Designing organisms to process waste
The EU generates more than 600 million tonnes of plant-based waste every year, containing valuable compounds that could be used to produce chemicals which are currently derived from oil. EU-funded researchers have now designed a safe soil bacterium that could convert waste into useful products in a single step.
© Pixavril #66301151, source: stock.adobe.com 2019
Millions of tonnes of plant-based waste are produced by the EU every year. Lignocellulose plant matter that exists in the cell walls of woody plants is the most abundant organic matter on earth, yet it is currently not processed efficiently, meaning manufacturers instead use oil to produce chemicals that could be derived from lignocellulose.
Now research coordinated by the EU-funded FUTURE project has paved the way for waste to replace oil in certain areas of manufacturing.
Our project could lead to new types of biodegradable plastics being created from sugars from waste plant biomass, says principal investigator Pavel Dvořák of Centro Nacional de Biotecnología for the coordinating institute, Agencia Estatal Consejo Superior de Investigaciones Científicas in Spain. This could reduce the need for oil, which is currently used to create plastic cups, plates, bags or higher-value plastics used in medical applications.
Digesting the waste
One problem of lignocellulose waste, besides the fact it is difficult to biodegrade, is that it consists of a diverse mixture of sugars and chemicals, some of which can be quite toxic for micro-organisms, making it hard to find a way to artificially break down the lignocellulose. For this reason, researchers used genetic engineering to adapt an organism called Pseudomonas putida so that it could digest this kind of waste more effectively.
We modified the metabolism of Pseudomonas putida so it could eat several sugars together rather than one by one, explains Dvořák. The second major outcome was that we were able to display synthetic protein scaffolds on the surface of this bacterium; these could be used to attach enzymes for the degradation of polymers.
An advantage of Pseudomonas putida is that it is relatively resistant to toxic chemicals, unlike other micro-organisms used in industry. The problem is that these bacteria do not normally like to eat the various types of sugars that exist in lignocellulose waste at the same time they usually consume only glucose or mannose but do not eat other types of abundant sugar such as xylose. The FUTURE project adapted Pseudomonas putida so that it simultaneously eats three types of sugars that originate in lignocellulose.
Researchers also found a way to place an artificial scaffold on the surface of the organism. This can be used as an anchor for enzymes that are able to break down larger molecules so that the Pseudomonas putida is able to digest them. As far as we know, this is the first time that someone has succeeded in attaching this type of synthetic scaffolding to the surface of Gram-negative bacterium, says Dvořák.
The work has led to the publication of a paper this year in Metabolic Engineering, and one last year in Biotechnology Advances, as well as a patent application.
Ultimately, the research could lead to innovative new ways of processing waste paper, cardboard, forestry waste, agricultural waste and food waste, while eliminating certain demands for oil. We are continuing to engineer both the inside and the outside of the bacterium. A focus of our work going forward will be the development of new biotechnologies for conversion of waste plant biomass into bioplastics. And, in the future, other products which can also be used as pharmaceuticals, fragrances or agrichemicals, concludes Dvořák.
FUTURE received funding from the EUs Marie Skłodowska-Curie Actions programme.