Team:Cambridge/Protocols/Electrocompetentcells

From 2012.igem.org

Parts for a reliable and field ready biosensing platform

Implementation of biosensors in real world situations has been made difficult by the unpredictable and non-quantified outputs of existing solutions, as well as a lack of appropriate storage, distribution and utilization systems. This leaves a large gap between a simple, functional sensing mechanism and a fully realised product that can be used in the field. We aim to bridge this gap at all points by developing a standardised ratiometric luciferase output in a Bacillus chassis. This output can be linked up with prototyped instrumentation and software for obtaining reliable quantified results. Additionally, we have reduced the specialized requirements for the storage and distribution of our bacteria by using Bacillus' sporulation system. To improve the performance of our biosensing platform we have genetically modified Bacillus’ germination speed. Lastly, we demonstrated the robustness of our system by testing it with a new fluoride riboswitch, providing the opportunity to tackle real life problems.

One minute tour! :)

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Contents

Judging Form

  • Please help the judges by filling out this form. Tell them what medal you think you deserve and why. Tell them which special prizes you should win. Help them find your best parts. Show them how you thought about the safety of your project. Helping the judges will help you too.

  • Team: Cambridge
  • Region: Europe
  • iGEM Year:2012
  • Track:Foundational Advance
  • Project Name:Parts for a reliable and field ready biosensing platform
  • Project Abstract: Implementation of biosensors in real world situations has been made difficult by the unpredictable and non-quantified outputs of existing solutions, as well as a lack of appropriate storage, distribution and utilization systems. This leaves a large gap between a simple, functional sensing mechanism and a fully realised product that can be used in the field.

    We aim to bridge this gap at all points by developing a standardised ratiometric luciferase output in a Bacillus chassis. This output can be linked up with prototyped instrumentation and software for obtaining reliable quantified results. Additionally, we have reduced the specialized requirements for the storage and distribution of our bacteria by using Bacillus' sporulation system. To improve the performance of our biosensing platform we have genetically modified Bacillus’ germination speed. Lastly, we demonstrated the robustness of our system by testing it with a new fluoride riboswitch, providing the opportunity to tackle real life problems.

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iGEM Medals for non-software teams

  • We believe our team deserves the following medal:
    • Bronze
    • Silver
    • √Gold

Because we met the following criteria (check all that apply and provide details where needed)

Requirements for a Bronze Medal

  • √Register the team, have a great summer, and plan to have fun at the Regional Jamboree.
  • √Successfully complete and submit this iGEM 2012 Judging form.
  • √Create and share a Description of the team's project using the iGEM wiki and the team's parts using the Registry of Standard Biological Parts.
  • √Plan to present a Poster and Talk at the iGEM Jamboree.
  • √Enter information detailing at least one new standard BioBrick Part or Device in the Registry of Standard Biological Parts. Including:
    • √Primary nucleaic acid sequence
    • √Description of function
    • √Authorship
    • Safety notes, if relevant.
    • √Acknowedgment of sources and references
  • √Submit DNA for at least one new BioBrick Part or Device to the Registry.

Additional Requirements for a Silver Medal

  • √Demonstrate that at least one new BioBrick Part or Device of your own design and construction works as expected; characterize the operation of your new part/device.
  • √Enter this information and other documentation on the part's 'Main Page' section of the Registry
    Part Number(s): BBa_K911004

Additional Requirements for a Gold Medal: (one OR more)

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iGEM Prizes

All teams are eligible for special prizes at the Jamborees. more... To help the judges, please indicate if you feel you should be evaluated for any of the following special prizes:

  • √Best Human Practice Advance
  • √Best Experimental Measurement
  • Best Model

Please explain briefly why you should receive any of these special prizes:

Best Human Practice Advance:

We feel that we deserve this prize for three reasons:

  1. We explored the impacts, *both positive and negative*, of synthetic biology as a solution to real world problems, through interviewing professionals working in a relevant field, namely the impact of arsenic water contamination in Bangladesh.
  2. We recognized existing problems with the way the current direction of synthetic. On going through the registry we found that most of the characterization data for biosensing parts is often neither comparable nor replicable. We have worked to solve this issue, for example with our ratiometric dual channel output.
  3. *Our project doesn’t stop here*, in Chanel number 6 (Team:Cambridge/HumanPractices/FutureDirections) we considered the future implications and technological applications of our project, as well as the means by which it could be improved by subsequent users. We feel that the end to an iGEM project should not be the conclusion of an idea, but the start of it.

