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 [1]. 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 [2].

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 can futher be used as carbon materials 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) [3]. 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 [3]. 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 [4].