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Cover story
Spinning straw into gold
Cover story
Spinning straw into gold
For biotechnologists, straw, wood waste or bagasse from sugar cane production are a source of raw materials: valuable substances can be extracted from them with the help of bacteria.
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Jülich researchers do not only have an eye on plastic waste as a source of raw materials. Another huge mass of unused resources is plant waste, which accounts for around 50 per cent of the world’s harvests. Microbiologist Prof. Jan Marienhagen and bioprocess engineer Dr.-Ing. Stephan Noack have joined forces for this purpose. Their aim is to obtain valuable biocomponents from plant waste, which is usually shredded and ploughed under or burned.
Picture above: For biotechnologists, straw, wood waste or bagasse from sugar cane production are a source of raw materials: valuable substances can be extracted from them with the help of bacteria.
They both want to understand the metabolism of bacteria in every detail and optimise it. On this basis, they then develop industrially relevant production processes. Ideally, this means putting the shaggy remains of pressed sugar cane, the bagasse, in as the input and getting valuable basic components for bioplastics, medicines, food or cement additives as the output. “Bagasse, straw or wood waste have the advantage that they are naturally degradable and do not require extra plants to be grown. So no additional cultivable land is swallowed up, and thus there is no competition with food production,” says Jan Marienhagen. “However, fungi and bacteria that metabolise the sugar components of these plant wastes and convert them into higher-quality products are often unsuitable for use in the laboratory because their nutritional and environmental requirements are usually very specific,” he adds.
Valuables from sugar
The bacterium Caulobacter crescentus is one of these special fellows, which can, for example, utilise the sugar xylose. Xylose is an essential component of plant cell walls and accounts for up to 20 per cent of plants’ biomass, including sugar cane. The bacterial decomposition of xylose generates intermediates that are of great interest to industry:
D-xylonate could be used in the production of cement and food dyes in the future; succinate is already being used in the production of plastics and solvents; and α-ketoglutarate is a sought-after raw material for food supplements and medicines. The abilities of Caulobacter crescentus are therefore in demand. However, the bacterium has the property of attaching itself almost inseparably to surfaces in humid environments. “As a result, this bacterium is a nightmare for process development”, says Stephan Noack. “It would simply colonise and clog all the walls, pipes and the sensor technology of our laboratory facilities.”
Microbiologist Jan Marienhagen and engineer Stephan Noack work closely together when it comes to making bacteria fit for industrial use. The robust and undemanding soil bacterium Corynebacterium glutamicum, in contrast, is a good-natured laboratory workhorse. It has enjoyed great popularity in research and industry for more than 60 years. With its help, biotechnology companies manufacture products worth several billion euros per year, such as vital amino acids for infusion solutions or as additives for animal feed.
Surprises included
Gene transfer between the two types of bacteria could thus be the solution. For this purpose, the researchers first looked closely at how Caulobacter crescentus manages to crack the hard-to-digest sugar xylose. They studied both the enzymes involved and the associated genes that encode them, as well as the sequence of the five reaction steps in the conversion of xylose into energy and other metabolic products.
Surprisingly, Corynebacterium glutamicum already has three of these five steps by nature, as the research group around Jan Marienhagen found. In addition, the bacterium, which is actually very well researched, surprised the scientists with a bonus: a previously unknown enzyme that accelerates the fifth and final step in this process. “The required modifications of the natural metabolism to transfer the abilities of Caulobacter to Corynebacterium for xylose utilization could therefore be reduced,” says Marienhagen in describing the procedure. “The fewer interventions, the less stress for the cells. Ultimately, they need to feel comfortable in the bioreactor. This is the only way to achieve good yields of the desired substances later,” adds Stephan Noack.
1per cent
of world harvests become plant waste.
The team is currently testing whether the productivity of Corynebacterium glutamicum can be further increased in the laboratory. To achieve this, the researchers do not rely on further gene transfers, but on specific changes in laboratory conditions. For example, they examine whether their workhorse adapts when the nutrient supply varies. “The current yield of the sought-after substances from the new strains bred in this way is already very promising on a laboratory scale,” says a delighted Stephan Noack. The industry is also interested and has requested initial samples of the bacterially produced D-xylonate to test its suitability for cement production.
Sugar as a raw material could also come from another source, namely the regional food industry: using bacteria, the UpRePP project of the BioökonomieREVIER Rheinland aims to convert sugar-containing waste into polymer components, for example to produce bioplastics. Jan Marienhagen, Stephan Noack and Nick Wierckx are collaborating with RWTH Aachen University in the project. First results are expected in 2021.
Read more about biotechnology and the bioeconomy at Jülich in the blog (in German): blogs.fz-juelich.de/biooekonomie
Brigitte Stahl-Busse
Artistic waste recycling
Czech artist Veronika Richterova, too, uses plastic waste as a raw material: she has been creating lamps, sculptures, animals and plants out of PET bottles, including the flowers on our cover, since 2004. By now, the artist has turned thousands of bottles into objets d’art. More of her work can be seen at:
www.veronikarichterova.com/en
Biotechnology unites
Jülich researchers are looking deep into the cells: they want to understand how they work, where their particular strengths, and weaknesses, lie. To do so, they are deciphering the chemical, biological and genetic make-up of microorganisms and exploring their metabolism in order to realign it for various applications. “Thanks to such optimised microorganisms, superior products can be produced from plant and industrial residues and raw materials. This makes it clear: biotechnology is a crucial element in establishing a true recycling economy in the sense of a sustainable bioeconomy,” explains Prof. Wolfgang Wiechert, Director of Jülich’s Biotechnology institute (IBG-1). To this end, the researchers have been working closely with scientists from a wide range of disciplines for over ten years, both internationally and within the Bioeconomy Science Center, a network of RWTH Aachen University, Forschungszentrum Jülich and the universities of Düsseldorf and Bonn. They are also involved in the structural change of the model region BioökonomieREVIER Rheinland. “We are researching questions here for which there are no standard solutions yet,” emphasises Wiechert.
Images: Forschungszentrum Jülich/Sascha Kreklau, Elena Elisseeva/Shutterstock.com, Veronika Richterová, Roses (2007), Photo: Michal Cihlář