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Production of Organic Acids in Fungal Hosts

Authors: 
Penttilä, M., VTT Technical Research Centre of Finland

Biotechnological production of organic acids has gained significant interest in providing bio-based platform chemicals for various applications. Fungi, both yeast and filamentous fungi, offer a possibility for low pH biotechnological production, advantageous for downstream processing. Many filamentous fungi produce hydrolytic enzymes, allowing polymeric carbohydrates to be used as raw material in bioprocesses.

We have engineered various yeast and filamentous fungi for production of organic acids. Synthetic biology tools are essential for high through put strain development. For this purpose methods like CrispR, and synthetic promoters have been set up in various fungal hosts, in particular targeting for fungal production hosts with high industrial potential.

Nature biodiversity has enormous potential for creating novel industrial hosts. We have generated a pipeline to identify novel industrial fungal production hosts, including strain selection (tolerance to low pH, acids, hydrolysates etc.), construction of metabolic engineering tool boxes, and physiology studies - up to industrial implementation.  

For metabolic engineering of a model pathway for production of xylonic acid, a number of steps were taken: enzyme candidates were identified by bioinformatic data mining, their properties characterized and structure determinations and site-directed mutagenesis were carried out. NMR methods were used to monitor the kinetics of selected pathway enzymes and in vivo reactions. Our studies also highlighted global transcriptomic responses and intracellular accumulation of acid.

Choice of host, gene, pathway and production process (typically batch or fed batch) have all been found to be important in achieving high levels of organic acid production.