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Latest revision as of 21:10, 21 October 2021

Team:XJTU-China/model-population-dynamics

Modelling

The model of genetic circuits

Background

Based on the model of toggle switch, we designed a genetic circuits as the figure below shows.

The promoter λ P R controls the production of lacI, aroG, trpB and trpA, which catalyse the synthesis of tryptophan. The promoter P l a c controls the production of cl857 and pykA, which promote the growth of E. coli.

Theory

For x , let [ d x ] , [ r x ] and [ p x ] be the concentration of corresponding DNA, RNA and protein. And let [ I P T G ] be the concentration of IPTG.

For the transcription of promoter λ P R , we have

(3.1) { d [ r l a c I ] d t = k s y n , l a c I α λ P R , 0 [ d l a c I ] + k s y n , l a c I α λ P R 1 [ p c I 857 ] [ d l a c I ] k d e , l a c I [ r l a c I ] , d [ r a r o G ] d t = k s y n , a r o G α λ P R , 0 [ d a r o G ] + k s y n , a r o G α λ P R 1 [ p c I 857 ] [ d a r o G ] k d e , a r o G [ r a r o G ] , d [ r t r p B ] d t = k s y n , t r p B α λ P R , 0 [ d t r p B ] + k s y n , t r p B α λ P R 1 [ p c I 857 ] [ d t r p B ] k d e , t r p B [ r t r p B ] , d [ r t r p A ] d t = k s y n , t r p A α λ P R , 0 [ d t r p A ] + k s y n , t r p A α λ P R 1 [ p c I 857 ] [ d t r p A ] k d e , t r p A [ r t r p A ] .

where k s y n , x and k d e , x are the synthesis rate and the degradation rate of x respectively, α λ P R , 0 is the background expression rate of λ P R , and α λ P R is the induced expression rate of λ P R .

For the transcription of promoter P l a c , we have

(3.2) { d [ r c I 857 ] d t = k s y n , c I 857 α P l a c , 0 [ d c I 857 ] + k s y n , c I 857 α P l a c [ I P T G ] [ I P T G ] + [ p l a c I ] [ d c I 857 ] k d e , c I 857 [ r c I 857 ] , d [ r p y k A ] d t = k s y n , p y k A α P l a c , 0 [ d p y k A ] + k s y n , p y k A α P l a c [ I P T G ] [ I P T G ] + [ p l a c I ] [ d p y k A ] k d e , p y k A [ r p y k A ] .

where α P l a c , 0 is the background expression rate of P l a c , and α P l a c is the induced expression rate of P l a c .

For the translation of protein translation, we have

(3.3) { d [ p l a c I ] d t = k p s y n , l a c I [ r l a c I ] k p d e , l a c I [ p l a c I ] , d [ p a r o G ] d t = k p s y n , a r o G [ r a r o G ] k p d e , a r o G [ p a r o G ] , d [ p t r p B ] d t = k p s y n , t r p B [ r t r p B ] k p d e , t r p B [ p t r p B ] , d [ p t r p A ] d t = k p s y n , t r p A [ r t r p A ] k p d e , t r p A [ p t r p A ] , d [ p c l 857 ] d t = k p s y n , c l 857 [ r c l 857 ] k p d e , c l 857 [ p c l 857 ] , d [ p p y k A ] d t = k p s y n , p y k A [ r p y k A ] k p d e , p y k A [ p p y k A ] .

where k p s y n , x and k p d e , x are the synthesis rate and the degradation rate of the protein of x respectively.

Parameter

The parameters are shown in the table below.

PARAMETER VALUE REFERENCE
k s y n , x 0.019 s 1 https://2018.igem.org/Team:NUS_Singapore-A/Model
k d e , x 0.0013 s 1 https://2018.igem.org/Team:NUS_Singapore-A/Model
k p s y n , x 0.47 s 1 https://2018.igem.org/Team:NUS_Singapore-A/Model
k p d e , x 0.136 s 1 https://2018.igem.org/Team:NUS_Singapore-A/Model

Meanwhile, the correction is performed according to the CDS length.

NAME LENGTH CORRECTION RATE
RFP (Benchmark) 678 bp 1
lacI 1083 bp 0.626
aroG 1053 bp 0.644
trpB 1194 bp 0.568
trpA 807 bp 0.84
cl857 714 bp 0.95
pykA 1443 bp 0.47

Result

When t = 1000 min , add IPTG. When t = 2000 min , remove IPTG and raise temperature. The results are shown in the figure below.

Conclusion

From the figure, we can see that there are three stable states.

  • lacI, aroG, trpA and trpB (promoted by λ P R ) has the same trend of GFP in the model of toggle switch;
  • cl857 and pykA (promoted by P l a c ) has the same trend of RFP in the model of toggle switch.

Reference

XIAN YIN, HYUN-DONG SHIN, et al. 2017. P gas, a Low-pH-Induced Promoter, as a Tool for Dynamic Control of Gene Expression for Metabolic Engineering of Aspergillus niger. Appl Environ Microbiol. [J/OL], 2;83(6):e03222-16.


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