Heterologous expression of Aspergillus terreus fructosyltransferase in Kluyveromyces lactis

• First paper on the functional heterologous secretory expression of fructosyltransferase (FTase) from A. terreus NIH2624.
• Yield of recombinant FTase was high, and reached 986.4 U/mL in a 5-L fermentation.
• The recombinant enzyme produced significant levels of GF5 as well as GF6.

Fructo-oligosaccharides are prebiotic and hypocaloric sweeteners that are usually extracted from chicory. They can also be produced from sucrose using fructosyltransferases, but the only commercial enzyme suitable for this purpose is Pectinex Ultra, which is produced with Aspergillus aculeatus. Here we used the yeast Kluyveromyces lactis to express a secreted recombinant fructosyltransferase from the inulin-producing fungus Aspergillus terreus. A synthetic codon-optimised version of the putative β-fructofuranosidase ATEG 04996 (XP 001214174.1) from A. terreus NIH2624 was secreted as a functional protein into the extracellular medium. At 60°C, the purified A. terreus enzyme generated the same pattern of oligosaccharides as Pectinex Ultra, but at lower temperatures it also produced oligomers with up to seven units. We achieved activities of up to 986.4 U/mL in high-level expression experiments, which is better than previous reports of optimised Aspergillus spp. fermentations.

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