Team:CSU CHINA/Poster

Poster: CSU_CHINA


Clean the contamination of Cadmium

Hao Zhou, Chen Ziwen, Mingyu Liang, Yanzhe Zhang, Haonan Zhou, Haoran Hu, Jialong Ruan,Tianyuan Xie, Zhang Gengxin, Dongni Hong, Junxi Liao, Wang Xianghe, Yao Xiao, Xiangyu Chen, Yaxian You, Yuyang Peng, Runyu Lyu, Jiayi Pan, Siqi chen, Jiayu Chen, Zhaoxi Wu, Shiyu Lin, Li Tao, Linhu Xiao, Kelvin Zheng Li, Wen Wen, Lina Ma, Enyou Si, Xiangyu Li, Yufan Dong, Bin Zhang, Danyang Wang, Xutong Guo, Jufang Huang, Shanni Li, Jiada Li, Jie Li, Chiyu Li

School of Life Sciences, Central South University, Changsha, Hunan, China

Abstract

Recently, the cadmium-contaminated rice circulating in the market. Long-term intake of cadmium will jeopardize human bodies. To deal with the problem, we utilize engineered Synechocystis as a competent cadmium absorber. Moreover, with blue-ray/antitoxin suicide system, the reformed alga will be appropriately contained. The cadmium can be recycled as the microorganisms will be calcined after absorption. The application of engineered alga will minimize human potential cadmium intake.

Goal

1. To reduce the cadmium content in the water by using the modified Synechocystis.


2. To increase cadmium tolerance of Synechocystis in a high cadmium concentration environment.


3. To avoid environmental pollution caused by the escape of Synechocystis.

Inspiration

Cadmium contamination of water worldwide is already having a severe environmental impact, especially on crops, such as cadmium rice. In addition, cadmium contamination is likely to cause itai-itai disease and renal tubular injury, after prolonged and/or high exposure may eventually to renal failure, thus, the problem of cadmium pollution of water needs to be solved urgently. We adopt an environmentally friendly biological approach——use Synechocystis sp. PCC6803 with a clear genetic background and a certain degree of tolerance to cadmium as a chassis organism for transformation.


First of all, we translate cadmium, which is enriched on the cell wall through transporter proteins. However, this may cause photosynthesis failure, protein inactivation or oxidative stress in Synechocystis and lead to cell death, making it difficult to achieve high tolerance rate. Therefore, after transporting large amounts of cadmium ions into the cells, we accumulate heavy metal ions and prevent them from being transported out of the cells by chelating proteins. At the same time, we increase the expression of oxidoreductase to remove reactive oxygen clusters in the cells, thus increasing the growth rate of algae under cadmium ion stress. Besides, for high expression of functional proteins, We optimized the codon preferences of the algae, and analyzed the protein expression results.(Figure 1)


Figure1: The core “transport-chelation-redox reaction” system of our project
Problem
What is the problem your team is working to solve? How does it affect the world?
Cyanobacteria accumulates Cadmium

We use Synechocystis, a kind of Cyanobacteria, as the chassis organism to carry out genetic engineering modification and fix it in the calcium-alginate microbeads(Ca-Alg MBs) to immobilized bacteria.


We used the “Transport-Chelate-Redox” System to increase cadmium uptake and cadmium tolerance of Synechocystis, and designed a “Light-Regulated Toxin-Antitoxin” Suicide System to ensure the death of spillover engineering Cyanobacteria and avoid biological pollution.


Besides, using calcium alginate embedding immobilized method to Synechocystis in Ca-Alg MBs can not only immobilize our biological chassis, but also improve the cadmium elimination.

Engineering
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Section 1
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transportation - chelate - redox

Cadmium contamination of water worldwide is already having a severe environmental impact, especially on crops, such as cadmium rice. In addition, cadmium contamination is likely to cause itai-itai disease and renal tubular injury, after prolonged and/or high exposure may eventually to renal failure, thus, the problem of cadmium pollution of water needs to be solved urgently. We adopt an environmentally friendly biological approach——use Synechocystis sp. PCC6803 with a clear genetic background and a certain degree of tolerance to cadmium as a chassis organism for transformation.


