Difference between revisions of "Team:NKU China/Notebook"

In order to make sure the efficiency of our "consumer", we should first knock out the luxS gene in our engineering bacteria GR286(a simplified strain of Bacillus amyloliquefaciens LL3). We used a markerless gene replacement method to knock out the luxS gene.

Construction of targeting vector : the upstream and downstream of luxS gene were combined by over-lapping PCR and ligated into plasmid pKSU.

pKSU-ΔluxS was transformed into GR286, and positive clones were selected.

The transformants were cultured at 42^oC with chloramphenicol to select single-crossover clones.

The single-crossover strains were then cultured in LB medium and passaged every 12 hours for 4 generations.

The last generation was cultured in medium with 5-fluorouracil to select double-crossover clones. Regretfully, we didn't get the double-crossover clones.

Transformants were cultured at 42^oC with chloramphenicol again and the single-crossover clones were selected successfully.

The single-crossover strains were then cultured in LB medium and passaged every 12 hours for 4 generations.

The last generation was cultured in medium with 5-fluorouracil to select double-crossover clones. We finally obtained our aimed strain—GR286ΔluxS.

The GR286ΔluxS strain was cultured and made competent for future use.

The lsrACDB gene from Bacillus thuringiensis was cloned and ligated to T-vector.

The T-lsrACDB was transformed into DH5α and plate was coated, and then positive clones were selected.

After restriction enzyme digestion verification, the positive clones were then sequenced. Unfortunately, the sequencing result showed some mutations inside the target gene.

The gene cloning process was repeated but there were still some mutations.

We finally decided to request the gene company to synthesize the lsrACDB gene.

This week, we started to construct another controller―supplier.

A strong promoter C2 was cloned from former kit and luxS gene was cloned from GR286.

Two segments were fused together by fusion PCR and ligated into T-vector. After that, the vector was transformed into DH5α.

Positive clones were selected by colony PCR.

4 positive strains were chosen to be cultured overnight and plasmids were extracted. After restriction enzyme digestion verification, the positive clones were sequenced.

The sequencing result showed that there was a correct strain and thus it could be used for the following experiments. We obtained the correct plasmid T-C2-luxS from DH5α. Then the fragment C2-luxS was obtained by digestion and gel extraction.

The C2-luxS fragment was ligated to linearized plasmid pWH1520, and then the ligation product was transformed into DH5α.

The plasmid pWH-C2-luxS was extracted from DH5α. To prevent the plasmid from DAM&DCM methylation, we transformed it into E.coli JM110.

The plasmid pWH-C2-luxS was extracted from JM110,and then it was treated with BamH Ⅰ methylase.

The plasmid was transformed into GR286 by electroporation.[Failed]

This week, we tried to use different voltages to transform the plasmid. Sadly, all of these attempts rendered negative results.

We considered whether the luxS gene is toxic for GR286, and the bacteria tends to reject the gene when a strong promoter is inserted upstream of it. So, we planned to use inducible promoter to reconstruct our expression vector.

The plasmid pWH1520 contains a strong xylA promoter originating from Bacillus megaterium, and transcription initiated by this promoter is xylose-inducible. Also, the gene of interest carries its own ribosome binding sequence (RBS) and translation initiation codon. Based on these points, we redesigned primers.

luxS gene was cloned from GR286 using our new primers.

The luxS fragment was purified by gel extraction, and ligated into linearized pWH1520. Then the vector was transformed into DH5α.

Positive clones were selected by colony PCR.

4 positive strains were chosen to be cultured overnight and plasmids were extracted. After restriction enzyme digestion verification, the positive clones were sequenced.

The sequencing result showed there's three positive strains. So one positive strain was chosen to be used for the following experiments. The pWH-luxS plasmid was extracted from the chosen strain. To prevent the plasmid from DAM&DCM methylation, we transformed it into E.coli JM110.

the plasmid pWH-luxS was extracted from JM110,and it was treated withBamH Ⅰ methylase.

The plasmid was transformed into GR286 by electroporation, and positive clones were selected.

We have received the product of synthetic lsrACDB gene. We first used restriction-ligation method to ligate lsrACDB to plasmid pWH1520, but we failed to select positive after several tries.

Considering that the lsrACDB gene is a large fragment (4500bp), we used ClonExpress technique to clone the gene again to improve the efficiency of ligation. The lsrACDB sequence was divided into two parts and they were cloned separately. Then the two segments were ligated to the plasmid pWH1520 and the recombinant vector was transformed into DH5α. After that, verification PCR was used to select the positive clones. However, we didn't get a good result.

We learnt a new method called circular polymerase extension cloning (CPEC) for high-throughput cloning of complex and combinatorial DNA libraries, and we decided to use this method to try to ligate our lsrACDB gene. It's encouraging that we succeeded to ligate the lsrACDB gene to the plasmid pHT-01.

Since we have already successfully constructed "supplier" and part of "consumer", we decided to measure the growth curve to explore the function of our "controller".

Cultured media of our supplier was tested for the presence of AI-2 by inducing luminescence of Vibrio harveyi reporter strain BB170.

For our consumer, we should also overexpress the lsrK and lsrFG gene for phosphorylating and degrading phosphorylated AI-2. We used ClonExpress technique to clone the two genes and ligate them to plasmid pHT-01 successfully.

We co-cultured the supplier with BB170 and tested the fluorescence intensity to explore the function of supplier. (negative result)