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The fixed-gain bio-amplifier

The tunable biological amplifier (Fig. 1) comprises three modular terminals--the input, the output and a gain-tuning input. The device can continuously process the input transcriptional signal with an externally tunable gain (the amplification ratio of the changes in output to input) control.[1]

Figure 1. The composition of tunable biological amplifier. Transcription input can be amplified through the amplifier.

At first, we construct the fixed-gain amplifier (Fig. 2) for the prework. In order to reduce the impact of exotic microorganisms' colonizations in the intestine and to accelerate the secretion of IL-10 and myrosinase, we found a gain-tunable transcription amplifier in Pseudomonas syringae to tune amplifier the input signal.

To verify the fixed-gain amplification(Fig. 2) capability, we integrated the T7 promoter as the input of the fixed-gain amplifier with GFP as the output. When the transduced transcriptional input from the T7 promoter was connected to our amplifier, the resulting output signal amplitude and dynamic range increased significantly as well as the response sensitivity to the inducer (Fig 3.).

Figure 2. Diagram for fixed-gain amplifier in pCDFDuet-1 plasmid. T7 promoter, the gene downstream of this promoter will be transcribed when there is T7 RNA polymerase. lacO, the sequence represses the nearby promoter when there is NO inducer (e.g. IPTG). RBS, ribosome binding site. hrpR, hrpS, the activator proteins. P_hrpL, a promoter which can be induced by the ultrasensitive high-order co-complex hrpRS. GFP, green fluorescent protein.

Figure 3. Responses of the GFP without fixed-gain amplification (V-GFP) and with fixed-gain amplification (V-AM). The cells are induced by 5 varying concentrations of IPTG (0, 10^-6 M, 10^-5 M, 10^-4 M, 10^-3 M) after 4 and 6 hours (A, 4h; B, 6h).

Method We transformed 3 different vectors into E. coli BL-21 competent cell. Amplifier and GFP sequences are inserted into pcdfDuet-1 vectors which are called V-AM and V-GFP. Empty vectors with amplifier or GFP were named VE, VE-GFP and VE-AM. After vector transformation, we grow transformed competent cells on the LB plates with streptomycin, once we get colonies, we culture single colony in 5 ml LB medium overnight at 37oC. Next day, we wash bacteria by 1ml PBS and measure the cell growth pattern by photocytometer. In order to read for the fluorescent signals, we use LB-S (LB with streptomycin) to dilute bacteria and add them into the Corning™ 3916 black 96-well plate with OD600=0.025 per well. Five different Isopropyl-beta-D-thiogalactopyranoside (IPTG) concentrations (0, 10-3 M, 10-4 M, 10-5 M and 10-6 M) were used to induce the T7 promoter activation and induce for 4 or 6 hours. After IPTG induction, the Enzyme Labeling Instrument were used to detect the green fluorescent signal. The excitation wavelength is 485 nm with the absorption wavelength 525 nm.

In conclusion, the amplifier achieves the desired effect, and the amplification gain is about 2 times. Comparing other amplifiers, this value is still low. In addition, we find that the gene expression process is accelerated with the amplifier, the reporter GFP usually reaching its saturation value after about 4 hours' induction.

Reference

[1]Jovanovic,M., James,E.H., Burrows,P.C., Rego,F.G.M., Buck,M. and Schumacher,J. (2011) Regulation of the co-evolved HrpR and HrpS AAA+ proteins required for Pseudomonas syringae pathogenicity. Nat. Commun., 2:177.

Sequence and Features