Best BioBrick Measurement Approach:

It is absolutely vital that a quantitative, numerical, robust, and flexible measurement approach exists to relay information to a user that is an accurate representation of the input processed by a biological device. Working from these principles, the following was done:

  1. We designed and built Biologger, a *cheap, arduino-based, fully functional automatic rotary device* that has an incorporated ratiolumnometer
  2. Our project is entirely open-sourced and open-platform. We have published source code for the two applications which serve to operate the device, one for PCs and the other for Android devices, as well as the open source circuit design that provides this ratiometric reading. Furthermore, the Android app is able to receive its data wirelessly, which we feel is a great advance in BioBrick measurement.
  3. Our dual-channel luciferase reporter was successfully tested with a dilution series of E.coli transformed with the Lux Operon (under pBAD) biobrick (Part BBa_K325909) of the Cambridge iGEM 2010 team. It can detect, with good accuracy, both different light intensities, as well as the percentages of blue or orange frequencies in a sample.
  4. Our device was successfully tested using artificial light to detect different frequencies (colours) as well.

Having done all the above, we believe that this fully open-sourced instrumentation kit (mechanical) chassis, electronics, software code), estimated at *$35.00* (or $85.00 if a Bluetooth modem is required), is a complete BioBrick measurement solution for any and all BioBricks with a light output.

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Team_Parts

To help the judges evaluate your parts, please identify 3 of your parts that you feel are best documented and are of the highest quality.

  • Best new BioBrick part (natural)
    BBa_K911003
    Best new BioBrick part (engineered)
    BBa_K911004
  • Best improved part(s): None

List any other parts you would like the judges to examine:BBa_K911001, BBa_K911009, BBa_K911008

Please explain briefly why the judges should examine these other parts:

  • Magnesium Sensitive Riboswitch BBa_K911001
    As a riboswitch sensing construct, this part is an entirely new type of biosensor (along with the fluoride construct) that could potentially change the way we think about designing input genetic circuits. Unlike the fluoride riboswitch, it is a derepression system and therefore serves to demonstrate the principle that riboswitches can be used regardless of whether they turn on or off their reporter.
  • Fluorescent ratiometric construct for standardizing promoter output BBa_K911009
    Fluorescence is a major cornerstone for biosensors in the registry, however, most parts do not involve the use of a ratiometric output, which has been shown in the literature to provide much more reliable and meaningful data. This part not only furthers the development of ratiometric measurements in molecular biology but due to the choice of promoters and terminators it can be used to characterize the difference in activity between E. coli and B. Subtilis
  • Fast Germination (B. subtilis) BBa_K911008
    This part is entirely novel for the registry and fully utilizes the recombination machinery inherent in the Bacillus chassis. Have spores that can germinate at a faster rate is certainly a worthy achievement and could help with experiments with B. Subtilis that any future iGEM teams may wish to perform.

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iGEM Safety

For iGEM 2012 teams are asked to detail how they approached any issues of biological safety associated with their projects.

The iGEM judges expect that you have answered the four safety questions Safety page on your iGEM 2012 wiki.

Please provide the link to that page: Page name: Team:Cambridge/Safety

Attribution and Contributions

For iGEM 2012 the description of each project must clearly attribute work done by the team and distinguish it from work done by others, including the host labs, advisors, and instructors.

Please provide the link to that page, or comments in the box below: Page name: Team:Cambridge/Attributions

Comments

If there is any other information about your project you would like to highlight for the judges, please provide a link to your wiki page here: Team:Cambridge/Overview/DesignProcess

This protocol was adapted from Openwetware.org.

Growing Electrocompetent Cells

Originally from Sambrook and Russell's "Molecular Cloning: A Laboratory Manual" Third Edition.

(Note: once the cells are grown and have been placed in the first ice bath, you do not want the temperature of the sample to rise above 4 °C at any point. Therefore, many of the instructions are given with this in mind; always think ahead to the next step and to how you are going to keep your cells from warming up. This includes prechilling tubes and keeping all wash materials and samples on ice.)

Fundamental idea of protocol

The main idea here is to get a very HIGH DENSITY (hence the centrifugation), UNCONTAMINATED (hence all the autoclaving), culture of cells in a completely SALT FREE solution (this is to prevent arcing in the electroporation kit). Depending on what OD600 readings are taken, more centrifugation steps might be needed in smaller volumes of glycerol/GYT in the later stages of the protocol.

Materials

GYT (glycerol, yeast extract, tryptone)

• 10%(v/v) glycerol
• 0.125% (w/v) yeast extract
• 0.25% (w/v) tryptone

DI water
10% Glycerol

Autoclave beforehand

1x250ml flask (or use new plastic one)

2x 475ml LB in 1L flasks

1.2L DI water in 1L bottles (make more than this...)

4 x 250ml flat bottomed centrifuge tubes

GYT

10% Glycerol

(For the GYT and Glycerol, only small amounts are needed but it's always useful to have sterile stock so get some 1L bottles out)

Eppendorfs for the 40μl aliquots

Method

Important: All steps in this protocol should be carried out aseptically. Get lots of ice ready and make sure you leave enough time to cool things down from the autoclave (especially the water - the importance of this is obviously dependent on your schedule)

  • Inoculate:

Prepare flask containing 50 ml of LB medium. Pick up a single colony of cells from plate (using a sterile toothpick) and swirl around inside flask. Incubate the culture overnight at 37°C with vigorous aeration (250 rpm in a rotary shaker).

