Aim of experiment
Based on J33201 part, a biosensor pSB1C3-pArsR-RBS-GFP(K3153000) was constructed to detect arsenite(As3+) in water and contributed to this well-characterized part.
Methods
1. Growth curve of E.coli containing part K577881 in different concentrations of arsenite(As3+)
Constructed plasmid pSB1C3-pArsR-GFP containing J33201 part was transformed into E.coli DH5α strain. Single colony was selected to inoculate LB broth containing chloramphenicol and cultured overnight. Then overnight culture was inoculated in the fresh LB medium containing 34 μg/ml chloramphenicol at a ratio of 1:100, mixed well and divided into tubes. Different concentrations of arsenite (As3+) solutions were added into the test tubes, respectively. The final concentration of arsenic was (0, 5ppb, 10ppb, 50ppb, 100ppb, 500ppb, 1ppm, 5ppm, 10ppm, 50ppm and 100ppm). Samples were collected at different time points of 0 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h and 16 h. OD600 values were measured by the Multiskan Spectrum Microplate Reader.
2. GFP expression of E.coli under the control of J33201 induced by different concentration of arsenite (As3+)
Overnight cultured bacterial solution was inoculated in LB broth containing chloramphenicol at 1:50 to expand the culture. When OD600 reached 0.4-0.6, experiments were performed . Different concentrations of arsenite were added into the test tube, respectively. The final concentration of arsenic was 0, 5 ppb, 10 ppb, 50 ppb, 100 ppb, 500 ppb, 1 ppm, 5 ppm, 10 ppm, 50 ppm, 100 ppm.
(1) Samples were collected at 16 h. GFP fluorescence intensity (485 nm excitation/ 528 nm emission) and OD600 value were measured at the same time. The bacteria were centrifuged, and the pellets were was observed and photographed under Blue Light Gel Imager.
(2)Samples were collected at different time points of 0 h, 2 h, 4 h, 6 h and 16 h. GFP fluorescence intensity (485 nm excitation/ 528 nm emission) and OD600 value were measured at the same time.
Results
Fig.1 showed that bacteria growth was not affected from 5 ppb to 10 ppm of arsenite solution (As3+). However, when the concentration of arsenite increased to 50 ppm, the growth of the bacteria was seriously inhibited, suggesting the toxictity to cells at this concentration.
Fig.1 Growth curve of E.coli in different concentration of arsenic (As3+).
As shown in Fig.2, our biosensor based on J33201 part is very sensitive to arsenite(As3+) and the fluoresence signal was be detected at 50 ppb arsenite. Significant dose-dependent effect was observed from 50 ppb to 1 ppm arsenite. The threshold of this biosensor is 10 ppm. As the arsenite concentration increased to 50 ppm, it does’t work because of the toxicity to cell at thisconcentration.
(Fig.2a)
(Fig.2b)
Fig.2 GFP expression of E.coli under the control of J33201 in different concentration of arsenite (As3+).
As shown in Fig.3, our biosensor by J33201 reacted rapidly in arsenite solution. After 4 h following arsenite treated, the corresponding fluorescence signal was detected at 100 ppb. As time increases, a weak signal can be detected at 50ppb, indicating that the biosensor can work within 4 hours.
Fig.3 GFP expression of E.coli in different concentration of arsenite (As3+) at different time points under the control of J33201.
Summary
our biosensor constructed on the basis of J33201 is sensitive and fast. The biosensor can detect 100ppb-10ppm arsenite (As3+) in water within 4 hours. With the extension of time, the minimum detection limit can reach 50 ppb.
Reference
Anal Bioanal Chem. 2011 May;400(4):1031-9. Epub 2011 Mar 27.