That bacteria can make plastics, which can in turn be used for packaging films for example, it is not immediately obvious, but it is by now an established process and is used today to generate bioplastics which can be found in commercial products. However, the feedstock used for fermentation by bacteria has always been a pure carbon source, such as sugar or fatty acids, which can account for up to 50% of production costs for bioplastics. There would be large benefits in feeding the bacteria a steady diet of waste materials, so the latter would not need to be landfilled and instead could generate valuable new materials, with the potential for cutting costs as well, a win-win-win situation. Christopher Nomura and his lab at Syracuse University, in their article published in the Journal of Applied Polymer Science, review the progress in using waste products from another thriving industry, the biodiesel industry, to use as a starting point to make bioplastics1. Biodiesel production generates vast amounts of waste glycerol, roughly 400 thousand metric tons in the US alone in 2011 (about 10% of the final biodiesel weight eventually produced) 2. This glycerol cannot be cheaply used to make cosmetics and the likes, as it is not pure enough.
A number of bacteria can take glycerol from their surrounding environment and transform it into building blocks that they can use in turn to grow and develop. In some of these bacteria, when carbon sources are abundant and other nutrients like oxygen and nitrogen are not, polymers called polyhydroxyalkanoates, which eventually will be harvested to make bioplastics, are produced as energy reserves. Through metabolic genetic engineering, scientists can also improve the bioplastics yield of these bacteria, further refining the process and lowering costs. Nomura and co-workers show that a number of different bacterial strands produced in several labs around the world can generate bioplastics from waste glycerol with yields that are competitive with those obtained using pure carbon sources. This in turn means that the biodiesel industry can lower its costs by selling a valuable product instead of landfilling waste. In addition, the properties of these plastics can be tailored with an eye towards different applications’ requirements.
One of the biggest selling points of bioplastics is the fact that they are biodegradable, so for a variety of applications, such as medical implants that need to dissolve gradually inside the body, they have a built-in advantage over traditional plastics. Biodegradability also means they eventually dissolve as opposed to occupying space in landfills. Adding to these “green” credentials the ability to be generated largely from the waste output of another “green” industry further adds to the bioplastics’ environmental street cred.
1. C. J. Zhu, S. Chiu, J. P. Nakas, C. T. Nomura, Journal of Applied Polymer Science DOI: 10.1002/app.39157
2. C. J. Zhu, C. T. Nomura, J. A. Perrotta, A. J. Stipanovic, J. P. Nakas, Biotechnology Progress 26 424 (2010)