Washington: Researchers have been able to ‘train’ bacteria to convert all the main sugars in vegetable, fruit and garden waste efficiently into ‘green’ products like bioplastics.
By adapting the eating pattern of bacteria and subsequently training them, NWO and TU Delft Researcher Jean-Paul Meijnen succeeded in converting sugars in processable materials, so that no bio-waste is wasted.
Lignocellulose, the complex combination of lignin and cellulose present in the stalks and leaves of plants that gives them their rigidity, is such a material.
"Unfortunately, the production of plastics from bio-wastes is still quite an expensive process, because the waste material is not fully utilized," Meijnen said.
The pre-treatment of these bio-wastes leads to the production of various types of sugars such as glucose, xylose and arabinose. These three together make up about eighty per cent of the sugars in bio-waste.
The problem is that the bacteria Meijnen was working with can only digest glucose but not xylose or arabinose, thus leaving eighty per cent remains unused.
"A logical way of reducing the cost price of bioplastics is thus to ``teach`` the bacteria to digest xylose and arabinose too," he said.
The bacteria are genetically modified by inserting specific DNA fragments in the cell; this enables them to produce enzymes that assist in the conversion of xylose into a molecule that the bacteria can deal with.
This method did work, but not very efficiently: only twenty per cent of the xylose present was digested. The modified bacteria were therefore ``trained`` to digest more xylose.
Finally, in a separate project Meijnen succeeded in modifying a strain of Pseudomonas putida S12 that had previously been modified to produce para-hydroxybenzoate (pHB).
He tested the ability of these bacteria to produce pHB, a biochemical substance, from xylose and from other sources such as glucose and glycerol.
"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."
The study will be presented at TU Delft on Monday 22 November 2010.