First of all, we translate cadmium, which is enriched on the cell wall through transporter proteins. However, this may cause photosynthesis failure, protein inactivation or oxidative stress in Synechocystis and lead to cell death, making it difficult to achieve high tolerance rate. Therefore, after transporting large amounts of cadmium ions into the cells, we accumulate heavy metal ions and prevent them from being transported out of the cells by chelating proteins. At the same time, we increase the expression of oxidoreductase to remove reactive oxygen clusters in the cells, thus increasing the growth rate of algae under cadmium ion stress. Besides, for high expression of functional proteins, We optimized the codon preferences of the algae, and analyzed the protein expression results.(Figure 1)


Figure1: The core “transport-chelation-redox reaction” system of our project
Section 3
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Results
What did your team achieve? What do you plan to work on moving forward?
References and Acknowledgements

We extended module level from cell into the real world through this model. Based on We extended module level from cell into the real world through this model. Based on element analysis, we rebuilt the microbead and cells virtually, and predict its reaction, then get the module optimized.


Model 1: \( {Cd}^{2+} \) flow between environment and microbead

Model 2: \( {Cd}^{2+} \) flow between algae and microbead

Model3: Predict absorption saturation time & Optimization

Model4: Predict rupture time & Optimization


raw cell concentration 108cell/cm3 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
rupture time /h 90 63 49 38 31 26 23 22
Poster Title
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Section 1
Use this section to explain whatever you would like! Suggestions: Safety, Human Practices, Measurement, etc.
"Toxin-antitoxin" light-controlled suicide system

The escape of engineered synechocystis is one of the major hazards of genetically modified organism, which may lead to different adverse effects such as water bloom and reduction of water polymorphism. Considering these risks, we designed a blue-light-controlled "toxin-antitoxin" suicide system. (Figure 2) In this system we use the RelE/RelB-toxin/antitoxin system and regulate the expression of the toxin RelE through the blue light-regulated promoter. In the presence of blue light, the regularly expressed HTH-LOV-REP blue-regulated protein will homodimerize and specifically recognize the (c120)5 sequence upstream of the blue-regulated promoter via HTH, while inhibiting the expression of toxin RelE via the REP domain. When synechocystis escaped from the blue light environment we have set up, the uninhibited blue light regulatory promoter will initiate the expression of RelE and under the effect of our amplification system, the content of RelE will increase rapidly, as a result the escaped algae will be killed. Meanwhile in order to prevent the small amount of RelE that is still expressed in the presence of blue light from harming the algae, we regularly express the antitoxin RelB to neutralize its toxin to ensure that the toxin RelE does not harm the unescaped Synechocystis sp.PCC6803.


Figure 2:Third-generation system the Blue light regulated suicide system

Section 3

The model proves workability of the module with specific parameters, avoiding much wet exp work in the rough pandemic times. Our light-controlled suicide system is proven through this model to maintain the sustainability of regular cells and erase detached cells as expected.


System Off System On
Future

We designed a fly-catcher-like device, a blue light source is placed at the bottom of the center to deactivate safety system in cells. Algae in microbead create oxygen continuously and gas fuse into a bubble or two inside that provide buoyancy, the microbeads could float as the bubbles grow.


Meanwhile, the absorption process is still in progress. One of the main goals of our model is to optimize parameters to match the saturation time and float up time to maximize its efficiency. Once the absorption process is done, we expect the microbeads float on the surface. Once a microbead floats on the surface, it can just float for a while and rupture, then fall into groove on the top of the device waiting for salvage. Hence, the process of absorption and salvage is separated on time and space scales.




Due to COVID-19, the real implementation of the device just stayed at our to-do list. If possible, future CSU China team could continue to develop the project in 2021. We plan to install microelectronics in the device, including LTE and GPS modules and photoresistors, so that the device can sense the current light intensity and access future light intensity information from the local meteorological department by LTE. With the data sent to an app installed on the user's phone, algorithm based on our model inside the app will provide the user with the best salvage time.

References and Acknowledgements
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Poster Title
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