Introduction

1. Why do we detect benzo[a]pyrene?

   Because when food, such as fried food , is heated above 300 degrees celcius, benzo[a]pyrene is released. That is why recycled oil usually contains benzo[a]pyrene [1].

2. The harm of benzo[a]pyrene

   Pathway: from skin, breathing in, and eating. It is carcinogenic and causes environmental pollution. It causes skin irritation and eye irritation [1].

3. Taiwanese regulation
   
4. National regulation
   • Europe:same to Taiwanese regulation[2]
   • American:The MCL has been set at 0.2 ppb[3]

Circuit Design

So far,we don’t find the protein which can combine with the Benzo[a]pyrene,so first we must degradate it by Laccase. And its product is Bap-1,6-quinone which can combine with the protein,in order that we can detect Benzo[a]pyrene.[4] We put the gene fragment which can produce the Laccase in the E.coli. Let it produce itself.

QsrR is a protein which can combine with Bap-1,6-quinone.[5]As Laccase,we put the gene fragment in the E.coli. Let it produce itself.

We design a gene part make QsrR repress sfRFP’s production. Usually,QsrR is on the Binding Site,and red fluorescent protein will not be produced. When QsrR combine with Bap-1,6-quinone, QsrR will be activated and go away. And the transcription will carry on,then it will produce red fluorescent protein.

Result

1. Whether benzo[a]pyrene can enter e.coli or not
   1. Method

   Detection of the amount of toxins in the e.coli.

   • (1)Add 100μl of DH5α and 900μl of LB broth into the tube and incubate for 1hr.
   • (2)Centrifuge at 4000rpm for 3min and clicard 800μl of the supernatant
   • (3)Plate each 100μl of the bacteria onto the dishes and spread.
   • (4)Incubate the plates at 37℃ overnight
   • (5)Prepare each concentration of the toxin.
   • (6)Statutory standards *100 / *10 / *1 / *0.1 / *0.01

   Next day

   • (1)Prepare 16 microcentrifuge tubes.(5 kinds of concentration *3 timings+control)

     (2)Add 500μl of DH5α to each tube.

     (3)Centrifuge all tubes at 4000rpm for 3min.

     (4)Remove the supernatent.

     (5)Add 1000μl of the toxic solution each time.

     (6)Follow the concentration and 3 timings(0.5hr / 1hr / 1.5hr).

     (7)Add 0.5cc of ddH₂O and mix with the bacterias

     (8)Centrifuge at 13000rpm for 30 sec

     (9)Remove the water

     (10)Repeat step1~step3 for three times

     (11)Add 1cc of ddH₂O and mix with the bacterias

     (12)Centrifuge at 13000rpm for 30sec.

     (13)Remove 700μl of the supernatant

   • Kill the bacteria:

     (1)Put all the tubes in the Liquid nitrogen

     (2)When they freeze,heat them at 100℃

     (3)Repeat step1~step2 for 3 times

2. Whether e.coli is alive in the poisons, condition or not
   1. Method

   DH5α-Pretest

   Procedure

   Because we must test E.coli’s Survival in the environment there is benzo[a]pryene by counting the colonies,First we test how much concentration is the best.

   1. culture

      STEP1:take 1μL DH5α to spread the plate(no Antibiotic)

      STEP2:put in 37 degree Celsius 12~16hr

   2. liquid culture

   3. STEP1:put 80μL into 2ml LB broth

      STEP2:recovering

      STEP3: After 2hr,dilute it to 10^-4,10^-5,10^-6,10^-7,and then go to spread the plate (no Antibiotic)

      STEP4: After 4hr dilute it to 10^-4, 10^-5 ,10^-6 ,10^-7 ,and then go to spread the plate (no Antibiotic), 6hr and 8hr Similarly

      STEP5:Take 200μL out from the tube and spread the plate(Ampicillin)

      STEP6: put in 37 degree Celsius 12~16hr

   Survival

   Procedure

   First we culture DH5α with LB only plate for 15hr. Then,pick one colony in the LB broth,and liquid culture for 15hr.

   We divided two categories A and B.

   A:

   Take 80μL into 2ml LB broth × 6 tubes and then culture 1 hr.

   After 1hr,add 20μL benzo[a]pryene into three tubes(conc. Is 2000ppb(A thousand times the standard value))

   And add 20μL DMSO into the other tubes.Then,culture for 3hr.

   After 3hr,dilute the broth to 10^-6

   And take 200μL to spread the plate.

   B:

   Take 80μL into 2ml LB broth in a tube And then culture 1 hr.

   After 1hr, put them into 6 tubes equally.

   Dilute the broth to 5×10^-4

   Add 0.4μL benzo[a]pryene(2×10^-4) in three tubes.

   Add 0.4μL DMSO in the other three tubes.

   Go to 37 degree Celsius shaking for 10min.

   Take 200μL to spread the plate.

   
   2. Results
      

      The number of the colonies in the Ampicillin plate is zero.

      According to the result, 2hr 10^-5 and 4hr 10^-6 is the best.

      

      2hr plate from left to right is 10^-4,10^-5,10^-6,10^-7

      

      4hr plate from left to right is 10^-4,10^-5,10^-6,10^-7

      

      Ampicillin Plate

      According to the result, Beno[a]pryene does not affect E.coli’s survival.

      But Category B is failed because its number of colony is too much.

      

      Benzo[a]pryene Category A

      

      Control Category A

      

      Benzo[a]pryene CategoryB

      

      Control CategoryB

Reference

• [1] Smoked foods Mechanism of benzo (a) pyrene and prevention methods
• [2] Reduce operating guidelines in food polycyclic aromatic hydrocarbon content of the (draft)
• [3] Basic Information about Benzo(a)pyrene in Drinking Water
• [4] Hadibarata T, Kristanti RA. Identification of metabolites from benzo[a]pyrene oxidation by ligninolytic enzymes of Polyporus sp. S133. J Environ Manage. 2012 11/30;111(0):115-9.(2013 IGEM CUHK)
• [5] Ji Q, Zhang L, Jones MB, Sun F, Deng X, Liang H, et al. Molecular mechanism of quinone signaling mediated through S-quinonization of a YodB family repressor QsrR. Proceedings of the National Academy of Sciences. 2013 March 26;110(13):5010-5. (2013 IGEM CUHK)