Environmentally vs. Economically friendly plastics
In order to be cost efficient, it is crucial to produce polymers using methods that will yield high productivity as well as lower cost. Amongst the many biodegradable polymers, PHB, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) and poly (3-hydroxyhexanoate-co-3-hydroxyoctanoate) are the ones that have been produced with high productivity [6]. In order to reduce the production cost, a gene transfer from A. eutrhopus to the plant Arabidopsis thaliana (Figure 5) can be done through genetic engineering.
Figure 5. PHB granules in the chloroplasts of A. thaliana (Lenz & Marchessault, 2004)
Since A. eutrhopus belongs to the kingdom of prokaryotes, its DNA is not enclosed by a nucleus, and therefore its genetic information, as a single stranded plasmid, can be transferred to other organisms [7]. The three genes of A. eutrhopus, which are responsible for the expression of enzymes involving in the manufacturing of polymer, can be inserted into the DNA of A. thaliana through a technique called gene-splicing. Plastic polymers were found in the cytoplasm, nucleus, and vacuole of the plant and harvested through multiple-step chloroform extractions to separate the polymer from plant materials. Extracting polymer directly from A. eutrhopus could cost $4 per pound while harvesting this plastic from A. thaliana would only cost about $1.50 per pound. However, although it is less costly to produce polymer by transgenic plant, A. thaliana only yields polymer equal to about 14% of its dry weight. More studies on how to improve productivity is needed in order for it to be economically significant to the biodegradable polymer production [6]. However, neither the A. eutrhopus nor the A. thaliana means of harvesting polymer costs nearly as little as “normal” petroleum-based plastic production, which only costs about 50 cents per pound [7]. Per year, approximately 600 tons of biodegradable plastic are produced while one factory produces 100,000 tons on average of non-biodegradable plastic.
Potatoes are also another candidate for genetic engineering with the goal being to replace starch production with polymer production. Another group of plant polymer-producer candidates are oilseed crops. Yet further studies on how to develop polymer synthesis in plants are definitely needed [8].