Impact of the monocultures on the environment
To provide clarity, some important impacts than the monocultures have on environment are listed her after:
- Soil erosion due to irrigation, wind and harvest: Where irrigation application is inefficient or rainfall is high, water withdrawal is generally coupled with the loss of valuable soil from the farm.
- Soil salinization and acidification: Salinization of soils typically results from over irrigation or inadequate drainage. Acidification is largely due to the use of inorganic nitrogenous fertilizers such as urea and ammonium sulfate. Under high rainfall conditions nitrate leaching occurs, which also promotes acidification.
- Water use: Sugar cane ranks among a group of crops noted for their significant water consumption (along with rice and cotton). High water withdrawal is generally coupled with the run-off of polluted irrigation water containing sediment, pesticides and nutrients.
- Use of chemicals: Herbicide used in sugar beet culture is among the highest compared to other crops. Inorganic fertilizers typically supply nitrogen, phosphorus and/or potassium in mineral form. Environmental impacts generally arise because the nutrients in the fertilizers are not entirely taken up by the crop but move into the environment. The overuse of fertilizers on cane or beet crops is typical of farming in general.
- Discharge of mill effluents: In some countries with weak environmental laws, a tremendous amount of matter is released straight into streams. Cane mill effluents tend to include heavy metals, oil, grease and cleaning agents.
A sugar factory that mills 1,250 tonnes of sugarcane daily uses 151,000 liters of water per hour and releases 30,000 to 75,000 liters of liquid, solid and gaseous waste.
Production of sugar in marine environments by our green microalgae, Chlamydomonas reinhardtii
Why an algae?
As it is a photoautotrophic organism, Chlamydomonas reinhardtii has the ability to fix carbon through carbon dioxide uptake and a source of light. Its metabolism can also be autotrophic, heterotrophic or mixotrophic. All of these characteristics explains why it is an interesting chassis in comparison to other classical model (bacteria or yeast) which always need an input of energy such as glucose. This microalgue is well-known as a model organism in the research field of photosynthesis and its genome has been characterized. Moreover, growing range of tools in molecular biology has been developed for use in Chlamydomonas, for example a brand new modular cloning tool was created and published in 2018, the MoClo toolkit set by Pierre Crozet et al. This tool offers a new field of possibilities for the use of Chlamydomonas as it is a very interesting microorganisms, whose biosynthesis and metabolic pathways can be exploited in synthetic biology. Indeed it was established that this microalgae could be used in the future to produce high values compounds for biotechnology industries.
How to make this algae survive in marine environment?
Furthermore, to make use of marine environment to produce sugar, we needed to have a microalgae that can survive in salty water. Then, we contacted Josianne Lachapelle who worked with Chlamydomonas reinhardtii and adapted some strains to live in high salt concentration medium. And she kindly accepted to provide us with some of these strains that we could use them to make sugar without competing with arable land.
What relevant sugar to produce in this algae?
The sugar we choose to produce in this microalgae is the trehalose C12H22O11. It is a disaccharide of glucose, that can be metabolized by Escherichia coli and Saccharomyces cerevisiae. Whereas, it is also present in Chlamydomonas it is mainly involved in stress response to H202 as an antioxydant and not as a source of energy. Without a self-production consumption, Chlamydomonas and trehalose are becoming an interesting combination for energy production. As a result, this energy source would potentially be fully extracted and used by chassis such as E. coli or S. cerevisiae for the production of molecules of interest by synthetic biology.
Our discussion with professionals and scientists who work with Chlamydomonas or other microalgae, on directed evolution or regulation played a major role in the further perspective of our project.
One of the main conclusion we got from our meetings was that algae did not bring an added value for the production of sugar or biofuels because of its high production costs. Indeed, the cost of the production will highly increase because of the energy to bring to the photobioreactor, the extraction and the collection of sugar.
Thus, the amount of sugar expected through the use of marine surfaces could be sufficient to meet the needs of synthetic biology development but would not enable a profitable production
Yield improvement
In order to improve the yield of the trehalose production, we thought about directed evolution. It aims to identify beneficial mutations on a gene or on a biosynthetic pathway. It is a major tool for synthetic biology in eukaryotes. This relies on in vitro generation of diversity. However, since C. reinhardtii can not replicate plasmids this tool would be limited in this microalgae. Also, C. reinhardtii has a significantly lower speed of replication than the classical chassis of SynBio (Escherichia coli, Saccharomyces cerevisiae). These particularities make the in vitro generation of a large-sized library of mutants by the classical "error-prone PCR" used in directed evolution, more complicated.
This is why we have been interested in the team BOKU-Vienna 2017 project . To make in vivo evolution in yeast and bacteria, they proposed another solution, a model of retrotransposon. As there is no tool to make directed evolution in Chlamydomonas yet, we worked on adapting this strategy to this organism.
Since directed evolution is an important part into the development of a powerful synthetic biology chassis, we met professionals to get expertise on the subject.
The main returns we had were that it was by itself an extensive and complex subject to work on and develop. Since the needs of such a chassis in the industrial environment for sustainable development were clearly exposed by the experts, it seemed more relevant to focus on our direct evolution tool instead of the sugar production itself.
GMOs, environment and legislation
Finally, an important part of our discussions focused on the legislation about GMOs in offshore platforms. The current legislation compels us to use a confined environment. Very interesting alternatives systems for the photobioreactor design such as biocontainment measures were brought out with all of the experts we met.
From the low added value of the genetically modified microalgae for the production of sugar, we knew how to use the compiled knowledge for a better valorization of our project though our retrotransposon. Indeed, meetings with professionals brought out the interest of our retrotransposon development for fundamental research and for production of various molecules of interest in biotechnology was clearly exposed.
In this case, the engineered microalgae would be an added value to improve the quality and quantity of molecules through a sustainable way of production at industrial scale. Therefore, it would not undergo the same regulations as GMOs used in offshore platforms