  • Dilute and incubate:

Inoculate two aliquots of 475 ml of prewarmed LB medium in separate 2-liter flasks with 25 ml of the overnight bacterial culture. Incubate the flasks at 37°C with agitation (300 cycles/min in a rotary shaker). Measure the OD-600 every twenty minutes (this step will take around 1.5-2 hrs).

  • Rapidly cool culture:

Once the OD-600 of the culture reaches 0.5, rapidly transfer the flasks to the pre-made ice-water bath for 15-30 minutes. Swirl the culture occasionally to ensure that cooling occurs evenly. In preparation for the next step, place the centrifuge bottles in the ice-water bath as well.

Note: After this point, do not let your cells warm up past 4°C

Note: When harvesting cells by decanting, be very careful to not disturb the pellet-- this could result in a much lower yield. If necessary, aspirate instead of decant the supernatant. Get someone to show you how to aspirate. Also, if the pellet seems loose, sometimes it is helpful to re-spin the cells down.

"Note: A standalone centrifuge is required during this protocol and the correct rotor must be selected"

  • Centrifuge 1:

Transfer the cultures to 4 250ml ice-cold centrifuge bottles (in 200ml volumes - i.e. discard 200ml). Harvest the cells by centrifugation at 1000g (2500 rpm) for 15 minutes at 4°C. Decant the supernantant and resuspend the cell pellets in 200 ml of ice-cold DI water (200ml per centrifuge bottle i.e. a 1:1 suspension).

  • Centrifuge 2 (water):

Harvest the cells by centrifugation at 1000g for 20 minutes at 4°C. Decant the supernatant and resuspend the cell pellets in 100 ml ice-cold DI water (per tube). If you like you can now combine two tubes into one - as long as the centrifuge is always balanced. You will now have 2 x 200ml suspensions to be centrifuged.

  • Centrifuge 3 (water):

Harvest the cells by centrifugation at 1000g for 20 minutes at 4°C. Decant the supernatant and resuspend the cell pellet in 10 ml ice-cold 10% glycerol.

    • To spin down your pellet in 10 ml, transfer your suspensions into 15-ml Falcon tubes instead of using the round-bottom tubes. A smaller centrifuge can now be used
  • Centrifuge 4 (glycerol):

Harvest the cells by centrifugation at 1000g for 20 minutes at 4°C. Carefully decant the supernatant and use a Pastteur pipette attached to a vacuum line to remove any remaining drops of buffer (A normal pipette will also do - DO NOT POUR the supernatant or you WILL lose culture).

  • Resuspend in GYT:

Resuspend in 1 ml ice cold GYT. This is best done by gently swirling rather pipetting or vortexing and takes a long time - be patient.

  • Measure OD:

Measure the OD-600 of a 1:100 dilution of the cell suspension. (In the cuvette, mix 0.99 mL water and 0.01 mL cell suspension). Note: The desired concentration is 2.5*1011 cells per mL, giving 1*1010 cells per 40 μL. This corresponds to an OD-600 (after 100x dilution) of roughly 3.75. It is difficult to reach this value, but it is still important to know the concentration of cells to calculate efficiencies.

  • Dilute the cell suspension to a concentration of 2 x 10^10 to 3 x 10^10 cells/ml (1.0 OD600 = approx. 2.5 x 10^8 cells/ml) with ice-cold GYT medium.
  • Test for arcing:

Transfer 40 ul of the suspension to an ice-cold electroporation cuvette (0.1-0.2 cm gap, on middle shelf next to electroporator) and test whether arcing occurs when an electrical discharge is applied. Place the cuvette in the green holder attached to the machine. Go to option 4, Pre-set protocols; choose bacterial; choose the correct choice for your size cuvette, probably the first option for a .1 cm cuvette. If arcing occurs, wash the remainder of the cell suspension once more with ice-cold GYT medium to ensure that the conductivity of the bacterial suspension is sufficiently low (<5 mEq).

  • Storage:

Store cells at -80°C until they are required for use. For storage, dispense 40 ul aliquots of the cell suspension into sterile, ice-cold .5 ml microcentrifuge tubes, drop into a bath of liquid nitrogen (This rapid freezing is not strictly necessary but could be fun) and transfer to a -80°C freezer. To remove the tubes from the liquid nitrogen bath, bring out into the hall along with a storage box, and pour the tubes and liquid nitrogen into the box. Once all the tubes are out, close the box most of the way and let the liquid run out into the hallway. Try not to do this in the very center of the walkway!

To use frozen cells: Remove an appropriate number of aliquots of cells from the -80°C freezer. Thaw the tubes on ice.

Risk Assessment