Industrial biotechnology is a key research area of the Stuttgart-based Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB, which is managed by Prof. Dr. Thomas Hirth. The IGB's scientists and engineers investigate how renewable resources can be used as biogenic raw materials. The "White Biotechnology" research group in the Department of Molecular Biology, led by Dr. Steffen Rupp (head of department), works on the entire processing chain, from biobased basic material to a product that can be used in the chemical or polymer industries.

Susanne Zibek, technical biologist, engineer and head of the "White Biotechnology" research group, divides the process into different working steps: "We investigate and develop the upstream process by preparing the renewable materials so that they can be used by microorganisms," explains Zibek. Biotransformation is another working step, where the Fraunhofer IGB develops methods to enable the conversion of a raw material into a product. "We try to understand the metabolic pathways in order to be able to optimise the conversion processes during the fermentation of substrates and obtain higher product yields," said Zibek. Potential products are long-chain dicarboxylic acids.

In addition to the optimisation of bacterial strains, enzyme screening is another tool used to identify new biocatalysts for use in the field of industrial biotechnology. The aim of screening is to find new enzymes or microorganisms and make them suitable for industrial application. The IGB researchers used this method to search for chitinases, which enable the efficient conversion of chitin into its monomeric constituents (N-acetylglucosamine). "We examined a soil sample which was believed to contain chitin and hence also microorganisms that are able to degrade it," said Zibek highlighting that both the exoskeleton of forest insects and the cell walls of fungi contain chitin. The researchers use enrichment cultures to grow the microorganisms in the soil sample and subsequently determine the activity of the chitinases using special assays.

Since however the majority of natural microorganisms cannot be cultivated in the laboratory, the researchers chose to use another method to determine chitinase activity: They established a metagenome library. "The advantage of such libraries is that the entire DNA of the soil sample can be introduced into bacteria such as Escherichia coli, that can be easily cultivated and analysed," said Susanne Zibek. In the case of chitin, the researchers were able to identify several enzymes that are able to degrade chitin in the enrichment cultures.

The Fraunhofer researchers use long-chain dicarboxylic acids for the production of plastics as an alternative to fossil raw material sources. "The chemical production of long-chain dicarboxylic acids is quite difficult as it generates many side products," said Susanne Zibek. The Fraunhofer IGB has therefore developed a biotechnological method for the production of long-chain dicarboxylic acids. The yeast Candida tropicalis is able to produce long-chain dicarboxylic acids through omega oxidation, a process through which oleic acid in rapeseed oil is converted into 1,18 octadecenoic acid. "First, a specific lipase cleaves the triglycerides of rapeseed oil into oleic acid and glycerol," explains Zibek. The yeast is subsequently able to produce alpha, omega dicarboxylic acid. "We mainly focused on making the process more economic," said Zibek. Mineral salt media enable the product to be purified more easily. In addition, methods such as high-cell density fermentation lead to high biomass concentrations, which in turn lead to a high conversion rate and hence high quantities of the desired product. "The optimisation of processes is aimed at achieving a high product formation rate," said Zibek. At present, the Fraunhofer IGB is developing new strains that can produce dicarboxylic acids in order to have at their disposal an alternative to the pathogenic Candida yeast strain.