Team:Yale/Our Project/Notebook/Week 6

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iGEM Yale

Monday 7/12--Copper growth assay of pSB74 transformants & continued ligation work

Measured the OD of the overnight LE392 cultures and found that the LE392 containing pSB74 had an OD of 0.58 while the untransformed culture had an OD of 0.87. Wanted to let the transformed culture grow a while with IPTG prior to beginning of assay (to allow time for protein expression), but didn't want either culture to overgrow in the mean time, so diluted each as follows:
To 1 mL of the untransformed solution added 4 mL of plain LB, while to 3 mL of the transformed LE392 added 2 mL of LB with Amp and 10 uL of IPTG, bringing the IPTG concentration to the desired 2 mM. Let diluted cultures grow another hour at 37˚C to reach mid-log phase.
Following the second growth period, measured the OD of the untransformed culture as 0.75 while the OD of the pSB74 transformants was 0.88, but it was diluted to 0.75.
Finally the solutions were loaded into the 96-well plate as follows, with each row having 12 wells and copper concentration decreasing left to right as before.

Miniprep and sequencing of attempt #4 transformants

Using the vacuum manifold protocol miniprepped the cultures grown up from the sixteen colonies (#9-#24) that resulted from the 4th ligation attempt.
Nanodropped three to get a sense of concentration and found that the average was 65.3 ng/uL
Prepared all sixteen samples for sequencing, taking 4 uL of each miniprep, 2 uL of 4 uM VF2 primer, and 12 uL of water.

Digest of miniprepped attempt #4 products

Digested each of the ligation products with EcoRI to linearize them prior to running them on a gel and determining their size. Each digestion reaction was composed of 5 uL of EcoRI buffer, 0.5 uL 100x BSA, 15 uL of plasmid DNA, 3.6 uL EcoRI, and 25.9 uL of water and was run overnight in the 37˚C incubator.

Colony PCR of ligation attempt #4 transformants

Ran colony PCR for each of the sixteen transformants, relying on the index plates as a cell source. Spotted cells in 20 uL of water to lyse them, then added 1 uL of the resulting solution to a PCR tube. To each tube also added 2 uL of VF2 primer (10 mM), 2 uL of VR primer (10 mM), 10.8 uL water, 4 uL 5x Phusion Buffer, 0.6 uL of DMSO, 0.4 uL dNTPs, and 0.2 uL of Phusion polymerase. Ran the reactions on the "VR" thermocycler protocol

Wetlab work for this day is also recorded on pages 59 and 62-64 of the hard copy lab notebook.

Tuesday 7/13--Transformant Copper growth assay, ligation attempt #4 results, and copper removal assay prep

Looked at results of the previous day's assay and saw that the presence of pSB74 actually decreased the copper tolerance of the LE392. Maybe the effort associated with protein production actually weakens the cell's ability to deal with the copper?
Spotted each culture from the 96-well plate onto an agar plate (LB and ampicillin in the case of transformants, plain LB in the case of the untransformed) and put in incubator to see if it grows.

Ran 1.0% agarose gels of both the colony PCR reactions and EcoRI digestion of minipreps. Gels contained 10 uL of ethidium bromide and were run at 90 V with a 1 kb ladder, but the power source malfunctioned and turned off at some point, so the gel sat for an unknown amount of time. Restarted power source, let run, and then visualized the gels
Digestion of miniprep shows that all ligation efforts failed--had they succeeded there would have been fragments at 7.8 kb, but as the gel below shows, all the samples run at slightly over 3 kb (ladder rungs are 500 bp, 1 kb, 1.5 kb, 2 kb, 3 kb, 4 kb, 5 kb, 6 kb, 8 kb, & 10 kb).
Efforts to visualize the colony PCR gel failed entirely--maybe forgot to add ethidium bromide? But given above results, it's a moot point.

Want to run an assay measuring whether pSB74 transformants remove copper(II) from their surroundings. If had a large bacterial culture with an intermediate CuSO₄ concentration (say 500 uM), could periodically remove small aliquots, centrifuge out the cells, and spectrophotometrically determine the copper content.
Need to determine what wavelength should be used to monitor copper concentration and create a calibration curve relating absorbance at that wavelength to copper concentration.
Start by making serial dilutions of CuSO₄ in LB. Made samples of 0.1 M, 10 mM, 1 mM, 100 uM, 10 uM, 1 uM and 0.1 uM concentrations.
While spectrum had no clear peak, the CuSO₄ did absorb strongly at 700 nm compared to just LB, so chose that as wavelength to monitor. Attempted to establish curve, but got the odd result that the 10 uM absorbed orders of magnitude more than the 100 uM. Will redo dilutions and try again another day.
Inoculated 5 mL liquid cultures of LE392, both with and without pSB74, adding 5 uL of 1000x ampicillin to the transformant culture. Let grow overnight on shaker at 37˚C.

Wetlab work for this day is also recorded on pages 65-67 of the hard copy lab notebook.