cell. A bioluminescence response was detectable at sublethal 2,4-DCP concentrations: at < 10.26 microg ml(-1), bioluminescence was stimulated (e.g. 218% of control), but at concentrations >60 microg ml(-1) it declined to < 1%. Investigating the effect of [14C]-2,4-DCP concentration on the evolution of 14CO2 revealed that, for initial concentrations of 2.5-25 microg ml(-1), approximately equals 55% of the added 14C was mineralized after 24 h compared with <1% at 50 and 100 microg ml(-1). Inhibition of 2,4-DCP mineralization between 25 and 50 microg ml(-1) corresponded well to the EC50 value (33.83 microg ml(-1)) obtained from bioluminescence inhibition studies. lux-marked RASC c2 may therefore be used as a functionally (i.e. 2,4-DCP degrader) and environmentally relevant biosensor of toxicity and biodegradation inhibition.

Green fluorescent protein in the design of a living biosensing system for L-arabinose

Analysis of monosaccharides is typically performed using analytical systems that involve a separation step followed by a detection step. The separation step is usually necessary because of the high degree of structural similarity between different monosaccharides. A novel sensing system for monosaccharides is described here in which living bacteria were designed to detect a model monosaccharide, L-arabinose, without the need for a separation step. In such sensing systems, analytes are detected by employing the selective recognition properties found in certain bacterial proteins. These systems are designed so that a reporter protein is expressed by the bacteria in response to the analyte. The concentration of the analyte can be related to the signal generated by the reporter protein. In the sensing system described here, the green fluorescent protein (GFP) was used as the reporter protein. L-Arabinose concentrations can be determined by monitoring the fluorescence emitted by the bacteria at 509 nm after excitation of GFP at 395 nm. The system can detect L-arabinose at concentrations as low as 5 x 10(-7) M and is selective over D-arabinose, the stereoisomer of the analyte, as well as over a variety of pentose and hexose sugars.

Construction of a bioluminescent reporter strain To detect polychlorinated biphenyls

A bioluminescent reporter strain, Ralstonia eutropha ENV307(pUTK60), was constructed for the detection of polychlorinated biphenyls by inserting the biphenyl promoter upstream of the bioluminescence genes. In the presence of a nonionic surfactant, which enhances the solubility of chlorinated biphenyls, bioluminescence was induced three- to fourfold over background by biphenyl, monochlorinated biphenyls, and Aroclor 1242. The minimum detection limits for these compounds ranged from 0.15 mg/liter for 4-chlorobiphenyl to 1.5 mg/liter for Aroclor 1242.