Bio-waste becomes plastic using "trained" bacteria

TU Delft doctoral candidate and researcher Jean-Paul Meijnen has shown that bacteria can be “trained” to break down plant waste into the chemicals that are the basis of bioplastics. The bacteria goes through a little gene therapy, a little evolutionary selection and finally training to achieve this feat.

Corn based plastics have been around for a while. You find this type of plastic in disposable dinnerware and drink bottles. Unfortunately, these plastics use the food portion of the corn making them a less desirable product because it diverts food out of the food stream.

Solegear has developed more durable plastics using various woods, hemp, bamboo and rice husks. Using these non-food plants is more acceptable for the reason stated above.

Meijnen’s plastic process uses food production waste like vegetables, fruit and garden waste also known as bio-waste. Bio-waste uses only the food and plants left over after food is prepared. He uses bacteria that breaks down the sugars in the waste into bioplastic. Although a variety of sugars are created from the pretreatment of the food waste, three different types of sugar – glucose, xylose and arabinose – comprise 80 percent of the total sugars.

Originally Meijnen used the bacteria, Pseudomonas putida S12, to break glucose down further into chemicals for bioplastic production. The bacteria would not break down xylose and arabinose leaving too much bio-waste behind. Until all three of the major sugars could be broken down, the process would not be economically viable.

"Unfortunately, the production of plastics from bio-wastes is still quite an expensive process, because the waste material is not fully utilized," explains Jean-Paul Meijnen. "A logical way of reducing the cost price of bioplastics is thus to ‘teach’ the bacteria to digest xylose and arabinose too."

In order to remedy the matter, Meijnen modified the bacteria and “trained” it to break down the other two sugars as well. He began by inserting specific DNA fragments in the bacteria to pretreat xylose for further processing by the Pseudomonas putida S12. Two genes from E.coli “which code for two enzymes” were introduced. Those enzymes enabled the conversion of xylose in a two stage process to molecules that Meijnen’s primary bacteria could break down into bioplastic. Still only 20 percent of the xylose was broken down.

Meijnen improved the xylose process by training the bacteria through an evolutionary process. The best performing bacteria were “successively selected”.

"After three months of this improvement process, the bacteria could quickly digest all the xylose present in the medium. And surprisingly enough, these trained bacteria could also digest arabinose, and were thus capable of dealing with the three principal sugars in bio-wastes." Meijnen also incorporated other genes, from the bacterium Caulobacter crescentus. This procedure also proved effective and efficient from the start.

He was also able to train his Pseudomonas putida S12 to produce para-hydroxybenzoate (pHB) from xylose, glucose, and glycerol. Parahydroxybenzoate is used as a preservative in the cosmetic and pharmaceutical industries.

"This strategy also proved successful, allowing us to make biochemical substances such as pHB from glucose, glycerol and xylose. In fact, the use of mixtures of glucose and xylose, or glycerol and xylose, gives better pHB production than the use of unmixed starting materials. This means that giving the bacteria pretreated bio-wastes as starting material stimulates them to make even more pHB."

Apparently training bacteria could lead to the production of a number of petroleum alternatives from bio-waste. Better yet, “No meals were harmed” in the making of these chemicals a very important aspect of the process.

Training bacteria to produce chemicals from bio-waste for bioplastics or preservatives is a wonderful way to transition away from petroleum and food based processes.

23.11.2010. 19:27

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