Difference between revisions of "Team:Jilin China/Description"

All free-living bacteria carry the toxin–antitoxin (TA) systems controlling cell growth and death under stress conditions. Based on the nature and mode of action of antitoxins, TA systems have been classified into six different types[1-3]. The product of the toxin gene is a protein, while the product of the antitoxin is either a protein (in Type II, IV, V, and VI TA systems) or a non-coding RNA (in Type I and III TA systems). In Type IV TA system, the toxin protein and the antitoxin protein do not interact with each other and the antitoxin antagonizes toxin activity by stabilizing its targets[4].CbeA-CbtA is one of the Escherichia coli TA systems, and the toxin, CbtA, has been reported to inhibit the polymerization of bacterial cytoskeletal proteins, MreB and FtsZ[5].CbeA does not form a complex with CbtA but functions as an antagonist for CbtA toxicity[4].

CbtA inhibits the polymerization of bacterial cytoskeletal proteins, MreB and FtsZ. The fission of bacteria will be suppressed but the growth of bacteria is normal. CbeA was found to directly interact with MreB and FtsZ, and enhance the bundling of their filamentous polymers in vitro. Besides, CbeA can relieve the toxicity of CbtA. Unlike the mostly investigated type II TA system[6], toxin can directly kill bacteria rather than stagnating the growth of the bacteria.（Fig.1）

Figure 1. Type II and type IV TA systems.（A）The model for the type II TA systems. Toxin attacks its cellular target, this toxin activity leads to bacterial cell growth arrest and eventual cell death. Antitoxin can bind to toxin to form a complex and relieve toxicity.（B）The model for the type IV TA systems. Toxin inhibits the polymerization of MreB and FtsZ, this toxin activity leads to the fission of bacteria can be suppressed. Antitoxin promotes the formation of the higher-order structures of MreB and FtsZ filaments in vitro and relieve the toxicity of toxin.

Geneguard system is a system that can control the growth of the engineered bacteria and the expression of targeted proteins according to the environment of the bacteria. In terms of the feature of CbtA-CbeA, we designed our Geneguard system (Fig. 2). We used a low expression level promoter to express CbtA constitutively. When using an inducible promoter to express CbeA and other proteins of interest, we want to reach the aim that when no inducer exists, CbtA can only be constitutively expressed. Only when the inducer exists, bacteria can proliferate and express targeted protein.

Figure 2. Geneguard system

Since the Geneguard is a conceptive system, we cannot directly conduct the experiments to this system. After referring to other's work, we designed a characterization construct by which CbtA and CbeA can be induced by different inducer to detect their functions.

We designed Geneguard system and thought that it is of high value to apply. Biosafety is our best advantage in Geneguard system. We hope to solve the biosafety issues with our Geneguard system to reduce the risks of escape of engineered bacteria. For example, compared with traditional fermentation, one of the biggest problem of using engineered bacteria to ferment is biosafety. It is a real problem that we have to face when applying.

According to the results of our human practice and the ideas we got from the brainstorm, we designed a method of application. Read more in the next part.

[1] Page, R.; Peti, W. Toxin-antitoxin systems in bacterial growth arrest and persistence. Nat. Chem. Biol. 2016, 12, 208–214.
[2] Nathalie Goeders ， Laurence Van Melderen*（2014）Toxin-Antitoxin Systems as Multilevel Interaction SystemsToxins (Basel). 2014 Jan; 6(1): 304–324.
[3] Yamaguchi Y, Park J H, Inouye M. Toxin-antitoxin systems in bacteria and archaea[J]. Annual review of genetics, 2011, 45: 61-79.
[4] Masuda, H.; Tan, Q.; Awano, N.; Wu, K.; Inouye, M. YeeU enhances the bundling of cytoskeletal polymers of MreB and FtsZ, antagonizing the CbtA (YeeV) toxicity in Escherichia coli. Mol. Microbiol. 2012, 84, 979–989.
[5] Tan Q, Awano N, Inouye M. YeeV is an Escherichia coli toxin that inhibits cell division by targeting the cytoskeleton proteins, FtsZ and MreB[J]. Molecular microbiology, 2011, 79(1): 109-118.
[6] Yamaguchi Y, Inouye M. mRNA Interferases, Sequence‐Specific Endoribonucleases from the Toxin–Antitoxin Systems[J]. Progress in molecular biology and translational science, 2009, 85: 467-500.