Team:Imperial College/mainresults

We used E. coli that expresses PhaCAB enzymes to make P3HB bioplastic. P3HB produced in cells were stained with Nile Red for fluorescent microscope imaging, and strong fluorescence was detected at the area where PhaCAB-expressing cells were streaked.

E.coli transformed with the phaCAB operon(native, hybrid and constitutive are different promoters expressing the operon) fluoresce when grown on LB-Agar plates with Nile Red stain. The P3HB produced within them is stained. Those without the operon do not(EV- transformed with empty pSB1C3). When the promoter is changed from the native form to the hybrid or constitutive J23104 then the fluorescence is more intense, indicating increased P3HB production.

In order to realistically improve our experimental design, we produced P3HB synthesis model with considerations of central metabolic pathway within the cells. Our model predicts that during the synthesis of P3HB, the concentration of PhaB enzymes is an important rate limiting factor that can actually be regulated.

PhaB concentration in the chassis is a rate limiting factor in P3HB synthesised. The parameter values are from various sources, thus the simulation result should be interpreted as a qualitative perspective and the trend should be observed.

Since our model predicts that P3HB production can be significantly improved by expressing more P3HB polymerase PhaB, we designed a hybrid promoter consists of the J23104 constitutive promoter and the native promoter to optimise gene expression. Our results show that we have successfully produced 11-fold more P3HB bioplastic compared with the native promoter.

Comparison of P3HB production . (left) 1.5ml tube, natural phaCAB (BBa_K934001) (right) 5ml tube, phaCAB expressed from the hybrid promoter, (BBa_K1149051).

A summary of the improved production of P3HB by our hybrid promoter-phaCAB construct(BBa_K1149051) over the native promoter-phaCAB.

One of the objectives of Module 1 is to produce P3HB bioplastic from waste. By comparing degradation product 3HB of P3HB bought from Sigma, produced from glucose and produced from the waste, we found there is no significant differences in 3HB concentration between these samples.

The chemical analysis of the produced bioplastic. The samples break break down to 3HB monomers after treatment with our PhaZ1 enzyme (BBa_K1149010). We synthesised P(3HB) using our improved Biobrick part (hybrid promoter phaCAB, BBa_K1149051). Our engineered bioplastic producing E.coli synthesised P(3HB) directly from waste. Imperial iGEM data

Degradation of P3HB produced from various sources showing no significant difference between P3HB made from waste and P3HB made from other sources.

Our clearing zone assay indicates that P3HB depolymerase PhaZ1 started to fairly quickly degrade P3HB from the first day. After 3 days, there is evidently a clear zone around the well containing PhaZ1. We are the first iGEM team to degrade bioplastics!

PhaZ1 showing P3HB degradation ability by generating a clear zone on a P3HB LB agar plate. A. No difference between empty vector cell lysate and PhaZ1 cell lysate right after they were pipetted into the wells. B. PhaZ1 in the cell lysate started to clear P3HB around the well after 1 day. C. PhaZ1 created a clear zone around the well after 3 days, whereas it was still cloudy around the empty vector cell lysate well.