Bioconversion of D-galacturonate to keto-deoxy-L-galactonate

• Published in: BMC biotechnology 2010-08, Vol.10, p.63
• Main Authors: Wiebe, Marilyn G, Mojzita, Dominik, Hilditch, Satu, Ruohonen, Laura, Penttilä, Merja
• Format: Article
• Language: English
• Subjects: Molds (Fungi); Phytochemicals; Production processes; Properties
• ISSN: 1472-6750; 1472-6750
• DOI: 10.1186/1472-6750-10-63

The D-galacturonic acid derived from plant pectin can be converted into a variety of other chemicals which have potential use as chelators, clarifiers, preservatives and plastic precursors. Among these is the deoxy-keto acid derived from L-galactonic acid, keto-deoxy-L-galactonic acid or 3-deoxy-L-threo-hex-2-ulosonic acid. The keto-deoxy sugars have been found to be useful precursors for producing further derivatives. Keto-deoxy-L-galactonate is a natural intermediate in the fungal D-galacturonate metabolic pathway, and thus keto-deoxy-L-galactonate can be produced in a simple biological conversion. Keto-deoxy-L-galactonate (3-deoxy-L-threo-hex-2-ulosonate) accumulated in the culture supernatant when Trichoderma reesei [DELTA]lga1 and Aspergillus niger [DELTA]gaaC were grown in the presence of D-galacturonate. Keto-deoxy-L-galactonate accumulated even if no metabolisable carbon source was present in the culture supernatant, but was enhanced when D-xylose was provided as a carbon and energy source. Up to 10.5 g keto-deoxy-L-galactonate l.sup.-1 .sup.was produced from 20 g D-galacturonate l.sup.-1 .sup.and A. niger [DELTA]gaaC produced 15.0 g keto-deoxy-L-galactonate l.sup.-1 .sup.from 20 g polygalacturonate l.sup.-1.sup., at yields of 0.4 to 1.0 g keto-deoxy-L-galactonate [g D-galacturonate consumed].sup.-1.sup.. Keto-deoxy-L-galactonate accumulated to concentrations of 12 to 16 g l.sup.-1 .sup.intracellularly in both producing organisms. This intracellular concentration was sustained throughout production in A. niger [DELTA]gaaC, but decreased in T. reesei. Bioconversion of D-galacturonate to keto-deoxy-L-galactonate was achieved with both A. niger [DELTA]gaaC and T. reesei [DELTA]lga1, although production (titre, volumetric and specific rates) was better with A. niger than T. reesei. A. niger was also able to produce keto-deoxy-L-galactonate directly from pectin or polygalacturonate demonstrating the feasibility of simultaneous hydrolysis and bioconversion. Although keto-deoxy-L-galactonate accumulated intracellularly, concentrations above ~12 g l.sup.-1 .sup.were exported to the culture supernatant. Lysis may have contributed to the release of keto-deoxy-L-galactonate from T. reesei mycelia.