Our last year’s iGEM experience strongly influenced the choice of our topic for the project this year. Previously, we visited the chromium producing companies in one of the industrial cities of Kazakhstan, Aktobe, and we observed the extent of the problem of industrial wastes in Kazakhstan. Interaction with the local population of affected cities informed our team about the negative consequences for people’s health, living conditions and environment. Fruitful ongoing collaboration with ERG Company on the hexavalent chromium elimination allowed us to see that our endeavours in the lab can make a change in people’s life. This inspired us to pursue the similar path of work related to bioremediation of industrial wastes using photosynthetic organisms. Thus, we have engaged in the project of bioremediation of hydrogen sulfide wastes from oil refineries using the cyanobacteria Synechococcus elongatus. The choice of the model organism is based on the undemanding autotrophic mode of energy harvesting and minimal nutrition supply, which ensure the growth of cyanobacteria in a variety of environments. Being easy to maintain and grow, we believe that waste eliminating cyanobacteria is a promising tool for decreasing the amount of wastes from the oil refining manufactures in our country. It will help not only to transform polluting industrial activity into safer and more ecological process but also produce useful materials.
What is the problem?
Many countries in the world are rich in natural resources and are successful in energy production. However, toxic substances released during industrial processes substantially harm the environment and the ecosystem in general. Kazakhstan is not an exception, taking into account its abundant oil resources, which represent 1.8% of global oil reserves . According to the Committee of Statistics of the Republic of Kazakhstan, almost 100% of the total generated waste is hazardous, while waste releases from mining and quarrying represent 16% of them .
There are two types of oil depending on the sulfur content - sweet and sour. 0.5% is the threshold value of sulfur content by mass above which oil is identified as sour. Sour oil is toxic, corrosive and needs to be processed to become valuable in the market. The problem of sour oil wastes is relevant not only to Kazakhstan but also to other countries that specialize in oil production. Although there currently are a few ways to refine oil wastes, most of them are economically unfriendly, selective or not efficient.
What are the expectations?
Our team wants to create a more convenient and cost-effective solution to the current problem of hydrogen sulfide by applying synthetic biology. Engineered cyanobacteria are expected to neutralize hydrogen sulfide present in the oil wastewater. Sulfur-doped carbon dots can further be used as nanomaterials for fuel cells to replace the platinum electrode in the oxygen reduction reaction.
What is the project based on?
The central biochemical process behind our project is photosynthesis. Certain microorganisms are flexible in switching from oxygenic photosynthesis (OP) to anoxygenic photosynthesis (AP) . In our project, we genetically modify cyanobacteria (Synechococcus elongatus PCC 7942) to switch to AP, which does not produce oxygen, as its name implies, and therefore utilizes other electron donors, like hydrogen sulfide.
How does it function?
An enzyme termed SQR (sulfide quinone reductase) catalyzes the initial step of AP, the oxidation of hydrogen sulfide. The reaction is coupled with the reduction of plastoquinone (PQ), which brings electrons to the Photosystem I (PSI). One of the main characteristics of AP is the Photosystem II (PSII) inhibition. The inhibition is regulated by the subunits of the PSII itself, in particular, D1 protein, which supports water oxidizing cluster of PSII. Thus, PSII gets inhibited and PSI accepts the electrons supplied by hydrogen sulfide . Overall, the cell performs photosynthesis and simultaneously clears up the wastewater from hydrogen sulfide.
Some safety measures
The safety system, that ensures control over transformed cyanobacteria, is chromophore-assisted light inactivation SuperNova protein. The photosensitizer protein SuperNova generates Reactive Oxygen Species under regular UV light. Phototoxic sensitivity range of the protein is 500-600 nm, which will allow it to eliminate transformed species to protect the environment from genetically modified organisms. The protein is a monomeric form of dimeric photosensitizer protein KillerRed, which is bound to the thylakoid membrane. Its monomeric structure ensures better localization in a fusion with the target protein, which makes it more convenient to use .
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