Team:Chalmers Gothenburg/Description
Introduction
Current chemical synthesis based on a petroleum based platform have led to a disruption of environmental systems and continue to be a strong contributor to the emission of greenhouse gases. The accumulation of greenhouse gases, most notably carbon dioxide, is already creating dramatic changes in the worldwide temperatures and climate [1]. In 2016, our planet has reached the warmest global temperature ever recorded [2]. Human activity has been shown to be the main impacting factor of the increase of greenhouse gas concentrations during the last 150 years [3]. It has been proposed that even if the carbon dioxide emission stops immediately it would take 1000 years for the concentrations to return to normal level [4].
Climate change is one the most important issue affecting our modern world, and we need to consider alternative ways of life to reduce our environmental impact. Several measures are being taken by scientists and industry to reduce the emission of greenhouse gas as much as possible, with carbon dioxide as the main focus. We have let this issue be an inspiration to us and came up with the main idea of our project. Inspired by nature, the idea is to utilize carbon dioxide as a carbon source for a system that could produce useful products while reusing excess carbon dioxide.
Our project aims to use the carbon fixing ability of a photosynthetic microorganism to produce a carbon source that can be utilized by a wide range of microorganisms that are already used in industry for the production of chemical products today. For our photosynthetic microorganism we chose the cyanobacteria Synechocystis. We chose Synechocystis over, for example, microalgae because as a cyanobacteria it generally grows faster and have more tools available for genetic engineering [5].
The basic design
Since the carbon source is a major part of the cost for running industrial biosynthesis, utilizing carbon dioxide could be a major advantage not only from environmental perspective but also from an economical point of view. In order to achieve a stable co-culture, a dependent relationship between the two organisms is desired. This can be achieved in several ways, for example through quorum sensing [6] or metabolite exchange [7]. An exchange of metabolites was chosen due to the advantages of such a system, for example by providing additional fitness benefits due to the division of metabolic labor [8]. It has also been shown to be capable of purging cheaters from the system, i.e. cheaters do not seem to be able to outcompete the cooperating population [7]. Furthermore, in 2015 the Amsterdam iGEM team achieved a proof of concept in which they created a symbiotic culture between the cyanobacterium Synechocystis and Escherichia coli based on auxotrophy. This provided us with great inspiration on how to achieve our production system.
The resulting system will allow for the direct conversion of atmospheric carbon dioxide into commercially used chemicals that are currently derived from fossil sources of carbon, as illustrated in Figure 1.
The chosen production organisms were Bacillus subtilis, Escherichia coli, Yarrowia lipolytica and Saccharomyces cerevisiae. They were chosen since they have all proven to be capable of industrial level production. Furthermore, all of them have been the subject of extensive research, providing a good foundation for continued development.
How will this work?
The modifications planned for each organism in the project are summarized in Figure 2. The project is divided into two systems: either with a prokaryotic or a eukaryotic production organism. For the prokaryotic organisms, arginine is overproduced and secreted. The cyanobacterium, which has its own gene coding for arginine biosynthesis knocked out, is therefore allowed to grow. The same strategy is used for the eukaryotic system, except glutamine is used instead of arginine. In both systems cyanobacteria will secrete acetate, acetate will be the only carbon source available for the production organisms thus leading to a co-dependency. This is achieved by overexpression and knock-out of several genes. For more details about the modifications, see the constructs page.
