Team:Tokyo Tech/Toxin Assay/Overview
3-1-0. Overview
Contents
3-1-0. TA system
TA systems have function of controlling cell growth and are present on the genomic DNA of many microorganisms as well as on plasmid DNAs. We thought that exploiting the ability of TA systems was the best way to trace the story of Snow White, because the story includes death and recovery from death.
Preceding iGEM teams have studied the following TA systems: ccdB-ccdA (iGEM 2014 team ULB-Brussels and iGEM 2013 team UGent), Kid-Kis, Zeta-Epsilon(iGEM 2014 team Wageningen UR) and Hok-Soc(iGEM 2015 team UMaryland). The iGEM 2016 team Tokyo_Tech studied the mazEF system, which is one of the most vitally studied TA systems.
MazF (Toxin) specifically recognizes and degrades ACA sequences of mRNAs, thereby inhibiting translation and cell growth. MazE (Antitoxin for MazF) forms a MazF-MazE heterohexamer and neutralize the toxicity of MazF. If this system is used appropriately, it is possible to manipulate growth of E. coli cells as we expect, and wide range of biotechnological application is possible.
Fig. 3-1-0-1. Table. Achievement of TA System in the preceding iGEM
3-1-1. Adjustment of MazF expression
MazF has very strong ability to inhibit cell growth, it has been reported not restored even to express too expressed antitoxin2). Therefore, to clarify the expression of MazF capable of suppressing growth of E. coli, we examined optimal inducer concentration, downstream from the PBAD.
Fig. 3-1-0-2.
From the result of the experiment 1.1., when the assay of TA system using genetic circuit above, the optimal arabinose concentration was found to be 0.02%. However, when Arabinose concentration of 0.2%, GFP fluorescence intensity falls markedly.
3-1-2. mazEF System Assay
3-1-2-1. Stop & Go
Concentration of arabinose to express the appropriate amount of MazF was confirmed in the previous experiment. Based on the result, we have conducted an experiment whether it is control of growth by using the mazEF system.
We named this experiment as "Stop & Go" because it was to resume growth from suppression the cell growth.
Fig. 3-1-0-3.
From the results of the experiment 1.2.1., MazE was induced 2 h after MazE expression, and about 8 h later, cell growth that had stopped was recovered .
Although the revival took longer than expected, suggesting the strength of MazF as the toxin from this result.
3-1-2-2. Go & Stop
In Experiment 1.2.1, it has been found that growth is inhibited by toxin and resuscitated by antitoxin.
However, if to express the toxin after expression of antitoxin, we wonder how to behave is growth?
So if MazF expressed after MazE constitutively expressed, we studied how to grow.
From the results of the Exp.1.2.2, it was found that the larger expression of MazE is, the larger the number of E. coli is in the Stationary Phase.
Further, it was found that there is a correlation efficiency of translation and expression of MazE.
3-1-3. Control of Cell Growth
In order to further secure the control of cell growth, we conducted assay of TA system on the LB agar plate containing inducer of toxin or antitoxin.
This experiment was named “TA system ~Queen’s capricious～”, because it seemed that princess control a sleep for snow white,
From the results of the Experiment 1.3., it has been found that A cultured in a medium containing inducer of toxin initially may be able to control the colonization by the presence or absence of IPTG(inducer of antitoxin).
But E. coli cultured in a medium containing inducer of antitoxin initially were unable to control the colonization.
This result might indicate that function of toxin is not only growth inhibition
If all the above mentioned results are mobilized, it may become possible to freely control of the growth, make of the story with E. coli, product the material production in any timing.
3-1-4. Reference
1) Yonglong Zhang, Junjie Zhang, Klaus P. Hoeflich, Mitsuhiko Ikura, Guoliang Qing, and Masayori Inouye, MazF Cleaves Cellular mRNAs Specifically at ACA to Block Protein Synthesis in Escherichia coli. Molecular Cell, Vol. 12, 913–923.
2) Hazan, R., B. Sat, and H. Engelberg-Kulka. Escherichia coli mazEFmediated cell death is triggered by various stressful conditions. J. Bacteriol.186:3663–3669.
