Difference between revisions of "Team:Amsterdam/Design"

The first thing we wanted to demonstrate was co-culture growth in which an E. coli culture was able to grow on the carbon shared by Synechocystis. We innoculated 48-well plates with different starting ratios of Synechocystis and E. coli. We used both the lactate-producing Synechocystis strains whose genetic instability we showed earlier, as well as the acetate-producing strain based on the acs knock-out. Cells were counted using a coulter-counter before innoculation and re-counted every 24 hours for seven consecutive days. Results are shown in figure 1 for the acetate producer & E. coli consortium, while results for the lactate-producer & E. coli consortium are shown in figure 2. Overall, all consortia seem to converge to a common final ratio, showing robust population dynamics governed by the carbon-sharing dependency of E. coli on Synechocystis. This result is perfectly aligned with our in silico simulations {link} that had predicted the existence of attractor states, quite robust to fluctuations in model parameters such as the initial ratio of Synechocystis:E. coli.

Our first attempt to demonstate product-production in a synthetic consortium involved our stable acetate-producer and an isobutanol-producing E. coli strain. The latter was obtained via the isobutanol pathway biobrick that was part of this year’s distribution kit and submitted by Bielefeld’s iGEM team last year. Their isobutanol pathway consists of four enzymes under the control of an inducible promoter. Unfortunately, despite succesfully transforming an E. coli strain, we could not demonstrate subsequent isobutanol production in neither stand-alone E. coli growing on various carbon sources nor E. coli driven by Synechocystis stable supply of acetate.

Approach 2: Three-step meso-butanodiol production

In an ambitious last attempt to demonstrate product formation using a consortium, we combined an acetoin-producing E. coli strain available in our lab with a previously-engineered Synechocystis strain that produces glycerol via insertions of a gene coding for phospho-glycerol phosphatase (ggp), which catalyzes the dephosphorylation of glycerol-3-phosphate to glycerol (Savakis, 2015). We reasoned that with a modified glycerol-producing strain also created in our lab by Philipp Savakis, the separate compartments of Synechocystis and E. coli could be used to more favourably drive a reaction towards the production of meso-butanediol, an important chemical precursor for a variety of industrial chemicals and biofuels. Previous attempts involved producing meso-butanediol from acetoin within the same compartment in a single cell (figure 2). The flux to meso-butanediol, however, is hampered by the series of redox-reactions with overall unfavourable thermodynamics due to presence in the same compartment. To overcome this, we designed the following consortium:

After several days of turbidostat innoculation, we managed to show meso-butanediol production using HPLC. Although we obtained these results mere hours before the wiki-freeze and are as such far from being fully exploited, the result demonstrates the potential of using a consortium for successfully driving product-flux using compartmentalisation in what would otherwise be an unfavourable thermodynamic environment.