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A fungus converts cellulose directly into a platform chemical

| By Gerald Ondrey

Conventional bioprocesses use three separate steps to convert cellulose into products, such as bioplastics and biofuels. The consolidated bioprocess (CBP) combines all steps — cellulase production, cellulose hydrolysis and product fermentation — in a single reactor.

Using the natural abilities of the non-genetically modified fungus, Talaromyces verruculosus, a research team from the Leibniz Institute for Natural Product Research and Infection Biology — Hans Knöll Institute (Leibniz-HKI; Jena, Germany; has discovered a method for the efficient conversion of cellulose into enantiopure erythro-isocitric acid — a chiral isomer of citric acid with a large potential as a chemical building block. The study was published by the Jena team in the journal ACS Sustainable Chemistry & Engineering.

As natural metabolic products of most living organisms, citric acid and isocitric acid are among the most widespread acids in nature. Citric acid is produced industrially in large quantities using the mold fungus Aspergillus niger. With a global production of around 2.8 million ton/yr, it is one of the highest-volume biotechnological products. However, citric acid is produced from sugar and is therefore in direct competition with food production, so its use as a building block has so far been neither economical nor sustainable.

Isocitric acid is very similar to citric acid (diagram); only one hydroxyl group is positioned on a different carbon atom. This makes the molecule asymmetric, with two different diastereomers: threo– and erythro-isocitric acid. Each diastereomer has two mirror-image variants, the D- and L-forms. Citric acid and isocitric acid have almost identical properties and it can be assumed that the iso form would be just as widely applicable. The reason why this is not the case is that there has not yet been an efficient production process for pure isocitric acid, so it is currently only available as an expensive (€18,000/kg) research chemical. However, the new — now patented — production process enables sustainable and inexpensive production from plant waste and residues, such as straw, waste paper or wood residues, which could make it possible to produce isocitric acid even more cheaply than citric acid in the future.


Source: Friederike Gawlik/Leibniz-HKI