Team:Hong Kong HKUST/pneumosensor/results/module one

The two-component regulatory system in S. pneumoniae, consisting of the receptor ComD and its response regulator ComE was to be used in detecting the autoinducer molecule, competence-stimulating peptide (CSP) and so detect S. pneumoniae populations correspondingly.

Tag protein
We engineered in a FLAG protein tag in the 3’ end of ComD by including the sequence in comD extraction primer.
Forward primer to extract comD to clone into PSB1C3: TCTGGAGAATTCGCGGCCGCTTCTAGATGGATTTATTTGGATTTGGGACGG
[6’cap][20’ RFC10 prefix][25’ Streptoccocus pneumoniae/NCTC7465/comD]

3’ primer to extract comD with engineered FLAG tag gene sequence: GCCGGACTGCAGCGGCCGCTACTAGTATTATTACTTGTCGTCATCGTCTTTGTAGTCTCATTCAAATTCCCTCTTAAATCTAATGAT
[6’ cap][21’ RFC10 suffix][6’ reverse complement stop codon][25’ reverse complement FLAG protein ][30 reverse complement Streptoccocus pneumoniae/NCTC7465/comD]


comE was extracted from pKHS-come kindly sent to us by ??. Extraction was done using the following primers:
Forward primer to extract comE to clone into pSB1C3: TCTGGAGAATTCGCGGCCGCTTCTAGATGAAAGTTTTAATTTTAGAAGATG
[6’ cap][20’ RFC10 prefix][25’ Streptoccocus pneumoniae/NCTC7465/comE]
Reverse primer to extract comE to clone into pSB1C3: GCCGGACTGCAGCGGCCGCTACTAGTATCACTTTTGAGATTTTTTCTCTAA
[6’ cap][21’ RFC10 suffix][24’reverse complement Streptoccocus pneumoniae/NCTC7465/comE]

come contained an illegal SpeI site, so we designed primers for site-directed mutagenesis:
Mutagenesis forward primer: CGCTATTATCGTCTTTATCACTAGCCGATCAGAGTTTGCGACTCTAAC

Mutagenesis reverse primer: GTTAGAGTCGCAAACTCTGATCGGCTAGTGATAAAGACGATAATAGCG

However, site-directed mutagenesis attempts were unsuccessful, so the gene was extracted in two parts using (i) come forward primer & mutagenesis reverse primer; (ii) come reverse primer & mutagenesis forward primer. The two fragments were then combined through Gibson Assembly.

Backbone pSB1C3 was used for PCelA and Phelicase construct. PCelA / Phelicase gene was fused with BBa_E0240, which contains a medium RBS (BBa_B0032), GFP (BBa_E0040) and double terminator (BBa_B0015). The purpose of this GFP generator is to indicate the functionality of PCelA and Phelicase in the presence and absence of ComX protein. BBa_E0240 was obtained from 2014 iGEM distribution kit. The bacterial strain of E.coli used is DH10B.

PCelA / Phelicase gene
PCelA and Phelicase gene was cloned from the genomic DNA of E.Coli strain NCTC7465 by PCR using Vent Polymerase. The difference between these two promoters is the whole sequence of Phelicase was obtained from Wellcome Trust Sanger Institute, a British genomics and genetics research institute. (https://www.sanger.ac.uk/)

PcelA Forward primer: TTTCTGTCTAGAGTTGACCAAGGAAGACTATTTTGC

PcelA Reverse primer: GCCGGACTGCAGCGGCCGCTACTAGTAATTTTCTCCTCTCTTAGATTATTCGTAAGAGG

Phelicase Forward primer: TTTCTGTCTAGAGTGGACTTGGCCGTCCTCT

Phelicase Reverse primer: GCCGGACTGCAGCGGCCGCTACTAGTAGACGTTCTTCTTCTGTTAATTCATTCTCAG

Assembly comX and comW construct contain 3 parts that needs to be assembled: K880005 which contains constitutive promoter and RBS, comX engineered with C-myc tag / comW engineered with FLAG tag, and a double terminator in pSB1C3 backbone. Promoter, RBS, comX engineered with C-myc tag, and double terminator were combined using traditional digestion and ligation method. The ligation product was confirmed by digestion check and sequencing.

Combox construct also contains 3 parts that need to be assembled: PcelA/Phelicase promoter, BBa_E0240 which contains RBS, GFP and double terminator, and pSB1C3 backbone. All three parts were combined using traditional digestion and ligation method. The final ligation product was confirmed by digestion check and sequencing.

Characterization
RPU (Relative promoter unit) and leakage will be measured as a characterization of 100 base pairs combox promoter (PcelA), and 160 base pairs combox promoter (Phelicase). For combox promoter characterization, ComX generator construct which contain K880005, comX gene, and B0015, is ligated with PcelA / Phelicase construct which contain combox promoter and GFP generator. In order to characterize the two combox promoters, ComX generator-combox construct was migrated from pSB1C3 to pSB3K3. RPU are measured with J23100 Andersen family promoter as a reference promoter.