October 26, 2011 | 3
Bacteria are capable of producing a wide range of exciting and important materials, and one of the most unusual is probably bacterial plastics. Used by the bacteria as an energy store, these bioplastics are of particular interest as not only could they be a non-oil-based form of plastic but they are also biodegradable. At the moment, they are still far more expensive than conventional plastics, but researchers are working on finding ways to make bacterial bioplastic a more viable alternative to synthetic plastics.
Commercial plastics are formed from long repeating carbon-based chains formed from simple chemical units. The plastic polyethylene for example is formed of many repeating ethylene units:
These long chain polymers are usually derived from oil, because oil contains a large number of long hydrocarbons. However long carbon molecules are also good for energy storage, and are usually seen in nature in the form of starch or cellulose. Some bacteria, rather than using starch, instead use a long-chain carbon storage molecule that is very similar to plastic. These are stored inside the bacteria as small granules, surrounded by the enzymes that create them.
While bacteria are great at making exciting molecules they are not always the best candidates for industrial scale production. Bacterial bioplastics are a good idea but for large-scale production the genes that produce these plastics would have to be moved into either more industrial strains of bacteria, yeast, or algae. Algae are an interesting choice, because not only do they have to capacity to produce a large amount of the plastic product, they also live off sunlight, and can be produced and harvested in large quantities. As oil is currently far cheaper than any natural plastics alternative, any move to decrease the price of bioplastics would increase it’s attractiveness for both the public and research investors.
Reference 1, below, details experimental work to do just that; transfer the genes that bacteria use for making plastic into an algae host. Large scale gene-moving doesn’t always work, but in this case the algae managed to produce plastics in up to 10% of the algal dry weight after only ten days. Not only could these plastics be extracted successfully, they could also be seen forming as granules within the algae, which must have been incredibly exciting for the researchers to watch!
The best thing about this experiment is that this represents what I would see as quite a rough transfer of DNA. The genes were moved over wholescale, in their original bacterial form. I suspect an increase in product could be obtained by adapting the DNA for the algae. While DNA is a universal molecule, different organisms prefer slightly different code, so optimisation of the DNA, and even adjustment of the flux of upstream precursor pathways, could go a long way to increasing the yield of bioplastic in algae.
Picture credit: Image courtesy of Alessandra de Martino and Chris Bowler, Stazione Zoologica and Ecole Normale Supérieure.
Ref 1 =Hempel F, Bozarth AS, Lindenkamp N, Klingl A, Zauner S, Linne U, Steinbuchel A, & Maier UG (2011). Microalgae as bioreactors for bioplastic production. Microbial cell factories, 10 (1) PMID: 22004563
Ref 2 = Rehm BH (2003). Polyester synthases: natural catalysts for plastics. The Biochemical journal, 376 (Pt 1), 15-33 PMID: 12954080